Ritu's Biology Hub

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.

1. 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

2. 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)

3. 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

4. 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

5. 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

1. 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

2. 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

3. Spirochetes

• They have a twisted or spiral body
• Usually flagellated at one or both ends and hence, motile

4. Pleomorphic (Variable shape)

• Oval to pear shaped Hyphomicrobium produce a bud at the ends of hypha
• Gallionella produce stalks
• Other examples – Corynebacterium, Rhizobium

Continued to Part 2