Module 2: Biological Classification of Microorganisms PDF

Republic of the Philippines BICOL UNVERSITY TABACO M.H. del Pilar St., Tayhi, Tabaco City 4511, Albay Email: [email protected] MODULE 2: THE BIOLOGICAL CLASSIFICAT...

Republic of the Philippines BICOL UNVERSITY TABACO M.H. del Pilar St., Tayhi, Tabaco City 4511, Albay Email: [email protected] MODULE 2: THE BIOLOGICAL CLASSIFICATION OF THE MICROORGANISMS Course Code & Title: Micro 11 / General Microbiology Course Placement: Bachelor of Science in Food Technology I Delivery / Duration: Weeks 4-5 / 13.5 hours Name of Professor: Dr. Alex P. Camaya Position/Specialization: Assoc. Professor IV/ Cell Structure and Function  MODULE 2: THE BIOLOGICAL CLASSIFICATION OF THE MICROORGANISMS WHAT IS THIS MODULE ABOUT? This module primarily mainly aims to discuss the general characteristics of the microorganisms consisting of the prokaryotic organisms such as the bacteria, the eukaryotic organisms such as the fungi, algae and protozoans, and the acellular organisms such as the viruses. Along this aspect, the biological classification deals with the morphology, cellular composition, reproduction, distribution and importance of these five important groups of microorganisms, which mainly separate them from one another. WHAT WILL YOU LEARN HERE? This module contains five (5) lessons, namely as follows; Lesson 1: The Bacteria Lesson 2: The Fungi Lesson 3: The Viruses Lesson 4: The Algae Lesson 5: The Protozoa LET’S READ AND STUDY! Lesson 1: The Bacteria Bacteria are characterized based on the cell shape, size and structure cell arrangement, occurrence of special structures and developmental forms, staining reactions and motility and flagella arrangement. They are also characterized by the cell wall component, Gram stain reaction, cellular respiration and mode of nutrition. This unit examines the general characteristics of bacteria, shapes and forms of bacteria, structures external and internal in bacteria among other things. Distinguishing Characteristics of Bacteria bacteria are prokaryotic organisms; they are simplest of all microbial cells; they are single celled organisms; they have distinctive cell wall which contain peptidoglycan they are measured in unit called micrometer  bacteria lack a true nucleus but have a region called the nucleroid region where DNA is free floating; they may have additional DNA called a plasmid; their reproduction is by binary fission; they are extremely diverse and numerous in soils and waters. Size, Shape and Arrangement of Bacterial Cell Size - Bacteria are very small, 0.5 to 1.0μm in diameter. Because of their small size, they have high surface area/volume ratio which results in a high growth and metabolism rate. No circulatory mechanism is needed for nutrients taken in because the mass of cell substance to be nourished is very close to the surface. Examinations of a microbial cell require the use of a high power microscope usually of about 1,000 diameters. Shape and Arrangement - The shape of a bacterium is governed by its rigid cell wall which gives it a definite shape. The typical shapes of bacteria are: a. Cocci (singular: Coccus), e.g. Staphylococcus b. Bacilli (singular: Bacillus), e.g. Bacillus subtilis c. Vibrios (singular: Vibrio) d. Spirilla (singular: Sprillum) e. Spirochetes (singular: Spirochete), e.g. Treponema pallidum Some species of bacteria are pleomorphic, i.e. they are able to change their forms especially when grown on artificial media. a. Cocci are round, oval or spherical in shape. Its diameter characteristic arrangement when multiplying is based on arrangement of cells as: i. Diplococci (cocci in pairs e.g. Meningococci and Gonococci) ii. Streptococci (cocci in chains) iii. Staphylococci (cocci in irregular clusters like a bunch of grapes). iv. Tetracocci (cocci in a group of four cells) v. Sarcinae (cocci in regular clusters) b. Bacilli are rod-shaped, stick-like bacteria with rounded, square, tapered or swollen ends. They measure 1-10 μm in length by 0.3-1.0 μm in width. Bacilli are not arranged in patterns as complex as cocci. Most occur singly. Other arrangements are: i. Diplobacilli (rods in pairs) ii. Streptobacilli (rods in chains) iii. Trichomes (similar to chains but have larger area of contact between adjacent cells) iv. mass together e.g. Mycobacterium leprae.  v. palisade arrangement cells are lined side by side like matchsticks and at angles to each other like Chinese lecters, e.g. Corynebacterium diptheriae. c. Vibrios are small slightly curved rods,or comma shaped 3-4μm in length by 0.5μm in width. Most are motile with a single flagellum at one end, e.g. Vibrio cholerae. d. Spirilla are helical bacteria, small, regularly coiled, rigid, organisms measuring 3-4μm in length. Each coil measures about 1μm, e.g. Spirillum minus. e. Spirochetes are helical, (complete twist), flexible, coiled organisms, can twist and contort their shapes. Spirochetes are divided into three main groups; i. Treponemes - Tiny and delicate with regular tight coils, measuring 6-15μm by 0.2μm in width, e.g. T. pallidum and T. pertenue. ii. Borreliae - Large spirochaetes with irregular open coils 10-20μm in length by 0.5μm in width, e.g. Borrelia duttoni and Borrelia vinceti. iii. Leptospires - Tiny spirochetes with many tightly packed coils that are difficult to distinguish; 6-20μm in length by 0.1μM in width and have hooked ends, e.g. Leptospira interrigans. In addition to the common bacterial shapes, many others also occur in different shapes, which include: i. pear shaped cells, e.g. Pasteuri ii. lobed spheres, e.g. Sulfolobus iii. rods with squared ends, e.g. Bacillus anthracis iv. disk arranged stacks of coins, e.g. Caryophanon v. rods with helically sculptured surfaces, e.g. Seliberia and others The shape of a cell affects its survival and activity in the environment. Figure 1. Different morphological types of the bacteria. Figure 2. Structures and functions of a typical bacteria Bacterial Structures Examination of a bacterial cell will reveal several components and structures. Some are external to the cell wall while others are internal to the cell wall. Structure External to the Cell Wall 1. Flagella (singular: Flagellum) - These are hair like, helical appendages that protrude through the cell wall, 0.01 – 0.02 μm in diameter and simple in structure. Based on their location on the cell, flagella may be polar (at one or both ends of bacterium) or lateral (along the sides of the bacterium). Bacteria propel themselves by rotating their helical flagella. A flagellum is composed of three parts: a. based body associated with the cytoplasmic, membrane and cell wall. b. a short hook and a helical filament which is usually several times as long as the cell. c. a flagellum grows at the tip rather than at the base. The types of flagella are; a. monotrichous - a single polar flagellum. Many that appears and functions as monopolar or bipolar flagella consist of bundles of 2 to 50 single units (polytrichous). b. lophotrichous - a cluster of polar flagella. c. amphitrichous - flagella, either single or clusters at both cell poles. d. peritrichous - cell surrounded by lateral flagella. Figure 3. Diagrammatic illustration of the types of bacterial flagella (left) and its structure (right) 2. Pili (sing: pilus) - They are also called fimbriae. They are hollow, non- helical filamentous appendages that are thinner, shorter and more numerous than flagella: long, thin, straight threads 3-25μm in diameter and 12 μm in length. They do not function in motility since they are found on non-motile and motile species. Several functions are associated with different types of pili. The F pilus (sex pilus) serves as the path of entry of genetic material during bacterial mating. Some play major role in human infection by allowing pathogenic bacteria to attach to the epithehal cells lining the respiratory, intestinal or genitourinary tracts, this prevents the bacteria from being washed away by the flow of mucous or body fluids and permits infections to be established. 