Microbiology Lecture Notes: Bacterial Size, Shape & Arrangement

LECTURE NOTE 2- PROF. (MRS) A. O. OLUDURO'S ASPECT ================================================== Different Size, Shape and Arrangement of Bacterial Cells ======================================================== Size of Bacterial Cell ---------------------- The average diameter of spherical b...

LECTURE NOTE 2- PROF. (MRS) A. O. OLUDURO'S ASPECT ================================================== Different Size, Shape and Arrangement of Bacterial Cells ======================================================== Size of Bacterial Cell ---------------------- The average diameter of spherical bacteria is 0.5-2.0 µm. For rod-shaped or filamentous bacteria, length is 1-10 µm and diameter is 0.25-1.0 µm. - *E. coli* , a bacillus of about average size is 1.1 to 1.5 µm wide by 2.0 to 6.0 µm long. - Spirochaetes occasionally reach 500 µm in length and the cyanobacterium - *Oscillatoria* is about 7 µm in diameter. - The bacterium, *Epulosiscium fishelsoni* , can be seen with the naked eye (600 µm long by 80 µm in diameter). - One group of bacteria, called the Mycoplasmas, have individuals with size much smaller than these dimensions. They measure about 0.25 µ and are the smallest cells known so far. They were formerly known as pleuropneumonia-like organisms (PPLO). - *Mycoplasma gallicepticum, w*ith a size of approximately 200 to 300 nm are thought to be the world smallest bacteria. - *Thiomargarita namibiensis* is world's largest bacteria, a gram-negative Proteobacterium found in the ocean sediments off the coast of Namibia. Usually it is 0.1---0.3 mm (100---300 µm) across, but bigger cells have been observed up to 0.75 mm (750 µm). - Thus a f *E. coli* , a bacillus of about average size is 1.1 to 1.5 µm wide by 2.0 to 6.0 µm long. - Spirochaetes occasionally reach 500 µm in length and the cyanobacterium - *Oscillatoria* is about 7 µm in diameter. - The bacterium, *Epulosiscium fishelsoni* , can be seen with the naked eye (600 µm long by 80 µm in diameter). - One group of bacteria, called the Mycoplasmas, have individuals with size much smaller than these dimensions. They measure about 0.25 µ and are the smallest cells known so far. They were formerly known as pleuropneumonia-like organisms (PPLO). - *Mycoplasma gallicepticum, w*ith a size of approximately 200 to 300 nm are thought to be the world smallest bacteria. - *Thiomargarita namibiensis* is world's largest bacteria, a gram-negative Proteobacterium found in the ocean sediments off the coast of Namibia. Usually it is 0.1---0.3 mm (100---300 µm) across, but bigger cells have been observed up to 0.75 mm (750 µm). Thus a few bacteria are much larger than the average eukaryotic cell (typical plant and animal cells are around 10 to 50 µm in diameter). Shape of Bacterial Cell ----------------------- The three basic bacterial shapes are coccus (spherical), bacillus (rod-shaped), and spiral (twisted), however pleomorphic bacteria can assume several shapes. i. **Spherical (coccus** for a single cell**)-** are round cells, sometimes slightly flattened when they are adjacent to one another. **The Spherical bacteria (cocci) may occur either singly (micro or monococci) or in pairs (diplococcic) or in a group of four (tetracocci) or in chains (streptococci) or in irregular bunches (Staphylococci).** ii. **Rod shaped or cylindrical (bacillus** for a single cell**)- Rod shaped bacteria occur usually singly but may occasionally be found in pairs (diplobacilli) or in chains (streptobacilli), and** iii. **Spiral or spirilla (Spirillum** for a single cell**)-** are curved bacteria which can range from a gently curved shape to a corkscrew-like spiral. Many spirilla are rigid and capable of movement. A special group of spirilla known as spirochetes are long, slender, and flexible. https://microbiologyinfo.com/wp-content/uploads/2015/05/Shape-of-Bacterial-Cell.gif **Shape of bacterial cell**  ------------------------------------------------------------------------------ Arrangement of Cocci -------------------- Cocci bacteria can exist singly, in pairs (as diplococci ), in groups of four (as tetrads ), in chains (as streptococci ), in clusters (as stapylococci ), or in cubes consisting of eight cells (as sarcinae). Cocci may be oval, elongated, or flattened on one side. Cocci may remain attached after cell division. These group characteristics are often used to help identify certain cocci. 