Module 2 - Microbiology PDF

1 Republic of the Philippines BATANGAS STATE UNIVERSITY The National Engineeri...

1 Republic of the Philippines BATANGAS STATE UNIVERSITY The National Engineering University Alangilan Campus Golden Country Homes, Alangilan, Batangas City, Batangas, Philippines 4200 Tel Nos.: (+63 43) 425-0139; (+63 43) 425-0143 loc. 2103 E-mail Address: [email protected] | Website Address: http://www.batstate-u.edu.ph MICROBIOLOGY In our study of microbiology, we will see the smallest of living organisms. These small organisms show the most basic properties of the living condition. In the virus, we find the lack of cellular organization. But the virus still can reproduce under suitable conditions. As our study progresses from the primitive virus, cells increase in complexity. Among these simple organisms, we find cells grouping together to form colonies. Other organisms are organized on the multicellular level. By studying these simple organisms, we will be able to better understand higher forms of life. VIRUSES- LIVING OR NONLIVING? The study of viruses is one of the newest and most interesting fields of biology. This study also raises basic questions about what we mean by the word life. When little was known of viruses, it was much easier to draw a line between the living and nonliving worlds. Then it was found that viruses seem to shift between these worlds, and the line became less clear. Consider a virus alone. It is a particle unlike any other form of nonliving matter. And there are definite links to biochemical processes in the way a virus is organized. Yet the virus itself is not alive. Only in the presence of a living system in a cell does it show signs of life and then it seems very much alive. Could viruses be living at some times and nonliving at others? It all depends on how we define life, and biologists have yet to agree on such a definition.  2 Whether viruses are living or nonliving, they belong in our Unit on microbiology. If nonliving, their effects on cells are different from those of any other nonliving material. If living, they are clearly the most basic organisms-life at the molecular level. WHAT ARE VIRUSES LIKE? At the mention of the word virus, you probably think of an agent of disease. Many viruses do cause diseases, polio, smallpox, influenza, rabies, and the common cold. All in all, more than 300 viruses are known to cause diseases in certain organisms. Until recently, in fact, scientists thought that all viruses were pathogenic, or able to produce disease. However, many viruses are now known that seem to be harmless. Virus particles are not cells. They are subcellular or organized below the level of the cell. A virus has no nucleus, no cytoplasm, and no surrounding membrane. It is larger than a molecule but much smaller than the smallest cell. We call viruses filterable viruses because they pass through the very small pores of filters used to separate bacteria from fluids. Only the largest viruses are visible through a light microscope. Thus, little was known of the structure of viruses before the electron microscope came into use. With this instrument, even the smallest viruses have been photographed. We are now familiar with the forms and sizes of many viruses. Viruses occur in many shapes. Some are like needles or rods, others are round. Some are shaped like cubes or like bricks. Still, others have oval or many-sided heads and slender tails. As for size, we measure viruses in millimicrons (mu). A millimicron is one-millionth of a  3 millimeter. To understand how very small this is, consider that the smallest bacteria range from 500 to 750 milli microns. Such bacteria appear only as tiny specks through a light microscope at high power. Still, these bacteria are large compared to viruses. THE DISCOVERY OF VIRUSES Scientists had learned to prevent certain virus diseases long before anyone knew that viruses existed. Edward Jenner gave the first vaccination for smallpox in 1796. About a century later Louis Pasteur developed his vaccine for rabies. Yet neither of these men had ever seen or heard of viruses. Even into the twentieth century, viruses themselves remained unknown, though many scientists were studying virus diseases One such scientist was the Russian biologist Dmitri Iwanowski. In his work, important though it was, we can see some of the reasons viruses were not found sooner. In 1892, Iwanowski was studying a virus disease of tobacco plants known as tobacco mosaic. The word mosaic refers to a pattern of light green and yellow areas that appears on the diseased tobacco leaves. Iwanowski first squeezed fluid from diseased leaves, then rubbed this fluid