3. Capsules - This is a viscous substance forming a covering layer or envelope around the cell wall of some bacteria. Capsules can be categorized into three based on their visualization by light microscope using special staining methods. If the covering layer can be visualized by light microscope using special staining methods, it is termed capsule. a. Microcapsule - If the layer is too thin to be seen by light microscope. b. Slime - If it is so abundant that many cells are embedded in a common matrix. Most bacterial capsules consist of polysaccharides which can be homopolysaccharides or heteropolysaccharides. Homopolysaccharides - Capsule made up of/composed of a single kind of sugar usually synthesized outside the cell by exocellular enzymes, e.g. glucan (a polymer of glucose) from sucrose by S. mutans. Heteropolysaccharides - Composed of several kinds of sugars. A few capsules are polypeptide, e.g. Bacillus anthracis has a capsule made up of a polymer of glutamic acid. The functions of the capsules are: a. They may provide protection against temporary drying by binding water molecules. b. They may block attachment of bacteriophages. c. They may be antiphagocytic, i.e. they may inhibit the engulfment of pathogenic bacteria by white blood cells. Hence contribute to invasive or infective ability (virulence). d. Promote attachment of bacteria to surfaces. 4. Sheaths - Some bacterial species form chains or trichomes enclosed by a hollow tube called sheaths. These sheaths consist of a heteropolysaccharides containing glucose, glucuronic acid, galactose  and fucose. Its functions in a few bacteria, are to facilitate moderate change of position. Likewise, sheaths enable individual cells to stay associated in cell colonies. 5. Prosthecae and Stalks Prosthecae - They are semi rigid extensions of the cell wall and cytoplasmic membrane and have a diameter less than that of the cell. Found in some aerobic bacteria from fresh water and marine environment. Its function is to increase surface area of the cell for nutrient absorption. Some have adhesive substances that aid attachment to surfaces. Stalks - They are non-living ribbon -like or tubular appendages excreted by some bacterial cells, e.g. found in Gallionella or Planctomyces. Its functions is to aid in attachment. 6. Cell Wall - It is a very rigid structure that gives shape to the cells. It also prevents the cell from expanding and eventually bursting of uptake of water since most bacteria live in hypotonic environment (i.e. environments having a lower osmotic pressure than exists within the bacterial cells). Cell walls are essential for bacterial growth and division. Structure and chemical composition of the cell wall - The cell wall of bacteria is made up of peptidoglycan (sometimes called murein). Peptidoglycan is found only in prokaryotes. It is an insoluble, porous, cross-linked polymer. Peptidoglycan differs in composition and structure from one species to another but it is basically a polymer of N- acetyglucosamine, N-acetylmuramie acid, L-alanine, D-alanine, D- glutamate and adiamino acid. Bacteria are classified based on differences in the composition of cell wall. This is determined by the Gram stain technique. Gram stain identifies bacteria as Gram positive or Gram negative. The Gram stain is named after Christian Gram, a Danish physician who invented it in 1884. Gram positive bacteria stained purple whereas Gram negative bacteria stain pink or red by the Gram stain technique. The difference is the reaction to the Gram staining technique is due to the presence of a single 20 to 80μm thick homogenous layer of peptidoglycan (murein) which is present in the all wall of Gram positive bacteria on the other hand, the Gram negative cell is more complex, it has a 2 to 7μm peptidoglycan layer covered by 7 to 8μm thick outer layer of lipopolysaccharides (LPS). These LPS are toxic substances which make Gram negative organisms more harmful than Gram positive organisms.  Structures Internal to the Cell 1. Cytoplasmic Membrane This lies immediately beneath the cell wall. It is approximately 7.5 μm (0.0075 μm) thick and composed primarily of phospholipids (20 to 30 percent) and protein (60 to 70 percent). It serves as a barrier to most water soluble molecules. It contains various enzymes involved in respiration, and metabolism and in synthesis of capsular and cell wall component. Proteins are also synthesized in the cytoplasm. 2. Protoplast - A protoplast is the portion of a bacterial, all made up of the cytoplasmic membrane and the cell material bounded by it. 3. Cytoplasm - This is the cell material bounded by the cytoplasmic membrane and it may be divided into: a. The cytoplasmic area, granular in appearance and rich in the macromolecular RNA-protein bodies called ribosomes on which proteins are synthesized. b. The chromatin area rich in DNA and; c. The fluid portion with dissolved substances. 4. Nuclear Material - Unlike eucaryotic cells bacterial cells do not have a distinct membrane enclosed nucleus but they have an area near the center of the cell that is regarded as the nuclear structure, the DNA of the cell is confined to this area. The DNA is circular and bears the genes of the cell. 5. Spores and Cysts - Certain bacteria produce spores either within the cells (endospores) or external to the cell (exospores). The spore is metabolically dormant form which under appropriate condition can germinate to form a vegetative cell. Endospores are extremely resistant to desiccation, staining, disinfecting chemicals, radiation and heat. Cysts are also dormant, thick walled desiccation resistant forms that can germinate also under favorable conditioning. Nutrition The nutrition requirements of bacteria vary widely. Based on their source of energy, they are classified as: a. Phototrophs - These are bacteria that use light energy as their energy sources. b. Chemotrophs - They obtain their energy by oxidizing inorganic or organic – chemical compounds. Based on the source of carbon which is the major source of nutrient for all cells bacteria can be classified as:  a. Heterotrophs - These are bacteria that derive carbon from preformed organic nutrients such as sugar or carbohydrate. b. Autotrophs - They derive carbon from inorganic sources such as carbon dioxide. Cellular Respiration Based on whether they need oxygen to survive or not, bacteria may be: a. Aerobic or strict aerobes - these require oxygen, e.g. Bacillus cereus. b. Anaerobic bacteria or strict anaerobes - they cannot tolerate oxygen, e.g. Clostridium spp. c. Facultative anaerobes - These are generally aerobes but have the capacity to grow in the absence of oxygen, e.g. Staphylococcus spp. Figure 4. Bacterial differences and classification. Gram positive (+) and Gram negative (-) bacteria have differences in cell wall and outer envelope. The theory of why the gram stains works is based on this difference. Reproduction Bacteria reproduce mainly by asexual method which most of the time is transverse binary fission (see illustration below). This is a process in which a bacterial cell