Microbiology (Greek: mikros – small, bios – life bearing, logy – study) is a branch of biology that deals with living organisms of microscopic size: bacteria, fungi, algae, protozoa and viruses. Microbes live in terrestrial, aquatic and atmospheric habitats or in living hosts; some survive hot springs, ice sheets, salty water bodies and arid places. Some are used to prepare curd, bread, cheese, alcohol, vaccines and vitamins; others cause diseases in plants, animals and human beings.
1. Microbes and Their Types
Microbes differ in size, morphology, habitat and metabolism. Types: bacteria, viruses, fungi, microscopic algae and protists.
| Nature | Example |
|---|---|
| Unicellular | Bacteria |
| Multicellular | Fungi |
| Acellular (not composed of cells) | Virus |
2. Bacteria
- Microscopic, single celled prokaryotic organisms without nucleus and other cell organelles; size less than 1 to 10 μm long and 0.2 to 1 μm wide.
- Motile or non-motile; flagella (lash-like appendages) are used for motility.
- Shapes: spherical – cocci (coccus); rod shaped – bacilli (bacillus); spiral – spirilla (spirillum).
- The cell membrane is covered by a strong rigid cell wall; some bacteria have a slimy protective capsule of polysaccharides outside it.
- The cytoplasm holds the nucleoid (incipient nucleus), DNA and ribosomes (site of protein synthesis); there are no membrane bound organelles. Plasmid – a small extra chromosomal circular DNA.