onto healthy plants. The healthy leaves soon showed the mosaic pattern of the disease. Iwanowski repeated the experiment. But this time, he passed the fluid through a filter with pores small enough to remove all bacteria. The microscope showed no bacteria or other bodies that might cause disease in this fluid. But when the fluid was rubbed on healthy plants, it still caused the disease. These results puzzled Iwanowski and no wonder. In his day, bacteria were thought to be the smallest possible agents of disease. The viruses, of course, were far too small to be seen through his light microscope. He could only assume that some invisible poison, given off by the bacteria, had passed through the filter. Six years later, the Dutch botanist Martinus Beijerinck repeated Iwanowski's work. He reached a different conclusion. He believed that the fluid must contain some invisible agent smaller than the smallest bacteria. He named this unknown agent virus, a Latin word meaning "poison."  4 Still, it was not until 1935 that the virus itself was found. The discoverer was Dr. Wendell Stanley. Stanley ground and removed the fluid from more than a ton of diseased tobacco leaves. From this fluid, he obtained about a teaspoonful of needlelike crystals. Stored in a bottle, these crystals seemed to have no life. Yet when they were put in water and rubbed on tobacco leaves, they produced the mosaic disease. Stanley had isolated the tobacco mosaic virus. For this work, he received the Nobel prize in chemistry in 1946. OTHER PROPERTIES OF VIRUSES The living condition is a state of constant chemical activity. This activity takes several forms-growth, respiration, and so on. These processes go on constantly in all living cells. On its own, a virus shows no such activity. Only when in direct contact with the content of a specific host cell does a virus show any signs of life. The host cell is any cell attacked by a virus. Even then, its activity is limited and is made possible only by the activity of the cell itself. Removed from the cell, the virus again loses all signs of life. However, it still could infect a cell. A virus cannot reproduce on its own. That is, it cannot divide like a cell and produce new viruses. To reproduce, a virus must invade a host cell and take control of the cell's activity. Biologists are not sure how this is done, and different viruses may affect cells in different ways. However, one hypothesis has received support. According to it, the virus changes the enzyme patterns that control protein synthesis in the cell. The virus does this by injecting its own DNA or RNA into the host cell. This change causes the cell to build viruses rather than normal cell structures. If this hypothesis is correct, the virus acts in much the same way as a gene. Could a virus be a gene (or group of genes) that has no "home" until it invades a cell? On the other hand, many viruses are themselves affected by the environment in which they grow. For example, the rabies virus is grown in cells of the brain and spinal cord of a dog. If so, the strength, or virulence (VIR-uh-lenss), of the virus increases for dogs and human beings. If the virus is grown in rabbits, it loses virulence for people and dogs but gains virulence for rabbits. Viruses also vary by mutation. More than fifty mutant strains of the tobacco mosaic virus have been discovered. These strains differ in virulence and in the symptoms, they produce in the host plant. Such variations may explain why some epidemics of the same disease are worse than others. Perhaps the virus gains in virulence as the disease is passed from person to person. Or perhaps a mutant strain with greater virulence is involved. CLASSIFICATION OF VIRUSES Viruses in general invade only specific kinds of cells. For this reason, we classify viruses according to their host organisms. This system gives us the following types: Bacterial viruses invade the cells of bacteria. Plant viruses are found in the cells of seed plants. Human and animal viruses, invade human and animal cells. The relationship between virus and host is much more specific than these large groups indicate. Bacterial viruses invade only certain kinds of bacteria. A plant virus may invade only a specific plant and only specific cells, such as leaf cells, within that plant. An animal virus may  5 become active only in certain tissue cells, such as skin cells, in a specific animal. Some viruses are still more specific. Polio viruses attack only one kind of nerve cell in the brain and spinal cord. The mumps virus infects only one pair of salivary glands, it never invades the other pairs. BACTERIOPHAGES Much of what we know about viruses