What Are Microorganisms?
They are tiny organisms that can be visualised only under microscope. Microorganisms encompass bacteria, archaea, viruses, protists and fungi. Microorganisms could be prokaryotic or eukaryotic. Prokaryotes lack a true nucleus and membrane-bound organalles whereas the eukaryotic cells are quite the opposite with a membrane limited nucleus and other cell organalles.
- Bacteria –
- Prokaryotic, single-celled with peptidoglycan cell wall
- Abundant in soil, water and as well as in mouth, skin and intestine of higher animals
- Some live in optimal environment whereas some live in extreme temperatures, pH, pressure or salinity
- Beneficial (nutrient cycling, fermentation, photosynthesis) or harmful (diseases)
- 2 bacteria that are visible to the naked eye – Epulopiscium fischelsoni, Thiomargarita namibiensis
- Archaea –
- Prokaryotic, single-celled. Just like bacteria but differ notably in rRNA sequences
- Lack peptidoglycan cell wall
- Differ from bacteria in membrane lipid composition
- Most live in extreme environments
- Only prokaryotes involved in methanogenesis (generation of methane)
- Viruses –
- Acellular organisms that are obligate parasites ie., cannot replicate outside a host cell
- 10,000 times smaller than bacteria
- Usually pathogenic causing various plant and animal diseases
- Protists –
- Eukaryotic, single-celled that include algae, protozoa, slime molds and water molds
- Algae are photosynthetic that along with cyanobacteria produce oxygen
- Protists are unicellular, motile, free-living and principle hunter and grazers. They are also the primary producers of the food chain apart from trees and plants
- Slime molds resemble protozoa in one phase of their life cycle and fungi in another. In the protozoan phase, they hunt for food and engulf them
- Water molds inhabit moist soil or freshwater surface and feed on decaying vegetation
- Fungi –
- They range from unicellular yeasts to multicellular molds and mushrooms
- The multicellular forms have thin, thread-like structures called hyphae that help absorb nutrients from the environment
- Play many beneficial roles like bread making, antibiotic production and mineral nutrient recycling
- Some are pathogenic
Classification Of Microorganisms Based On Shapes
- Cocci (Spherical cells)
- Diplococci – The cells divide and remain together to form pairs
- Long chains – The cells divide and remain together to form chains
- Staphylococcus – divides in random planes to form grape – like clusters
- Micrococcus – divides in 2 planes to form square groups of four cells called tetrads
- Sacrcina – divides in 3 planes to give cubical packets of eight cells
- Bacilli (Rod shaped cells)
- Most bacilli form long chains of rod like cells
- Coccobacilli – short and wide
- Ends of these cells could be flat, rounded, cigarette-shaped or bifurcated
- Vibrio – comma-shaped rods
- Spirochetes
- They have a twisted or spiral body
- Usually flagellated at one or both ends and hence, motile
- Pleomorphic (Variable shape)
- Oval to pear shaped Hyphomicrobium produce a bud at the ends of hypha
- Gallionella produce stalks
- Other examples – Corynebacterium, Rhizobium