divides to give two daughter cells after developing a transverse septum (cross wall). Figure 5. Schematic diagram of bacterial division by binary fission. Lesson 2: The Fungi Fungi are eukaryotic spore-bearing organisms that lack chlorophyll and generally reproduce both sexually and asexually. They are of great practical and scientific importance. One of the reasons for this is that many fungi are of microscopic cellular dimensions. Fungi have a diversity of morphological appearances depending on the species. Fungi comprise the molds, mushrooms and yeasts. Molds are filamentous and multicellular while yeasts are unicellular. They are widely distributed and found wherever moisture is present. They are of great importance to man in both beneficial and harmful ways. This unit examines the general characteristics of fungi, the distribution, morphology, nutrition and reproduction of fungi. Distinguishing Characteristics of Fungi They are large, diverse and widespread group of organisms, the molds, mushrooms and yeasts. Fungi are eukaryotic organisms. They are members of the domain Eukarya. They contain a membrane-enclosed nucleus and several other organelles. They have no chlorophyll. They are chemo-organotrophic organisms. The body of the fungi is called thallus (similar term used to the body of seaweeds/algae) The thallus may consist of a single cell as found in yeasts. The thallus may consist of filaments, 5 to 10 μm across which are commonly branched as found in molds. The yeast cell or mold filament is surrounded by a true cell wall (exception is the slime mold which have a thallus consisting of a naked amoeboid mass of protoplasm). Some fungi are dimorphic, that is they exist in two forms. Some pathogenic fungi of humans and other animals have a unicellular and yeast like form in their host but when growing saprophytic in soil or on a laboratory medium they have a filamentous mold form. Habitat distribution of fungi is diverse. Some are aquatic, living primarily in fresh water and a few marine fungi are terrestrial. They inhabit soil and dead plant. Some are parasitic, inhabiting and infecting living hosts either plants or animals. Some form beneficial relationships with other organisms as mycorrhizae. The study of fungi is known as mycology. Structure and Forms of Fungi The body or vegetative structure of a fungus is called a thallus (plural thalli). It varies in complexity and size ranging from the single cell microscopic yeasts to multicellular molds and mushrooms. The fungal cell is usually enclosed in a cell wall of chitin.  The Yeasts They are unicellular fungi that have a single nucleus. They are commonly egg-shaped but some are elongated and some spherical. Yeasts have no flagella or other organelles of locomotion. They possess most of the other eukaryotic organelles. Yeast cells are larger than most bacteria. Yeasts vary considerably in size ranging from 1 to 5μm in width and from 5 to 30 μm or more in length. They reproduce asexually by budding and traverse division or sexually through spore formation. The Molds The thallus of a mold consists of long branched threadlike filaments of cells called hyphae. These hyphae form a mycelium which is a tangled mass or tissue like aggregation of hyphae. Hyphae Each hypha is about 5 to 10μm wide. Hyphae are composed of an outer tube-like wall surrounding a cavity the lumen which is filled or lined by protoplasm. Between the protoplasm and the wall is the plasmalemma, a double layer membrane which surrounds the protoplasm. The hyphal wall consists of microfibrils composed of hemicelluloses or chitin. True cellulose occurs only in the walls of lower fungi. Wall matrix material in which the microfibrils are embedded consists of proteins, lipids and other substances. Growth of a hypha is distal near the tip. Mycelium The mycelium is a complex of several filaments called hyphae (sing.: hypha). New hyphae generally arise from a germinated spore. The germinated spore puts out a germ tube or tubes which elongate to form hyphae. These hyphae form a tangled mass or tissue like aggregation. In some fungi, protoplasm streams through hyphae uninterrupted by cross walls, these hyphae are called coenocytic or aseptate. The hyphae of others have cross walls called septa (s. septum) with either single pore or multiple pores that enables cytoplasmic streaming. These hyphae are termed septate.  In summary, hyphae can be said to occur in three forms: Non-septate or coenocytic, such hyphae have no septa. Septate with uninucleate cells. Septate with multinucleate cells. Each cell has more than one nucleus in each compartment. Figure 6. Diagrammatic illustration of yeast and mold structures Nutrition and Metabolism Most fungi are saprobes, securing their nutrients from dead organic matters. They release hydrolytic exo-enzymes that digest external substrates and absorb the soluble products. They are also chemo-organo heterotrophs, i.e. they use organic compounds as a source of carbon, electrons and energy. Fungi are usually aerobic; however, some yeasts are facultatively anaerobic and can obtain their energy by fermentation. Obligate anaerobic fungi are found in the rumen of cattle. Reproduction Asexual Reproduction - Asexual reproduction is a type of reproduction involving only one parent that produces genetically identical offspring by budding or by the division of a single cell or the entire organism into two or more parts. Asexual reproduction, also called somatic or vegetative reproduction is accomplished in several ways and does not involve the fusion/union of nuclei, sex cells or sex organs. It may be accomplished by: Fission of somatic cells yielding two similar daughter cells Budding each bud, a small outgrowth of the parent cell develops into a new individual Fragmentation or disjointing of the hyphal cells each fragment becoming a new organism Spore formation. There are several types of asexual spores each with a name. Sporangiospores - These are single-celled spores formed within sacs called sporangia (sing.: sporangium) at the end of special hyphae called sporangiospores). The two types of sporangiospores are aplanospores which are non-motile and zoospores which are motile. Motility is due to the presence of flagella. Conidiospores or conidia (sing.: conidium). These are formed at the tip or side of a hypha. Single celled conidia are called microconidia while large multi-celled conidia are called macroconidia. Oidia (sing.: oidium) or Arthrosopores - These are single-celled spores formed by disjointing of hyphal cells. Chlamydospores - These are thick walled single celled spores which are highly resistant to adverse conditions. They are found from cells of the vegetative hypha. Blastospores - These are spores formed by budding. Sexual Reproduction - Sexual reproduction is a type of reproduction in which two parents give rise to offspring that have unique combinations of genes inherited from the gametes of the two parents. It is carried out by fusion of the compatible nuclei of two parent cells. The process of sexual reproduction begins with the joining of two cells and fusion of their protoplast (plasmogamy) thus enabling the two haploid nuclei of two mating types to fuse together (karyogamy) to form a diploid nucleus. This is followed by meiosis, which again reduces the number of chromosomes to the haploid number. The sex organelles of fungi if present are called gametangia. They may form differentiated sex cells called gametes or may contain instead one or more gamete nuclei. If the male and female gametangia are morphologically different, the male gametangium is called the antheridium (plural: antheridia) and the female gamentangium is called the oogonium (oogonia).  