has come from a study of bacterial viruses, also known as phages (FAH-jiz). Phages look a bit like tadpoles. They have round or many-sided heads, and slender tails with several fibers for attaching to bacteria. The coat of a phage is made up of protein. The core is usually DNA, but some phages contain RNA instead. The first discoveries about phages were made in England in 1915. Scientists had noticed something strange that happened in cultures of a certain bacterium. Small circles appeared in which the bacteria had been killed. These circles, or plaques, spread until the whole colony of bacteria was destroyed. It was also found that the unknown agent that destroyed the bacteria could be transferred to other colonies with a needle. The actual agent that killed the bacteria was not discovered for several years. But this agent was given the name we still use today -bacteriophage, or "bacteria eater." HOPES FOR MEDICAL USE OF PHAGES Many diseases are caused by bacteria. Couldn't we cure these diseases by using virulent phages to destroy the bacteria? At one time, there was great hope that this could be done. But further studies have run into many problems.  6 For example, some diseases infect tissues deep in the body. It may be difficult to introduce a phage into such tissues. In other diseases, the infection is very widespread. Thus, the phages may not be able to reach enough bacteria to be helpful. Still, another problem is that the human tissue environment may not be suited for phage action. For these and other reasons, we are less hopeful today about using phages as major weapons against disease. HUMAN AND ANIMAL VIRUSES Many familiar diseases of human beings and animals are caused by viruses. In most cases, the virus invades only specific tissues. Symptoms of virus diseases are as different as the viruses that cause them. However, most virus infections interfere with normal cell activity and may damage or destroy tissue. We have already mentioned several virus diseases that affect human beings. To this list, we could add chicken pox, measles, warts, virus pneumonia, yellow fever, cold sores, fever blisters, and many others. A victim who recovers from certain virus diseases, such as chicken pox, becomes immune to the disease. In other cases, such as the common cold, the victim does not become immune. CAN VIRUSES CAUSE CANCER? Much recent cancer research has focused on viruses. Several vi. ruses may be linked to certain types of human cancer. Results of experiments with animals have been encouraging. For example, a form of leukemia can be caused in mice by injecting them with a certain virus. By similar methods, more than twenty kinds of malignant tumors have been produced in mice, guinea pigs, and hamsters. In 1975, Doctors Temin, Baltimore, and Dulbecco received the Nobel prize for their work showing that cancer viruses make an enzyme that affects human DNA. This was a major step in discovering how viruses might play a role in cancer. If scientists can find viruses that do cause human cancers, they may also find a way to prevent or cure some cancers. BACTERIA AND RELATED ORGANISMS BACTERIA- THE MOST COMMON FORM OF LIFE As our study moves from viruses to bacteria and their relatives, we will see living cells at their simplest level. In fact, bacteria may have been the first form of life on earth. Many biologists believe that bacteria existed long before the first photosynthetic green plants. These early bacteria may have taken energy from iron, sulfur, and nitrogen compounds rather than from the sun. Geologists think that the great deposits of iron ore we use today resulted from bacterial action billions of years ago. Later, green plants arose and began building up stores of organic compounds. New kinds of bacteria developed that used these compounds as food. Still, other bacteria invaded the tissues  7 of the plants themselves. When animals came into being, bacteria developed that could live off them as well. Bacteria have survived through the ages. Today, they are the most common life form on our planet. Too small to be seen by the naked eye, they live almost everywhere. There are bacteria in the air, water, soil, our foods, and the bodies of all plants and animals. In fact, any environment that can support life has its population of bacteria. LOUIS PASTEUR AND THE BIRTH OF BACTERIOLOGY In any science, a few names stand out above all others. In biology, one such name is Louis Pasteur. We have already mentioned Pasteur's vaccine for rabies and his defeat of the theory of spontaneous generation. Even if he had done nothing else, he would still be remembered for these works. Yet, in fact, they represent