1. Diplococci ------------- The cocci are arranged in pairs. Examples: *Streptococcus pneumoniae, Moraxella catarrhalis, Neisseria gonorrhoeae,* etc. 2. Streptococci --------------- The cocci are arranged in chains, as the cells divide in one plane. Examples: *Streptococcus pyogenes, Streptococcus agalactiae* 3. Tetrads ---------- The cocci are arranged in packets of four cells, as the cells divide in two plains. Examples: *Aerococcus, Pediococcus and Tetragenococcus* 4. Sarcinae ----------- The cocci are arranged in a cuboidal manner, as the cells are formed by regular cell divisions in three planes. Cocci that divide in three planes and remain in groups cube like groups of eight. Examples: *Sarcina ventriculi, Sarcina ureae, etc.* 5. Staphylococci ---------------- The cocci are arranged in grape-like clusters formed by irregular cell divisions in three plains. Examples: *Staphylococcus aureus* Arrangement of Bacilli ---------------------- The cylindrical or rod-shaped bacteria are called 'bacillus' (plural: bacilli). ### 1. Diplobacilli Most bacilli appear as single rods. Diplobacilli appear in pairs after division. Example of single Rod: *Bacillus cereus*\ Examples of diplobacilli: *Coxiella burnetii, Moraxella bovis, Klebsiella rhinoscleromatis,* etc. ### 2. Streptobacilli The bacilli are arranged in chains, as the cells divide in one plane. Examples: *Streptobacillus moniliformis* ### 3. Coccobacilli The bacilli bend at the points of division following the cell divisions, resulting in a palisade arrangement resembling a picket fence and angular patterns that look like Chinese letters. Example: *Corynebacterium diphtheriae* Arrangement of Spiral Bacteria ------------------------------ Spirilla (or spirillum for a single cell) are curved bacteria which can range from a gently curved shape to a corkscrew-like spiral. Many spirilla are rigid and capable of movement. A special group of spirilla known as spirochetes are long, slender, and flexible. 1. Vibrio --------- They are comma-shaped bacteria with less than one complete turn or twist in the cell. Example: *Vibrio cholerae* 2. Spirilla ----------- They have rigid spiral structure. Spirillum with many turns can superficially resemble spirochetes. They do not have outer sheath and endoflagella, but have typical bacterial flagella. Example: *Campylobacter jejuni, Helicobacter pylori*, *Spirillum winogradskyi,* etc. 3. Spirochetes -------------- Spirochetes have a helical shape and flexible bodies. Spirochetes move by means of axial filaments, which look like flagella contained beneath a flexible external sheath but lack typical bacterial flagella. Examples: *Leptospira* species (*Leptospira interrogans*), *Treponema pallidum*, *Borrelia recurrentis*, etc. D. Others Shapes and Arrangements of Bacteria --------------------------------------------- 1. Filamentous Bacteria ----------------------- They are very long thin filament-shaped bacteria. Some of them form branching filaments resulting in a network of filaments called 'mycelium'. Example: *Candidatus* Savagella 2. Star Shaped Bacteria ----------------------- Example: *Stella* 3. Rectangular Bacteria ----------------------- Examples: *Haloarcula* spp *(H. vallismortis, H. marismortui)* 4. Pleomorphic Bacteria ----------------------- These bacteria do not have any characteristic shape unlike all others described above. They can change their shape. In pure cultures, they can be observed to have different shapes. Examples: *Mycoplasma pneumoniae, M. genitalium,* etc. Bacterium  Typical fungal cell. Fungal Hyphae Figure 1 **A TYPICAL PROTOZOAN-EUGLENA**  **A VIRAL PARTICLE- VIRUS** BENEFICIAL AND DELETERIOUS EFFECTS OF MICROORGANISMS Useful effects of microorganisms 1. Bacteria: In industries, they are employed in production of curd, cheese, vinegar, lactic acid, alcohol and even in ripening of tea leaves, etc. 2. Fungi: Some useful fungi are yeast, used to make dough in bakery and alcohol etc. Some fungi are useful for preparing antibiotics. Some mushrooms are useful in making vitamins and organic acids. 