Microbial Diversity and Roles in Ecosystems

Posted on Mar 27, 2025 in Biology

F.1.8 Virus Structure and Diversity

A virus is a non-cellular agent consisting of a protein coat (capsid) and genetic material.

  • The genetic material may be DNA (adenovirus) or RNA (retrovirus) and may be single-stranded or double-stranded.
  • For some viruses, the protein coat may be exposed (naked capsid), while others may be covered in a membranous bilayer (enveloped capsid).
  • Retroviruses have a reverse transcriptase component to allow for the production of viral DNA.

F.1.9 Microscopic Eukaryote Diversity

Examples include Saccharomyces, Amoeba, Plasmodium, Paramecium, Euglena, and Chlorella.

  • Amoeba – single-celled organism that inhabits freshwater ponds and moves and captures food via cell extensions called pseudopodia.
  • Plasmodium – a genus of parasitic protozoa that causes malaria as part of a complex life cycle involving two hosts (humans and mosquitoes).
  • Paramecium – a protozoan that inhabits freshwater environments and moves via the coordinated beating of tiny cilia.
  • Saccharomyces – a genus of single-celled fungus known as yeasts and employed extensively in the fermentation process.
  • Chlorella – a genus of unicellular green algae that possesses a singular cup-shaped chloroplast within its cytoplasm.
  • Euglena – a flagellated protozoan that contains chloroplasts and is commonly present in pond water.

F.2.1 Roles of Microbes in Ecosystems

Microbes play crucial roles as producers, nitrogen fixers, and decomposers.

Producers

Change inorganic molecules into organic molecules that can be used as food by all other organisms in the environment.

Nitrogen Fixers

Remove nitrogen from the atmosphere and convert it into nitrates, which can be used by the producers.

Decomposers

Break down organic material, then release inorganic components from the organic matter into the environment.

F.2.3 Roles in the Nitrogen Cycle

Key players include Rhizobium, Azotobacter, Nitrosomonas, Nitrobacter, and Pseudomonas denitrificans.

Nitrogen Fixation

  • Rhizobium is found in the root nodules of certain leguminous plants and fixes nitrogen gas into ammonia for its host (mutualistic nitrogen fixation).
  • Azotobacter is found living freely in the soil and also fixes nitrogen, but without the need of a host (free-living nitrogen fixation).

Nitrification

  • Nitrosomonas is able to convert ammonium (NH4+) into nitrites (NO2–).
  • Nitrobacter is able to convert the nitrites (NO2–) into nitrates (NO3–), which can then be absorbed by plant roots via active transport.

Denitrification

  • Pseudomonas denitrificans is able to convert nitrites (NO2–) and nitrates (NO3–) into nitrogen gas (N2), which can return to the atmosphere.

F.2.4 Conditions Favoring Denitrification and Nitrification

Nitrification is the biological oxidation of ammonia to produce nitrate ions (via the intermediate production of nitrites).

Denitrification is the biological process of nitrate reduction to produce molecular nitrogen (N2).