only a small part of his total achievement. Born in France in 1822, Pasteur began his scientific career as a chemist. In 1854, he was appointed professor of chemistry and dean at the University of Lille. This location turned out to be quite important. The city of Lille was a center for making alcohol by fermentation of the juice of sugar beets. And it was Pasteur's studies of fermentation that opened a whole new world to the science of biology. With his microscope, Pasteur studied the juice that was fermenting normally. He saw many yeast cells spread through the liquid. Over several hours, more yeast cells grew. As they did so, the alcohol content of the juice rose. Were the yeasts producing the alcohol? In trying to learn the answer, Pasteur next examined the sour juice. This juice contained no alcohol but lactic acid. Further, instead of yeasts, it contained smaller, rod-shaped bodies. These bodies moved and seemed to be alive. They increased in number as the yeasts had. As these rod-shaped bodies increased, the lactic acid content of the juice also increased. These discoveries led Pasteur to begin a much more complete study of fermentation After three years, he set up a small laboratory in Paris. There he finally proved his theory. Fermentation does result from the action of microorganisms, and the products formed depend on the organisms involved. Yeasts produce alcohol Lactic acid is formed by bacteria. Pasteur did not end his studies of bacteria here. Much greater discoveries lay ahead. Perhaps the most important was his germ theory, which changed the course of modern medicine. According to this theory, bacteria could not only affect fermentation but could cause diseases. Modern bacteriology and microbiology both springs largely from Pasteur's work. WHAT ARE BACTERIA? Since Pasteur's time, bacteria have been thought of either as plants or as animals. Recently, however, biologists have placed them in the kingdom Protista. Along with their relatives, bacteria make up the protist phylum Schizomycophyta (SKIZZ-uh-MY-KAH fuh-tuh). This name means "fission fungi." Compared with a virus, a bacterium is quite large. A single bacterium can contain as many as 300 phage viruses. But compared with the cells of most other organisms, bacteria are very small.  8 Like viruses, bacteria are measured in millimicrons (mµ). Sphere-shaped bacteria range from about 500 mµ to 1,500 mµ in diameter. Rodshaped bacteria may be from 200 to 2,000 mµ thick and from 500 to 10,000 mµ long. If these figures mean little to you, consider that several thousand bacteria could fit into the period at the end of this sentence. At high power (430x), a laboratory microscope will show some bacteria and give you an idea of their shapes. However, magnification of 1,000× to 1.500x is needed to see them clearly. No light microscope is strong enough to show most cell structures of bacteria. For this, an electron microscope must be used. FORMS OF BACTERIA While bacteria vary in size, their cells are of three basic shapes. Some bacteria tend to live as single cells. Others tend to remain attached after cell division, forming colonies. These colonies, too, have certain basic shapes. The shapes of bacteria and their colonies are as follows: coccus (plural, cocci): sphere-shaped cells o diplococcus: cells often joined in pairs or short filaments o staphylococcus: clusters of cells o streptococcus: filaments, or strings, of cells o tetrad: four cells arranged in a square o sarcina: cubes or similar groups of cells bacillus (plural, bacilli): rod-shaped cells o diplobacillus: cells in pairs o streptobacillus: cells joined end to end, forming a filament  9 spirillum (plural, spirilla): cells shaped like bent rods or corkscrews. STRUCTURE OF BACTERIAL CELLS In some ways, bacteria are much like other organisms. A bacterium has a cell wall that gives it its shape. Within this wall, a thin plasma membrane surrounds the cytoplasm. There is no nuclear membrane, but a nuclear area near the center of the cell. This area contains chromatin bodies made up of DNA in the form of genes. Some biologists think that these bodies make up a single chromosome. Mitosis does not occur in bacteria, but the chromatin bodies do divide when the cell splits. Thus, each daughter cell receives an equal amount of DNA. Many bacteria have granules of stored food and other substances spread through the cytoplasm. A few also contain vacuoles of water and dissolved materials. Respiratory enzymes are usually found on mitochondria in cells, but bacteria have no mitochondria. Instead, the respiratory enzymes seem to be concentrated on or near the cell membrane.  