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Microbes (see also microorganism) is a name used to describe a diverse group of organisms, divided into the viruses, unicellular groups (Archaea, Eubacteria, Protista, some fungi, and some Chlorophyta), and a small number of organisms with a simple multicellular structure (the larger fungi and Chlorophyta). These larger microorganisms are characterized by having a filamentous, sheet-like or parenchymatous thallus that does not display true tissue differentiation. Most microbes cannot be seen without the 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 man-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 sole source of carbon and energy Methylotroph
  • Uses reduced methane as 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


Related Terms

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