Methods of sexual reproduction includes; Gametic copulation - This is the fusion of naked gametes, one or both of which are motile. Gamete-gametangial copulation - Two gametangia came into contact but do not fuse; the male nucleus migrated through a pore or fertilization to be into the female gamentangium. Gametangial copulation - Two gamentangia or their protoplast fuse and give rise to a zygote that develops into a resting spore. Somatic copulation - Fusion of somatic or vegetative cells. Spermatization - Union of a special male structure called a spermatium (plural spermatia) with a female receptive structure. The spermatium empties its content into the female during plasmogamy. Sexual spores are produced by the fusion of two nuclei. Examples are; Ascospores - These are single-celled spores produced in a sac called an ascus. There are usually eight ascospores in each ascus. Basidiospore - These are single celled spores borne on a club-shaped structure called a basidium. Zygospores - These are large thick walled spores formed when the tips of two sexually compatible hyphae or gametagia fuse together. Oospores - These are formed with a special female structure, the oogonium. Fertilization of the eggs or oospheres by the male gametes formed in an antheridium give rise to oospores. Physiology Fungi are better able to withstand certain extreme environments than other microorganisms. They can tolerate more acidic conditions than other microbes. Some types of yeasts are facultative; they can grow under both aerobic and anaerobic conditions. Molds and many types of yeast are usually aerobic microorganisms. Fungi grow over a wide range of temperature. The optimum temperature for most saprobic species is 22 to 300°C, while pathogenic fungi have a higher temperature optimum of 30 to 370°C. Some fungi will grow at or near 00C and thus can cause spoilage of meat and/or vegetables in cold storage. Importance About 90,000 fungal species have been described according to literature. However, some estimates suggest that 1.5 million species may exist. Fungi are important to humans in both beneficial and harmful ways. Beneficially, fungi act as decomposers. They degrade complex organic materials in the environment and release simple organic and inorganic molecules like carbon, nitrogen, phosphorus needed by other living organisms.  Molds and yeasts are used in many industrial processes involving fermentation to produce beer, wine and bread, cheese, soy-sauce, organic acids and many antibiotics. They are important research tools in the study of fundamental processes such as cytology, genetics, biochemistry and microbiology. On the other hand, fungi cause many diseases of plants, animals and humans. About 20 new human fungal pathogens are documented each year. Figure 7. Schematic illustration of fungal dimorphism. Lesson 3: The Viruses Viruses are acellular entities. They are genetic elements that cannot replicate independently of a living cell called the host cell. Viruses have extracellular forms which enable them to exist outside the host for long periods. But to multiply, they have to enter a cell in which they can replicate causing infection. Viruses are the most numerous microorganisms on earth and infect all types of cellular organisms. The study of viruses is known as virology. This unit examines the general characteristics of viruses, their structures, genomes, symmetry, replication in hosts and purification. Distinguishing Characteristics of Viruses They are the smallest microorganisms. They range in size from 10 to 400 µm in diameter and can only be viewed under an electron microscope. They are acellular, i.e. not cellular and non-living. They only reproduce when present within living cells. They are infectious agents. A complex virus particle or virion consists of one or more molecules of DNA or RNA enclosed in a coat of protein. Viruses can exist in two phases: extracellular and intracellular. The extracellular phase known as virion possesses few if any enzymes and cannot reproduce independent of living cells. It is metabolically inert and does not carry out respiration. In the intracellular phase, viruses exist primarily as replicating nucleic acids in the host cells that induce host metabolism to synthesize virion components which are later released. Viruses differ from living cells in three ways: They have simple acellular organization. The presence of either DNA or RNA but not both in almost all virions. They do not have the ability to reproduce independent of cells and carry out cell division as procaryotes and eukaryotes do. Size of the Virion Virions range in size from about 10 to 400μm in diameter. The smallest viruses are a little larger than ribosomes whereas the pox viruses which include vaccinia are about the same size as the smallest bacteria and can be seen in the light microscope. Most viruses however, are too small to be visible in the light microscope and must be viewed with scanning and transmission electron microscope. The Structure of Viruses A virus is made up of a central genetic nucleic acid molecule surrounded by a protein coat called a capsid. The combination of both is called the nucleocapsid. The capsid surrounds and protects the viral nucleic acid. The capsid also gives the virus a characteristic shape and help to establish the specificity of the virus for a particular host cells. Capsids are large macromolecular structures that self-assemble from many copies of one or a few types of proteins. The protein used to build the capsids is called protomers. The simplest virus is a naked virus (nucleocapsid) consisting of a geometric capsid assembled around a nucleic acid. On the other hand, we can have a virus made up of a nucleocapsid surrounded by a flexible membrane called an envelope. This type of virus is called an envelope virus. The various morphology types of viruses result from the combination of a particular type of capsid symmetry with the presence or absence of an envelope which is a lipid layer external to the nucleocapsid. Viral Genomes All cells contain double stranded DNA genomes. By contrast, viruses have either DNA or RNA genomes (one group of viruses does use both DNA and RNA as their genetic material but at different stages of the replication cycle). Hence, we have RNA viruses or DNA viruses. Virus genomes can be classified based on whether the nucleic acid in the virion is DNA or RNA and further subdivided to whether the nucleic acid is single or double stranded. Linear or circular, some viral genomes are circular but most are linear. We can have single stranded DNA, double stranded DNA, single stranded RNA and double stranded RNA. All four types are found in animal viruses. Most plant viruses have single stranded RNA genomes and most bacteria viruses contain double stranded RNA. Capsids Symmetry There are three types of capsid symmetry: helical, icosahedral and complex. 1. Helical Capsids - They are shaped like hollow tubes with protein walls. The tobacco mosaic virus is an example of this virus. In this virus, the self-assembly of protomer in a helical or spiral arrangement produces a long rigid tube, 15 to 18 nm in diameter by 300 nm long. The capsid encloses an RNA genome, which is wound in a spiral and lies within a groove formed by the protein molecule. The size of a helical capsid is influenced by both its protomers and nucleic acid enclosed within the capsid. 