10 Another important difference between bacteria and other cells is the slime layer that surrounds a bacterium. Lying outside the cell wall, this slime may protect the bacterium and help it to stick to a food supply or host cell. The slime layer varies in thickness in different bacteria. Some have a thick slime layer called a capsule. The pneumonia bacterium has such a capsule. In fact, the capsule is a key to the virulence of the pneumonia organism. Forms with the capsule produce serious infections. Forms without the capsule produce milder infections or even none at all. It may be that the capsule protects the bacteria against the natural defenses of the victim's body MOVEMENT OF BACTERIA Certain bacillus and spirillum bacteria move by means of flagella (fluh-JELL-uh), These threadlike whips extend from the cell membrane and are used in "swimming" through water and other fluids. In some bacteria, flagella are found as single strands or tufts of strands at either end of the cell. In others, the flagella are all around the cell. Flagella are visible only when treated with special stains. Through a light microscope at high power, they look like tiny threads. The electron microscope shows that they are actually part of the cytoplasm, which extends through openings in the cell wall. They are made up mainly of strands of protein molecules. In some ways, these strands are muscle fibers. Thus, the basis for muscle contractions in animals may lie in the beating flagella of bacteria. You can see the movement of bacteria through the microscope. True movement, motility, by means of flagella is a quivering, twisting motion. It should not be confused with the flowing or bouncing motion known as the Brownian movement. Brownian movement is seen mainly in very small bacteria, especially coccus forms. It is caused by the bumping of molecules and other moving particles against the bacteria. CONDITIONS FOR GROWTH OF BACTERIA Bacteria do not have to remain active in order to survive. They can lie dormant, or inactive when conditions are not right for growth and other normal activity. When conditions improve, they may become active again, growing and reproducing very rapidly. The conditions most important to bacteria for normal activity are as follows:  11 Temperature. Many bacteria are most active at fairly warm temperatures, about 26° C to 38 C. Those that cause human infections grow best at 37° C- normal human body temperature However, some bacteria grow best at temperatures as low as or C. the freezing point. These forms occur mainly in the far north, the ocean depths, and at very high altitudes. Still, other bacteria are active at temperatures as high as 85° C. They are found in hot springs and in the hot environment of decaying organic matter such as sewage. Moisture. Active bacteria are about 90 percent water. In dry surroundings, water loss makes the cells inactive. Dryness over a long period will kill most species. Darkness. Most bacteria grow best in the dark. Sunlight may slow down growth. Ultraviolet rays actually kill most bacteria. This is why special lamps that give off such rays are used to sterilize hospital operating rooms. Food. Bacteria vary greatly in terms of their food needs. Some forms require very specific foods. Most pathogenic forms, for example, need living tissues or substances much like their own in chemical makeup. Many other bacteria are less specific and can live on a wide range of foods. NUTRITION IN BACTERIA Some bacteria can build their own food compounds from carbon dioxide and other inorganic substances. Organisms that are able to make their own food from inorganic matter are called autotrophs. Energy is needed in this process. In some cases, energy is obtained by breaking down inorganic compounds of iron, sulfur, or nitrogen. We noted that this process is called chemosynthesis. Further, a few bacteria carry on a form of photosynthesis. Most bacteria, however, cannot build their own foods. Instead, their nutrition must rely on organic compounds formed by other organisms. Organisms that depend upon other living things for food are called heterotrophs. For this reason, such bacteria are in direct competition for food with human beings and other animals. Some of these bacteria are saprophytes. That is, they use nonliving or dead organic matter for food. Such substances include many food products intended for human use. Bacteria are a major cause of food spoilage. Other bacteria are parasites. These forms invade the bodies of plants and animals and take their food directly from living tissue. The organism invaded by a parasite is called the host. Parasitic bacteria directly harm their hosts. Bacteria secrete powerful enzymes that act as catalysts in chemical changes both inside and outside the bacterial cell. In many of these reactions, food substances are broken down into forms that can be absorbed through the cell membrane. Each enzyme acts on only one kind of food. Enzymes allow saprophytes to break down and use a wide range of substances as foods. Some of these substances, such as wood and other forms of cellulose, are of little use to other organisms. Parasites lack many of the enzymes found in saprophytes. This explains why parasites must be in contact with living tissue, using the enzyme action of the host cells.  