Virus, Bacteria, BGA and Mycoplasma: Quick Study Material

Virus, Bacteria, BGA and Mycoplasma: Quick Study Material

Virus, Bacteria, Blue Green Algae and Mycoplasma: Full study material in summerized form


⚫ Study of virus: Virology

⚫ Father of virology: Stanley

⚫ Term virus was coined by Louis Pasteur.

⚫ Link between living and non living.

⚫ Contain either DNA or RNA.

⚫ No metabolism.

⚫ Host specificity.

⚫ Obligate parasite.

⚫ Living character of virus is the presence of nucleic acid (DNA/RNA) and its non living property is that it can be crystallized. So virus is also called as Biological puzzle.

⚫ Virus is a living particle.

⚫ Virions: The fully assembled mature particle of virus capable of causing infection. It contains both protein and nucleic acid.

⚫ Viriods: Smallest infectious agent contains only nucleic acid(RNA) without protein coat.

⚫ Virusoids: Fragment of RNA. Normally non-infectious.

⚫ Prions: Infectious agents which contain only protein.

⚫ Plant virus: Usually RNA virus but Cauliflower Mosaic Virus posses DNA.

⚫ Animal virus: Usually DNA virus but Retrovirus, reo virus posses RNA.

⚫ Viral disease can be diagnosed by antigen-antibody reactions.

⚫ Apical meristem- Virus free plant part- Used in tissue culture to produce virus free plant.

⚫ Diseases caused by virus:
-Tobacco mosaic disease
-Leaf curl of papaya
-Grassy shoot of papaya
-Bunchy top of banana
-Tomato leaf culr
-Mosaic of sugarcane
-Tungro disease of rice


⚫ Study of bacteria - Bacteriology

⚫ Term bacteria was coined by Ehrwenberg.

⚫ Father of bacteriology is Robert Koch.

⚫ Father of microbiology is Louis Pasteur.

⚫ Single, circular DNA(ds) Molecule without histone protein is present, called Nucleoid or Incipient nucleus.

⚫ Ribosome: 70s type (50s+30s).

⚫ Smallest bacterium is Dialister pneumosintes and longest bacteria are spirillium.

⚫ Insulin is the first hormones which obtained from genetically engineered bacteria E. coli.

Types of Bacteria

On the basis of shape:

✒ Bacillus : rod shaped. eg. Streptobacillus.
✒ Coccus : Spherical. eg. 
✒ Vibrio : Comma shaped. eg. Vibrio cholera
✒ Spirillum : Spiral shaped eg. 
✒ Pleomorphic : No fixed shape. eg. 

On the basis of flagellation:

✒ Atrichous: flagella absent Eg. Shigella, Lactobacillus, Pasteurella.
✒ Monotrichous: Only one flagellum attached at one pole of organism. Eg. Vibrio cholera
✒ Amphitrichous: 2 flagella one on each end. Eg. Nitrosomonas.
✒ Cephalotrichous: Tuft of flagella attached only at one end. Eg. Helicobacter pylori, Spirochaeta, Treponema pallidum
✒ Lophotrichous: Tuft of flagella attached to both end. Eg. Azotobacter, Pseudomonas.
✒ Peritrichous: Flagella distributed all over the surface of the cell. Eg. Escherichia coli, Salmonella typhi, Clostridium.

Bacteria and their flagella, Modification of bacteria according to their flagella. Bacteria types

On the basis of their functions

✒ Nitrogen fixing bacteria: Convert atmospheric nitrogen to biologically acceptable form in soil.
✒ Free living: Azotobacter, Clostridium, Rhodospirillium 
✒ Symbiotic: Rhizobium
✒ Ammonifying bacteria: Bacillus vulgaris
✒ Nitrifying bacteria (oxidizes NH3 to NO3): Nitrosomonas, Nitrobacter, etc.
✒ Denitrifying bacteria: Convert nitrate to atmospheric N2 gas. Eg. Pseudomonas denitrificans.

On the basis of gram staining:

On the basis of gram staining, Bacteria are of two types. They are "Gram +ve" and "Gram -ve".

Gram +ve

Gram -ve

1. They attain purple/violet color in Gram stain. 1. They attain red/pink color in Gram stain.
2. Thick peptidoglycan cell wall. 2. Thin peptidoglycan cell wall but more complex.
3. More easily treatable with antibiotics. 3. Harder to treat with antibiotics.
4. Mostly coccus and non-capsulated. 4. Mostly bacillus and capsulated.
5. Flagellation is less common. 5. Flagellation is common
6. Mesosome is present. 6. Mesosome is absent.
7. Exotoxin is present. 7. Only endotoxin is present.

Reproduction in bacteria:

Vegetative reproduction

a. Binary fission
b. Budding
c. Fragmentation

Asexual reproduction

a. Endospore formation
b. Conidia formation
c. Zoospores

Sexual reproduction 

a. Transformation
b. Transduction
c. Conjugation

Bacteria as a source of Antibiotics

✒ Neomycin = Streptomyces fradiae
✒ Terramycin = Streptomyces ramosus
✒ Chloramphenicol = Streptomyces venezuelae
✒ Streptomyoin = Streptomyces griseus

Plant diseases

✒ Citrus canker = Xanthomonas citri
✒ Crown gall diseases = Agrobacterium tumefaciens
✒ Fire blight of apple and pear = Erwitia amylovora
✒ Potato wilt = Pseudomonas solanacearum
✒ Ear rot of wheat = Corneybacterium tritici


⚫ Also called as PPLO(Pleuro Pneumonia Like Organism).
⚫ Smallest living cell.
⚫ Simplest, non motile, free-living highly pleomorphic, lack cell wall.
⚫ Highly pleomorphic and can change their shape. Hence, called "Jokers of plant kingdom".
⚫ Sensitive to tetracycline and resistance to penicillin.
⚫ Disease caused by Mycoplasma 
-Little leaf of Brinjal.
-Bunchy top of papaya


⚫ They are also called blue green algae (BGA).
⚫ Oxygen producing prokaryotic organism.
⚫ Connecting link between bacteria and algae.
⚫ They have photoautotrophic and symbiotic mode of nutrition.
⚫ Photosynthetic pigments are phycoerythrin, phycocyanin, chlorophyll-a, carotene, xanthophylls
⚫ Economic importance:-
- Spirulina is used as single cell protein.
- Nostoc, anabaena, scytonema help in nitrogen fixation.
- Water bloom is due to extensive growth of BGA.
- Red colour of red sea is due to Trichodesmium Erythrium.

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