3. Algae: Some useful algae are chlorella (produce protein and vitamin), red algae (agar) and brown algae (Iodine and potassium). 4. Protozoa: Some help in the final degradation of waste and sewage while some are symbiotic in nature. 5. Viruses: They are used for scientific research such as in biotechnology, genetic engineering and gene therapy etc.  \ Harmful effects of microorganisms: 1. Bacteria: Cause various diseases such as typhoid, diarrhea, and cholera. 2. Fungi: Cause many diseases in plants and in animals such as rust diseases in plants, fruit rot in apple, red rot in sugar cane and ring worm disease in human beings. 3. Algae: Algal boom in water (rapid growth of algae) causes poisonous effect after they die, which in turn results in the death of aquatic organisms. 4. Protozoa: Cause Amoebic dysentery, pyorrhoea and sleeping sickness etc. 5. Virus: Cause small fox, common cold, influenza, herpes, hepatitis, polio and rabies In addition to the crucial roles that microorganisms play in maintaining all life on earth, they also have made life more comfortable for humans over the centuries. Particularly in biotechnology- which is the application of biology to solve practical problems and produce useful products economically 1.Food Production- yeast in bread making, production of beer from fermenting cereal grains and other fermented drinks., in fermentation of milk to produce yogurt, cheese and butter milk, in probiotics- addition of some bacteria to fermented milk which have been reported to protect against intestinal infections and bowel cancer 2.Bioremediation-This involved the use of microorganisms for the degradation of environmental pollutant-or for the cleanup of polluted environment. Examples; degradation of dangerous chemical pollutants such as polychlorinated biphenyls (PCBs), Dichlorodiphenyltrichlorohane (DDT) and trichloroethylene, a highly toxic solvent used in dry cleaning. Some bacteria can be used for the cleanup of oil spills, to degrade oil, and treat radioactive wastes. 3.Some useful products from bacteria have great commercial value and can be produced at faster and cheaper rates than by being synthesized in the factories e.g Cellulose used in sterol, Hydroxylbutyric acid used in the manufacture of disposable diapers and plastics; Ethanol which is added to gasoline to make it burn cleaner; chemical poisonous to insects; antibiotics used in the treatment of diseases ; and amino acids which are used as dietary supplements 4 Genetic Engineering-This is a process of introducing genes from one organism into an unrelated organism which confer new properties on that organism. Examples of the roles that microorganisms play in biotechnology Include; production of variety of medically important products such as interferon, insulin, human growth hormone, blood clotting factors and enzymes that dissolve blood clots. Microorganisms can be modified to produce vaccines against rabies, gonorrhea, herpes, leprosy, malaria and hepatitis. A bacterium can be used to genetically engineer plants to become resistant to insect attacks and viral diseases, and produce large amounts of β-carotene A bacterium can be used to transfer antibody eliciting genes into bananas which then confer resistance to certain diarrheal diseases Viruses are being studied as a means of delivering genes into humans to correct conditions such as cystic fibrosis, heart disease, and cancer. 5.Genomics- This is the study of bacterial DNA which carries all the information that gives an organism its unique characteristics and ability to carry out the activities that are essential to life on earth