12 BACTERIAL REPRODUCTION Bacteria reproduce by binary fission. Under good conditions, they multiply at a very rapid rate. A cell may be formed by division, mature, and begin its own division within as little as 20 minutes. HELPFUL ACTIVITIES OF BACTERIA Not all bacteria are disease-causing, or pathogenic. In fact, most species are harmless, having no direct effect on our lives. Many bacteria are actually helpful, and there are some that we could not live without. Among these are certain bacteria that live in the soil. As you know, green plants are the basis of the food chain upon which almost all life depends. Plants use many substances from the soil in building organic compounds. Where do these substances come from? In great part, they come from other plants and animals that have died. It is here that soil bacteria play an important role. The compounds found in dead plants and animals are too complex for plants to use. These compounds must be broken down into simpler substances. This is exactly what soil bacteria do. We see this breaking down as the process of decay that attacks all dead organisms. In fact, if not for bacteria, every organism that died might lie about for thousands of years with little change. Life on earth is a system made up of many cycles of building up and breaking down. All organisms, from bacteria to human beings, have their place in this system. USES OF BACTERIA IN INDUSTRY Bacteria are important in making many foods and other products of industry. We have  13 already mentioned their function in making alcohol. Vinegar is another product of bacterial action. So is silage, a plant food given to cattle. Because of fermentation by bacteria, silage contains lactic acid. This is of great value in the diet of milk cows. Bacteria are very important in the dairy industry. Some forms must be guarded against carefully. For example, milk may contain bacteria that cause diseases such as tuberculosis. It also contains bacteria that tend to turn the milk sour. Bacteria in milk are killed by pasteurization, a heating process discovered by Louis Pasteur. Some bacteria, however, are very helpful in making dairy products. Different types of "starter" bacteria are used in making and flavoring butter, buttermilk, and milk curds which are the basic form of cheese. Other bacteria are used in flavoring and ripening the many hard and soft cheeses. PRESERVING FOOD FROM BACTERIAL ACTION Bacteria are among our chief competitors for food. We cannot even estimate the amount of food that is spoiled by the activity of bacteria. Most foods would remain edible for years if bacteria were not present or could not reproduce. For this reason, we have developed efficient methods for preserving food. One method involves killing all bacteria present, then sealing the food in a container. Canning is an example of this method. Another method involves keeping foods in conditions under which bacteria reproduce more slowly or cannot reproduce at all. This method includes such processes as cooling or freezing, salt curing, and dehydration. Chemical preservatives may also be used. However, their use has declined somewhat in recent years. Radiation may be an important aid in preserving foods. The foods could be packaged and sealed, then exposed to radiation to destroy all bacteria. What are Protozoans? In older classification systems, the phylum Protozoa was included in the animal kingdom. The members of this phylum were a large number of related one-celled organisms. They were further divided into four classes according to their means of movement. The four different classes are now thought of as four separate phyla.  