Introductory Microbiology (Botany): Monera/bacteria, cyanobacteria, virus, biotechnology in microbiology

Microorganisms (mainly bacteria and fungi) are used in medicine in the following five ways:

1. Production of antibiotics Many antibiotics are obtained from microorganisms. Penicillium notatum and Penicillium chrysogenum (fungi) yield penicillin; Streptomyces species (actinomycetes) yield streptomycin, tetracycline and erythromycin; Bacillus species yield bacitracin. These antibiotics kill or stop the growth of disease-causing bacteria and have saved millions of lives.

2. Production of vaccines Weakened (attenuated) or killed microorganisms, or their toxins, are used to prepare vaccines that give active immunity. Examples: BCG vaccine from attenuated Mycobacterium tuberculosis for tuberculosis, DPT vaccine (killed Bordetella pertussis and tetanus/diphtheria toxoids), oral polio vaccine from attenuated poliovirus, and the smallpox vaccine from vaccinia virus. Vaccination has helped eradicate smallpox and control many epidemics.

3. Production of therapeutic agents (hormones, enzymes and vitamins) Genetically engineered bacteria such as Escherichia coli are used as "factories" to produce human insulin (humulin) for diabetics, human growth hormone, interferon and hepatitis B vaccine. Microbes also produce vitamin B₁₂ (Pseudomonas denitrificans), vitamin B₂ and the enzyme streptokinase (from Streptococcus), which is used to dissolve blood clots in heart attack patients.

4. Production of antibiotics and other drugs from microbial metabolites Besides antibiotics, microorganisms give immunosuppressive drugs such as cyclosporin A (from Trichoderma polysporum), used in organ transplantation to prevent rejection, and statins (from Monascus purpureus), used to lower blood cholesterol. These are life-saving drugs of microbial origin.

5. Role in diagnosis and research Microorganisms are used in diagnostic tests and as model organisms in medical research. For example, Mycobacterium tuberculosis is identified by staining and culture to diagnose tuberculosis; bacteria are used in the Widal test (typhoid), and bacteriophages and bacteria serve as tools in genetic engineering and in studying disease mechanisms, which helps in developing new treatments.

Thus, microorganisms are indispensable in medicine — as sources of antibiotics, vaccines, hormones and drugs, and as tools for diagnosis and research.

(a) Double-stranded DNA

A typical bacteriophage such as T4 has a head containing double-stranded DNA enclosed in a protein capsid.

(b) Mycoplasma

Mycoplasmas are the smallest free-living prokaryotes and have only a plasma membrane, so they are pleomorphic and resistant to penicillin, which acts on cell walls.

(b) Escherichia coli

E. coli is easy to grow and carries plasmids (such as pBR322) used as vectors to carry foreign genes. It is also a common host for recombinant DNA. The other options are protozoa.

(c) Either DNA or RNA

A virus contains only one kind of nucleic acid, never both. Most bacteriophages (like T4) carry DNA, but some (like MS2) carry RNA, so the best general answer is either DNA or RNA.

Harmful and beneficial activities of bacteria (5 marks)

Beneficial activities

1. Agriculture: Rhizobium (in legume root nodules), Azotobacter and Azospirillum fix atmospheric nitrogen and enrich the soil. Decomposer bacteria recycle dead matter into nutrients.
2. Food and dairy: Lactobacillus converts milk into curd, cheese and yoghurt; Acetobacter makes vinegar; bacteria help in retting of jute and curing of tea and tobacco.
3. Medicine: antibiotics such as streptomycin and tetracycline come from Streptomyces; bacteria are used to make vaccines, insulin and growth hormone by genetic engineering (E. coli).
4. Environment: bacteria break down sewage and oil spills (bioremediation) and are used in biogas production by methanogens.

Harmful activities

1. Diseases: humans suffer from cholera (Vibrio cholerae), typhoid (Salmonella typhi), tuberculosis (Mycobacterium tuberculosis), tetanus and pneumonia; plants suffer from citrus canker and bacterial wilt; animals from anthrax.
2. Food spoilage and poisoning: bacteria spoil milk, meat and canned food; Clostridium botulinum produces a deadly toxin (botulism).
3. Loss of soil fertility: denitrifying bacteria (Pseudomonas denitrificans) convert nitrates to nitrogen gas, lowering soil nitrogen.
4. Biological weapons: anthrax bacteria have been misused as bioweapons.

Economic importance of bacteria in agriculture and industry (5 marks)

In agriculture

1. Nitrogen fixation: symbiotic Rhizobium in legume nodules and free-living Azotobacter and cyanobacteria fix atmospheric $\text{N}_2$ into usable ammonia, reducing the need for chemical fertilizer.
2. Nitrification: Nitrosomonas converts ammonia to nitrite and Nitrobacter converts nitrite to nitrate, which plants absorb.
3. Decomposition and humus formation: saprophytic bacteria decay dead plants and animals, return minerals to the soil and improve its fertility.
4. Biological control: Bacillus thuringiensis (Bt) produces a toxin that kills insect pests, a safe biopesticide.
5. Manure and biogas: methanogenic bacteria produce biogas and slurry from cattle dung.

In industry

1. Dairy: Lactobacillus and Streptococcus make curd, cheese, butter and yoghurt.
2. Vinegar and organic acids: Acetobacter oxidises ethanol to acetic acid; other bacteria give lactic and citric acid.
3. Antibiotics and vitamins: Streptomyces gives streptomycin and tetracycline; bacteria produce vitamin $\text{B}_{12}$.
4. Fibre and leather: retting of jute and flax by Clostridium; tanning of leather.
5. Genetic engineering: E. coli is used to make human insulin and growth hormone.

Five beneficial applications of microorganisms in industrial biotechnology (5 marks)

1. Fermented foods and beverages: yeast (Saccharomyces cerevisiae) ferments sugar to ethanol and $\text{CO}_2$ in making beer, wine and bread; Lactobacillus makes curd, cheese and yoghurt.
2. Antibiotics: Penicillium notatum produces penicillin; Streptomyces griseus produces streptomycin. These are produced in large fermenters.
3. Organic acids and enzymes: Aspergillus niger gives citric acid; Acetobacter gives acetic acid (vinegar); Bacillus and Aspergillus give amylase and protease used in detergents, textile and food processing.
4. Recombinant products: genetically modified E. coli and yeast produce human insulin, growth hormone and hepatitis B vaccine.
5. Biofuel and waste treatment: methanogens produce biogas from organic waste; yeast gives bioethanol; microbes treat sewage and clean oil spills (bioremediation).

Other applications include single-cell protein (Spirulina) and vitamin $\text{B}_{12}$ production.

Structure of a typical bacteriophage (T4 phage) (5 marks)

A bacteriophage is a virus that infects bacteria. The T4 phage of E. coli is a tadpole-shaped, tailed particle about 200 nm long with three main parts.

1. Head (capsid): a hexagonal (icosahedral) protein coat made of capsomeres. It encloses a single linear molecule of double-stranded DNA, the genetic material.
2. Collar: a short neck joining head and tail.
3. Tail: a hollow tail tube (core) surrounded by a contractile sheath made of protein. At its end lies a base plate bearing six tail fibres and spikes.

Function of parts:

• Tail fibres attach to specific receptors on the bacterial cell wall.
• The sheath contracts and the core is pushed through the wall, injecting the DNA into the bacterium.
• The empty protein coat stays outside as a "ghost".

        ___
       /   \   <- Head (capsid) containing DNA
       \___/
        | |    <- Collar
        |||    <- Sheath (contractile) around core
        |||
      __|_|__  <- Base plate
      /  |  \  <- Tail fibres and spikes