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Microbes (microorganism) is a name used to describe a diverse group of organisms. The most known viruses, unicellular groups (Archaea, Eubacteria, Protista, fungi and Chlorophyta). Besides, a few organisms with a simple multicellular structure (fungi and Chlorophyta). The larger microorganisms are characterised by having a filamentous. It is sheet-like or parenchymatous thallus that does not display true tissue differentiation. Most microbes are invisible unless help of a microscope also known as batting.


  • Viruses
  • Bacteria
  • Fungi

Types of microbial growth

Microbes can convert an enormous range of compounds into biomass – from foodstuffs that humans would consider eating, right the way through to compounds, such as cyanides, that are considered highly toxic. Some human-made chemical compounds are new to the natural environment, so microbes have yet to evolve pathways to deal with them.

Classification of microorganisms according to carbon and energy sources

  • Carbon or energy source description
  • Energy from a chemical Chemotroph
  • Energy from light Phototroph
  • Electrons from an organic compound Organotroph
  • Electrons from an inorganic compound Lithotroph
  • Carbon from carbon dioxide Autotroph
  • Carbon from an organic compound Heterotroph

Other terms used to describe the growth of microorganisms

  • Obtain nitrogen from N2 gas rather than ‘fixed’ nitrogen sources Diazotroph
  • Ability to exist at low nutrient concentrations Oligotroph
  • Uses reduced C1 compounds as a sole source of carbon and energy Methylotroph
  • Uses reduced methane as the sole source of carbon and energy Methanotroph
  • Able to use a mixture of heterotrophic and autotrophic growth mechanisms Mixotroph
  • Only able to grow in the presence of salt Halophile

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