14 1. Phylum Sarcodina – AMOEBA The genus Amoeba includes several interesting protozoan species. It moves, feels, reproduces, and performs all other life functions. Pseudopodia means "false feet." The motion is a sort of flowing, with new pseudopodia reaching out and ones disappearing back into the cytoplasm. On the basis of this ameboid movement, amoebas are placed in the protist phylum Sarcodina. RESPONSE IN THE AMOEBA Amoebas respond to the conditions around them. Though they have no eyes, they are sensitive to light and seek dim or dark areas. Amoebas also respond to food. Some species of amoeba respond to conditions such as dryness, coldness, or lack of food. Such amoebas become inactive and withdraw into a round mass called a cyst. When conditions improve, the amoebas become active again. REPRODUCTION OF AMOEBAS  15 2. Phylum Ciliophora – Paramecium PARAMECIA- COMPLEX PROTOZOANS In the genus Paramecium, we come to a much more complex form of one-celled life. Species of this genus live mainly in quiet or stagnant ponds. The paramecium cell is shaped like a slipper. Paramecia move by means of hairlike threads of cytoplasm called cilia. These cilia are arranged in rows and beat back and forth like tiny oars. RESPONSE IN PARAMECIA Like amoebas, paramecia have no specialized sense organs. Yet paramecia, too, respond to conditions around them. Except when feeding, the cells swim constantly. when they bump into something, they reverse, turn, and swim off in a new direction. This kind of trial-and-error response is called the avoiding reaction. REPRODUCTION IN PARAMECIA  16 3. Phylum Mastigophora – Euglena A PROTOZOAN THAT SEEMS PART PLANT Several species of the genus Euglena live in ponds and streams. Under the microscope, euglenas have an oval or pear shape. Euglenas were classed as plants in some systems and as animals in others since the cells have certain traits of both kingdoms. Today, they are often placed in the protist phylum Mastigophora. This classification is based on the fact that the euglena swims by means of a flagellum. Euglena has a second method of movement. This euglenoid movement involves a gradual change in the shape of the cell. First, the cell becomes rounded as the posterior part is drawn forward. Then the anterior part is stretched forward, resulting in movement. This contraction and stretching are caused by specialized contractile fibers in the cell. A typical euglena is Euglena gracilis. This cell is surrounded by a thin, flexible pellicle. At the anterior end, a small gullet opening leads into a larger reservoir. A red eyespot is clearly seen near the gullet. This tiny bit of specialized protoplasm is highly sensitive to light. Light is helpful because most species of euglena carry on photosynthesis. Perhaps the most striking feature of the euglena is the presence of many oval chloroplasts spread through the cell. 4. Phylum Sporozoa-Plasmodium PROTOZOAN PARASITES THAT FORM SPORES Protozoans in the protist phylum Sporozoa have no method of movement on their own. These protists are all parasites. They live by absorbing food from the cells or body fluids of a host organism. Many species live in two hosts during their life cycle. A good example of this type of protozoan is Plasmodium. This is the organism that causes malaria in human beings and other warm-blooded animals.  17 Malaria is transmitted by the female Anopheles mosquito. When this mosquito bites a person who has malaria, some of the Plasmodium cells are taken into the mosquito’s stomach. Quinine has been used for many years. Other Pathogenic Protozoans Cysts containing inactive ameba cells are excreted in the feces of infected people. In many areas, sewage disposal methods are crude, and human waste may be used as fertilizer. It is in these areas that amebic dysentery is most common. Two protozoans are known as Trypanosoma cause African sleeping sickness. Trypanosomes live in the blood of many African mammals and insects. They are transmitted to human beings by the bite of the tsetse fly. What are Fungi? Most species of fungi are multicellular, but fungi never form roots, stems, or leaves. Fungi vary in size from microscopic yeasts to mushrooms weighing a half kilogram or more. All fungi are alike in one important way: they all lack chlorophyll. Certain fungi break down the organic remains of dead plants and animals. This process is necessary for keeping the soil fertile.  18 Classifying Fungi We divide the fungi into two protist phyla. The smaller of these is the phylum Myxomycophyta. This phylum includes the slime molds, which lack cell walls. All other fungi have cell walls and are placed in the phylum Eumycophyta. A. Phylum Eumycophyta: ❑ Phycomycetes - the alga-like fungi. ❑ Ascomycetes - the sac fungi. ❑ Basidiomycetes - the club fungi. All true fungi that cannot be placed in one of these classes are grouped in a fourth class: ❑ Deuteromycetes - the imperfect fungi. A. Eumycophyta – The True Fungi These include such types as molds, mildews, blights, yeasts, mushrooms, and others. The bodies of most true fungi are made up of branching filaments called hyphae. The whole mass of hyphae formed by a fungus is known as the mycelium. ❑ Fungi do not contain chlorophyll. ❑ Fungi secrete enzymes into their food supply. ❑ Fungi do not require light, and many grow best in darkness. Moisture and, for most species, warm temperatures are necessary for life. ❑ All true fungi reproduce asexually by forming spores, often in great numbers.  