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
  1. 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)
  1. 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
  1. 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
  1. 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
  1. 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
  1. Spirochetes
  • They have a twisted or spiral body
  • Usually flagellated at one or both ends and hence, motile
  1. 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

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