2. Icosahedral Capsid - The icosahedral is a regular polyhedron with 20 equilateral triangular faces and 12 vertices and is roughly spherical in shape. It  is one of the nature’s favorite shapes. A few genes sometimes only one can code for protein that self-assemble to form the capsid. These capsids are constructed from ringo-krob-shaped into caller capsomers each usually made up of five or six protomers. Pentamers (pentons) have five subunits hexamers (hexons) have six. 3. Viruses with Capsids of Complex Symmetry (Complex Viruses) - Some virions are more complex than the helical and icosahedral capsid being composed of several parts, each with separate shapes and symmetries. The most complex viruses in terms of structures are some of the bacterial viruses which possess icosahedral heads plus helical tails. In some bacterial viruses such as bacteriophage T4 of Escherichia coli the tail itself has a complex structure. The complete T4 tail has 20 different proteins and the T4 head has several more protein. Figure 8. Schematic diagram of viral capsid symmetry Virus Reproduction Viruses need a host cell in which to reproduce; hence the first step in the life cycle of a virus is attached to a host. This is followed by entry of either the nucleocapsid or the viral nucleic acid into the host. If the nucleocapsid enters uncoating of the genome usually occurs before further steps can occur. Once free in the cytoplasm, genes encoded by the viral genome are expressed, i.e. the viral genes are transcribed and translated. This allows the virus to control the host cell’s biosynthetic machinery so that new virions can be made. The viral genome is then replicated and viral proteins are synthesized. New virions are constructed by self-assembly of coat proteins with the nucleic acids and finally, the matured virions are released from the host. Finally, the steps involved in viral replication or reproduction are:  Attachment of the virion to a susceptible host; Penetration or entry of the virion or its nucleic acid into the host; Synthesis of virus nucleic acid and protein by cell metabolism as directed by the virus; Assembly of capsids and packaging of viral genomes into new virions Release of mature virions from the cell. However, there is great variation in the details of virus reproduction for individual virus species. Figure 9. Schematic illustration of the viral life cycle. The Cultivation of Viruses Because viruses are unable to reproduce independent of living cells, they cannot be cultured in the same way as prokaryotic and eukaryotic microorganisms. Animal viruses are cultivated by inoculating suitable host animals or embryonic egg – fertilized chicken eggs incubated about 6 to 8 days after laying. More recently, animal viruses have been grown in tissue (cell) culture on monolayers of animal cells. Bacterial and Archea viruses are cultivated in either broth or agar cultures of young, actively growing cells. Plant viruses are cultivated in a variety of ways which include plant tissue cultures, cultures of separated cells, or cultures of protoplasts (cells lacking cell wall) and growing of the viruses in whole plants. Virus Purification and Assay Viral purification and Assays are necessary so as to accurately study virus structure, reproduction and other aspects of their biology. Virus Purification - This involves getting or isolating the viral particle in its pure state, purification makes use of several virus properties. The four of the most widely used methods to isolate and purify viruses are: differential and density gradient centrifugation. This is often used in the initial purification steps to separate virus particles from host cells. precipitation of viruses’ particles. denaturation of contaminants. enzymatic digestion of host cells constituents. Virus Assays - The quantity of viruses in a sample can be determined either directly by counting particle numbers using the electron microscope or indirectly by measurement of an observable effect of the virus using techniques such as the hemaglutination assay. Lesson 4: The Algae Algae (sing.: alga) are unicellular microorganisms that have chlorophyll and are photosynthetic. Algae are heterogeneous and range from microscopic unicellular forms to macroscopic seaweeds. They are different from green plants due to their simple reproductive structure for sexual reproduction. Many live in aquatic environments but many also thrive as subterranean algae. Algae are of great importance to biologist because single algal cells are complete organisms capable of photosynthesis and the synthesis of other compounds which constitute the cell. The study of algae is known as phycology. This unit examines the general characteristics, the distribution, the morphology and importance of algae. General Characteristics of Algae Algae are eukaryotic microorganisms. They are photosynthetic microorganisms. Chlorophyll and other pigments are found in membrane-bound organelles known as chloroplasts. Algae contain a discrete nucleus. Other inclusions are starch grains, oil droplets and vacuoles. They contain chlorophyll and utilize light energy to generate their chemical energy. They have a wide range of sizes and shapes. Many species occur as single cells that may be spherical, rod shaped, club-shaped or spindle-shaped. Others are multicellular and appear in every conceivable form, shape and degree of complexity. In most species the cell wall is thin and rigid cell walls of diatoms are impregnated with silica making them thick and very rigid. The motile algae such as euglena have flexible cell membrane called periplasts. They are also able to produce oxygen from water. Occurrence and Distribution Algae are found in many places on earth. They occur in great abundance in the ocean, seas, salt lakes, fresh water lakes, ponds and streams. Many are found in damp soil, on rocks, stones and tree barks. Some are found on plants and animals. Small aquatic forms make up a large part of the free-floating microscopic life in water called plankton which is the principal food for aquatic animals including such large ones as whales. Plankton is generally considered to be composed of both algae and microscopic animal forms. Phytoplankton is made up of plants, i.e. algal forms, and zooplankton is composed of animal organisms. Algae are found where there is sufficient light, moisture and simple nutrients to sustain them. Some species of algae grow on the snow and ice of Polar Regions and mountain peaks, sometimes occurring in such abundance that the landscape becomes colored by the red pigments in their cells. At the other extreme, some algae grow in the hot springs at temperatures as high as 550°C. Some freshwater algae have adapted their metabolism to the high salt concentration found in the brine lakes of the arid South-Western United States. Some algae are adapted to moist soil, the bark of trees and the surface of rocks, which the algae degrade. The decomposition products are made available for soil building and enrichment. Algae are often a problem in water supplies because they produce undesirable taste and odor. Heavy algal growth may form blankets or mats which interfere with the use of some natural waters for recreational purposes. These algal mats may act as barriers to the penetration of oxygen into the water; they prevent photosynthesis by excluding light from deeper water and this may cause fish and other marine animal to suffocate. On the other hand, when dispersed in natural waters, algae increase the oxygen concentration through