19 1. Phycomycetes- The molds include several kinds of fungi. Some molds are Phycomycetes, other Ascomycetes. One familiar mold is bread mold (Rhizopus nigricans). Related to bread mold are the water molds of the genus Saprolegnia. These Phycomycetes, like bread mold, have tube- like hyphae without cross walls. 2. Ascomycetes ❑ Blue-green molds and powdery mildews. ❑ Molds of the genus Penicillium often form blue- green growths on oranges, lemons, and other fruits. They also appear on bread, meat, leather, and cloth. ❑ Molds of the genus Aspergillus are common on foods, too, forming yellow or black rings. ❑ Both of these genera are Ascomycetes and have hyphae with cross walls. Surface hyphae form branches known as conidiophores. ❑ Powdery mildews attack grapes, roses, clover, apples, wheat, barley, and several other plants. 3. Basidiomycetes  20 ❑ The Basidiomycetes, or club fungi, get their name from the club-shaped basidium found at the end of certain hyphae. ❑ Four groups of fungi make up the class Basidiomycetes. These include rust fungi, smut fungi, mushrooms, and bracket fungi, and puffballs. 4. Deuteromycetes- Sometimes study produces evidence of sexual reproduction in an imperfect fungus. If so, the fungus usually is placed in the fitting class of true fungi. Most imperfect fungi are much like Ascomycetes Phylum Myxomycophyta SLIME MOLDS ❑ They are like giant masses of amoebas. Thus, they might be classed as animals. However, they also form sporangia and spores, like fungi. ❑ Some biologists have called them “slime fungi” or “fungus animals”. This confusion is avoided by placing the slime molds in their own protest phylum, the Myxomycophyta. ❑ The body of a slime mold is called a plasmodium. It is a mass of protoplasm with many nuclei but no cell walls. A plasmodium often appears as a slimy network of living matter.  21 Name: SR-Code: Section: Date: Activity No. 2 Introduction to Microbiology DIRECTIONS: Read and answer the following questions comprehensively. Please refer to the rubric below. 5 4 3 2 1 0 The answer has The answer is The answer The answer has some relevance clear, focused, The answer indicates an many flaws; to the required and indicates an indicates a clear adequate indicates a very concepts; No in-depth understanding understanding minimal indicates a answer understanding of concepts. of concepts but understanding limited of relevant has some of relevant understanding concepts. misconceptions. concepts. of concepts. 1. Define microbiology and explain its significance in understanding higher forms of life. 2. Discuss the reasons for considering viruses living or nonliving. 3. In what way is a temperate phage a potential “seed of destruction”? Explain. 4. Explain the structure and composition of bacteriophages. Discuss their significance in virus research.  22 5. Describe the structure and size of viruses compared to cells. 6. Name five diseases caused by viruses. Explain why many viruses were initially thought to be pathogenic. Diseases Caused by Viruses: 1. ________________________________________ 2. ________________________________________ 3. ________________________________________ 4. ________________________________________ 5. ________________________________________ Reasons for Initial Perception of Viruses as Pathogenic: 7. Explain the discovery of viruses, including the contributions of Dmitri Iwanowski and Wendell Stanley. Discovery of Viruses: ________________________________________ ________________________________________ Contributions of Dmitri Iwanowski: ________________________________________ Contributions of Wendell Stanley: 8. Name three virus diseases that affect human beings. Explain the impact of viruses on normal cell activity. Virus Diseases Affecting Human Beings: ________________________________________ ________________________________________ ________________________________________ Impact of Viruses on Normal Cell Activity:  23 9. Biologists frequently say that understanding the life processes of single-celled protozoans helps them to understand the life processes of complicated organisms like a man. Why is this probably true? 10. Compare methods of locomotion, digestion, and sensitive response in the amoeba, paramecium, and euglena.