photosynthesis. Heavy growth of some algae reduces hardness of water and removes slats which are the cause of brackishness. Some algae are endophytic, that is, they are not free-living but live in other organisms. Such algae are widespread in protozoa, mollusks, sponges and corals. Morphology Algae have a wide range of sizes and shapes. Many are unicellular and may be spherical, rod shaped, club shaped or spindle shaped. Others are multicellular and appear in every conceivable forms, shape and degree of complexity including membranous colonies, filaments grouped, singly or in clusters with individual strands which may be branched or unbranched tubes. Algal cells are eukaryotic. Most are thin and rigid cell walls; however, the cell walls of diatoms are impregnated with silica threads which makes them thick and very rigid. Algae have a discrete nucleus, starch grains on droplets and vacuoles: chlorophyll and other pigments are found in membrane-bound organelles known as chloroplasts. The chloroplast ultrastructure and type of pigment presents in algae are used for their classification, e.g. green algae, red algae, yellow-green algae, the golden algae, etc. A very common green microalga is spirogyra; a filamentous alga found on the scum that cover ponds are slow moving water. Motility The motile algae also called the swimming algae have flagella occurring singly or in clusters at the anterior or posterior ends of the cells. Some algae have no means of locomotion and are carried by tides, waves and currents. Some attach themselves to the substrate in the body of water where they live and are occasionally broken loose by currents which move them to new locations. In some forms, only the zoospores, the asexual reproductive cells are motile. Reproduction Algae may reproduce either asexually or sexually. Some species are limited to one of these processes. However, they have complicated life cycles involving both asexual and sexual means of reproduction. Asexual Reproduction in algae include: purely vegetative binary fission; production of unicellular spores, many of which, especially in the aquatic forms have flagella and are motile, these are called zoospores. In terrestrial types of algae, non-motile spores or aplanospores are formed; however, some aplanospores can develop into zoospores. Sexual Reproduction - All forms of sexual reproduction are found among the algae. In this processes there is a fusion (conjugation) of sex cells called gametes to form a zygote. If the gametes are identical, i.e., there is no visible sex differentiation. The fusion process is called isogamous. However, if two gametes are different, the process is called heterogamous. In higher algae, the sex cells are differentiated into male and female. The female egg cell (ovum) is large and non-motile, while the male gametes (sperm cell) is small and are actively motile. This type of sexual reproduction is called oogamy. Biological and Economic Importance Algae as Primary Producers - Algae form the base or beginning of most aquatic food chains because of their photosynthetic activities and are therefore called primary producers of organic matter. Commercial Product from Algae - Many product of economic value is derived from algal cell walls. Three of these, agar, alginic acid and carrageenan, are extracted from the walls of algae. Another, diatomaceous earth, is composed of millions upon millions of diatom glass walls deposited over time on either fresh water or the ocean. All three compounds are used either make gels or to make solution viscous. Carrageenan has been used as a stabilizer or emulsifier in foods such as ice cream and other milk products. It is also used as a binder in toothpaste or in pharmaceutical products, as well as an agent in ulcer therapy. Carrageenan is also useful as a finishing compound in the textile and paper industries, as a thickening agent in sharing creams and lotions and in the soap industry.  Agar is well known as solidifying agent in the preparation of microbiological media. It is obtained from red algae. Species of Gelidium and Gracillaria are used extensively. It is also important in the food industry when it is valuable in the manufacture of processed cheese, mayonnaise, pudding, jellies, baking products and canned goods. In the pharmaceutical industry, agar can be used as a carrier for a drug. Lotions and ointments can contain some agar. About 50% of the ice cream in the U.S. contains alginates which provide a smooth consistency and eliminate ice crystal formation. Alginate is also incorporated into cheeses and bakery products, especially frostings. Other industrial application includes paper manufacturing, the printing of fabrics and paint thickening. Diatomaceous earth is used primarily for filters or filter aids. It is especially suitable because it is not chemically reactive, is not readily compacted or compressed during use and is available in many grades. Algae as Food - Many species of algae (mostly red and brown algae) are used as food in the Far East. Of the red algae are of the most important in Porphyria. It is used as a food in Japan where it is called “nori” and is usually processed into dried sheets. In the Philippines and other South East Asian countries were also known of consuming raw algae (seaweeds) e.g. Caulerpa and Eucheuma as human food. Lesson 5: The Protozoans Protozoa are unicellular, non-photosynthetic eukaryotic organisms. They are distinguished from other eukaryotic protists by their ability to move at some stage of their life cycle and by their lack of cell walls. Some protozoa are free living while some are parasitic. Some protozoa form colonies, in a colony, the individual cells are joined by cytoplasmic thread or embedded in a common matrix, hence colonies of protozoa are essentially a cluster of independent cells. The study of protozoa is called Protozoology. This unit examines the general characteristics of protozoa, the morphology, occurrence, reproduction and economic importance of protozoa. General Characteristics of Protozoa They are unicellular, non-photosynthetic microorganisms. They are predominantly microscopic in size. They occur generally as single cells. They lack cell walls. They have ability to move at some stages of their life cycle, as many are motile. The majority of protozoa are between 5 and 250μm in diameter. They occur in colonies with each colony having independent individual cells. Protozoa may be divided into free-living forms and those living on or in other organisms. Occurrence/Distribution Protozoa are found in all moist habitats. They are common in the sea, in soil and freshwater. Free-living protozoa have even been found in the Polar Regions and at very high altitudes. Parasitic protozoa may be found in association with most animal groups. Most protozoa survive dry conditions by the formation of a resistant cyst or dormant stage. Ecology From the ecological standpoint, protozoa may be divided into free-living forms and those living on or in other organisms. The latter group is referred to as the symbiotic protozoa. Some of the symbiotic ones are parasitic and may cause disease. Others such as those found in the gut of the termite are beneficial to the host (live in a mutualistic association). a. Free-Living Protozoa - Free-living protozoa are found in a variety of habitats. The factors which influence the distribution and number of free-living protozoa  in a habitat are: moisture, temperature, light, available nutrients, and other physical and chemical conditions. b. Symbiotic Protozoa - This is a type of co-existence between protozoa and other organisms which differ in many ways and include: sm: In which the host is neither injured nor benefitted but the commensal (protozoa) is benefitted, e.g. the protozoa living in the lumen of the alimentary tract. Mutualism in which some flagellates are present in the gut of termites and help to digest the woody materials eaten by termite to a form which can be used by the host cells. If deprived of these flagellates, the termite dies, if the flagellates are removed from the termite gut, they also die. Some protozoa are parasites, they live at the expense of other organisms, and an example is Plasmodium which is a parasite of man and causes malaria in man. Morphology of Protozoa The size and shape of these organisms show considerable variable. Like all eukaryotic cells, the protozoan cell also consists of cytoplasm, separated from the surrounding medium by a special cell envelope, and the nucleus or nuclei. Cytoplasm - The cytoplasm is a more or less homogeneous substance consisting of globular protein molecules loosely linked together to form a three- dimensional molecular framework. Embedded within it are the various structures that give protozoan cells their characteristic appearance. Submicroscopic protein fibrils (fibrillar bundles, myonemes, and microtubules) are groups of parallel fibrils in the cytoplasm. Protozoan contractility is probably due to these fibrils. In several forms of protozoa, pigments are diffused throughout the cytoplasm. These are numerous. They can be green, brown, blue, purple or rose. In the majority of protozoa, the cytoplasm is differentiated into the ectoplasm and the endoplasm. The ectoplasm is more gel-like and the endoplasm is more voluminous and fluids, but the change from one layer to another is gradual. Structures are predominantly found in the endoplasm. Like other eukaryotic cells, protozoa have membrane systems in the cytoplasm. They form a more or less continuous network of canals and lacunae giving rise to the endoplasmic reticulum of the cell. Other structures in the cytoplasm include ribosomes, Golgi complexes or dictyosomes (piles of membranous sacs) mitochondria, kinetosomes or blepharoplasts (intracytoplasmic basal bodies of cilia or flagella), food vacuoles, contractile vacuoles, and nuclei.  Nucleus - The protozoan cell has at least one eukaryotic nucleus. Many protozoa, however, have multiple nuclei (e.g. almost all ciliates throughout the greater part of the life cycle). The protozoan nuclei are of various forms, sizes, and structures. In several species, each individual organism has two similar nuclei. In the ciliates two dissimilar nuclei, one large (macronucleus) and one small (micronucleus) are present. The macronucleus controls the metabolic activities and regeneration processes; the micronucleus is concerned with reproductive activity. Cysts - Many protozoa form resistant cysts at certain times of their life cycle. As indicated before, these cysts are able to survive adverse environment conditions such as desiccation, low nutrient supply, and even anaerobic. In parasitic protozoa, the developmental stages are often transmitted from host to host within a cyst. Other kinds of cysts (e.g. reproductive) are also known. Cysts have four basic functions, namely; protect against unfavorable conditions; serve as site of multiplication; assist in attachment to surfaces such as hosts; transmission stage from host to host. Asexual reproduction in some ciliates and flagellates is associated with cyst formation. Sexual reproduction of sporozoa invariably results in a cyst. Locomotive Organelles Protozoa may move by three types of specialized organelles: pseudopodia, flagella and cilia. In addition, a few protozoa without such organelles can carry out a gliding movement by body flexion. Pseudopodia - A pseudopodium is a temporary projection of part of the cytoplasm of those protozoa which do not have a rigid pellicle. Pseudopodia are therefore characteristic of the amoebas (Sarcodina). These organelles are also used for capturing food substances. Flagella - The flagellum is an extremely fine filamentous extension of the cell. As a rule, the number of flagella present in an individual protozoan varies from one to eight; one or two is the most frequent number. A flagellum is composed of two parts; an elastic filament called an axoneme and the contractile cytoplasmic sheath that surrounds the axoneme. Cilia - are fine and short threadlike extensions from the cell. In addition to their locomotive function, it also aids in the ingestion of food and serve often as a tactile organelle. They may be uniform in length, or may be of different lengths depending on their location. Generally, cilia are arranged in  longitudinal, oblique, or spiral rows, inserted either on the ridges or in the furrows. Feeding Structure Food-gathering structures in the protozoa are diverse and range from the pseudopodia of amoebas through the tentacular feeding tubes of suctorians to the well- developed “mouths” of many ciliates. Amoebas gather food by means of pseudopodial engulfment. In ciliates, the cytostome is the actual opening through which food is ingested. An oral groove is an indentation in the pellicle of certain ciliates. It guides food toward the cytostome and acts as a concentrating device. The addition of membranelles to the oral groove makes it a peristome. Nutrition Nutrition in protozoa is heterotrophic. They obtain cellular energy from organic substances such as proteins. Protozoa engulf and ingest their food sources. Reproduction Protozoa general multiply by asexual reproduction. Many protozoa are able to carry out both asexual and sexual processes. Some parasitic forms may have an asexual phase in one host and a sexual phase in another host. Asexual Reproduction - It occurs by simple cell division, which can be equal or unequal – the daughter cells are of equal or unequal sizes, respectively. If two daughter cells are formed, then the process is called binary fission. If many daughter cells are formed, it is called multiple fission. Budding is a variation of unequal cell division. Binary Fission - The simplest form of binary fission is found in the amoebas. The pseudopodia are withdrawn before the nucleus divides. After the nucleus divides, the organism elongates and constricts in the center in order to form two daughter cells. Multiple Fission - In multiple fission, a single mother (parental) cell divides to form many daughter (filial) cells. Division is usually preceded by formation of multiple nuclei within the mother cell, which then cleaves rapidly to form a corresponding number of daughter cells. Multiple fission is not as widespread as binary fission but it often takes place in addition to the latter process. In ciliates and flagellates, this type of fission is found in relatively few species.  Budding - In protozoology it is often used to describe the varied processes by which sessile protozoa produce motile offspring. That is, the mother cell remains sessile and releases one or more swarming daughter cells. The swarmer differs from the parent cell not only in a lower degree of differentiation but also in the possession of special locomotor organelles. Some form of budding is found in all sessile ciliates and is used to disseminate the species while the mother cell remains in situ. Sexual Reproduction- Various types of sexual reproduction have been observed among protozoa. Sexual fusion of two gametes (syngamy or gametogamy) occurs in various groups of protozoa. They include conjugation, which is generally a temporary union of two individuals for the purpose of exchanging nuclear material, is a sexual process found exclusively in the ciliates. After exchange of nuclei, the conjugants separate and each of them gives rise to its respective progeny by fission or budding. When the gametes (which develop from trophozoites) are morphologically alike, they are called isogametes. When they are unlike in morphology (as well as physiology), they are anisogametes and can be either microgametes or macrogametes. Economic Importance Protozoa are important links in the food chain of communities in aquatic environment where they act as primary consumers. They are used in biological treatment of sewage or industrial effluents. Some protozoa cause disease in mammals including man. They are important research organisms for biologists and chemists. Figure 10. Schematic illustration of the structure of amoeba and paramecium  LET’S REMEMBER! To summarize our lessons for this module and to give you further details of the discussion, here are the synopsis of all lessons (L1-L5) which you have read. 1. Bacteria are small, simple prokaryotic cells that have defined shapes and organelles which perform definite functions. They are capable of independent living and existence. As prokaryotic single-celled organisms, they lack membrane- bound organelles. They are very small, with sizes ranging from 0.5 to 1.0nm in diameter. The typical shapes of bacteria are cocci (spherical), bacilli (rod), vibrio, spirila and spirochetes. Having complex cell components, the structures external to its cell wall includes flagella, pili, capsules, sheaths, prosthecae and stalks. The cell wall is rigid structure made up of peptidoglycan that gives shape to bacterial cells. Bacteria are classified based on differences in the composition of cell wall as determined by the Gram stain techniques. On the other hand, the structures internal to the bacterial cell include cytoplasmic membrane, protoplast, the cytoplasm, the nuclear material, spores and cysts. Based on source of energy bacteria can be classified as phototrophs and chemotrophs. Based on source of carbon for nutrition, bacteria can be classified as heterotrophs and chemotrophs. Based on oxygen requirement, bacteria are classified as aerobic, anaerobic and facultative anaerobe. Bacteria reproduce asexually by transverse binary fission. Some bacteria are economically important, but some are pathogenic. (L1) 2. Fungi are eukaryotic spore bearing organisms that lack chlorophyll and reproduce both asexually and sexually. They are widespread in environment and found wherever water suitable organic nutrients and an appropriate temperature occur. Many are terrestrial, some are aquatic while others are parasitic in living hosts. The body or vegetative structure of a fungus is called thallus. Fungi may be grouped into molds or yeasts based on the development of the thallus. Yeasts are unicellular fungi that have a single nucleus and reproduce either asexually by budding or asexually by spore formation. A mold is made up of long branched thread-like filament called hyphae that form a tangled mass called mycelium. Some fungi are saprophytes and grow best in moist dark habitats. They are usually aerobic but some types of yeasts are facultative. Asexual reproduction occurs in fungi by the production of specific types of spores which are easily dispersed. Sexual reproduction occurs by the fusion of hyphae or cells of different mating types. (L2) 3. Viruses are simple acellular entities that can only reproduce within living cells. A virus is made up of a central genetic nucleic acid molecule which could be DNA or RNA surrounded by a protein called capsid. Capsids are large macromolecular structures that self-assemble from many copies of one or a few types of proteins. Viruses range in size from 10 to 400 nm in diameter and can only be viewed with electron microscope. Viral nucleic acid can either be single stranded or double stranded DNA or RNA. Some viral genomes are circular while some are linear. Viral reproduction can be divided into five steps, namely:  attachment, entry into host, synthesis of viral nucleic acid and proteins, self- assembly of virions and release from host. Viruses can be cultivated using tissue cultures, embryonated eggs, bacterial culture and other living hosts. Viral purification involves getting the viral particle in its pure state and involves techniques such as differential and gradient centrifugation, precipitation, denaturation or digestion of contaminants, and can be counted directly with the transmission electron microscope or indirectly by the hemagglutination assay. (L3) 4. The algae are photosynthetic eukaryotic microorganisms. They are found in many places on Earth including ocean, lakes, ponds, streams, moist soils, rocks, tree barks, ice and hot springs. Algae may be unicellular or multicellular, have cell wall, a discrete nucleus starch grains, oil droplets, vacuoles chlorophyll and other pigments. They reproduce asexually by binary fission and sexually by fusion of gametes to form a zygote. Algae are primary producers in most aquatic food chains. Commercially, they are sources of agar, alginic acid and carrageenan. (L4) 5. Protozoa are unicellular non-photosynthetic microorganisms that lack cell wall and have ability to move at some stages of their life. Protozoa are normally found in moist habitats. They may be free living found in various habitats or symbiotic found in co-existing with other organisms. The size and shape of protozoa vary considerable and the cell consists of the cytoplasm (separated from the surrounding medium by an envelope) and the nucleus or nuclei. Locomotive organelles in protozoa include pseudopodia, cilia and flagella. Its reproduction is mainly asexual, however many are able to carry out both asexual and sexual reproduction. The asexual reproduction in protozoa is through binary fission, multiple fission and budding. While sexual reproduction involves the fusion of two gametes. Protozoa are primary consumer in food chain, in aquatic environment. They are used to degrade biological and industrial effluents. They also cause disease of human and other animals. (L5) HOW MUCH HAVE YOU LEARNED! Let’s answer the following guide questions. Good luck! 1. How are bacteria differs in terms of morphology, cellular structure, respiration, nutrition and stainability? Make a tabular matrix to summarize your answer. 2. Fungi used to develop into two morpholgies, the yeast and mold stages. How do they differ from one another? 3. Viral infection may occur either by lytic or lysogenic mode. In terms of mechanism and effect to infected host cell, how do they occur? You may explain by illustrating the infection process. 4. Distinguish the significant characteristics of algae from the rest of the microoganisms. Explain briefly the aspects of its biological classification. 5. Amoeba and paramecium are two highly known representative species of the protozoan. Classify them bascallt according to morphology/structure, locomotion, and reproduction.  ANY FEEDBACK! For your feedback to this module, you may write your concern inside the box and let your professor know. REFERENCES Ilusanya, O.A.F. 2011. Course Module for General Microbiology (BIO 217). National Open University of Nigeria, Victoria Island, Lagos. 208 pp. Karp, G. 2013. Cell and Molecular Biology, Concepts and Experiment 7 th Edition. John Wiley and Sons, Inc., USA. 874 pp. www.google.com (source of images for Figures 2-10)