Characteristics of Taxonomic Groups with Soil-inhabiting Forms

Kingdom Monera

The most numerous and widespread organisms on earth. They are prokaryotic and lack a nucleus or other membrane-bounded organelles. The cell wall, outside the plasma membrane, is partially composed of peptidoglycan, a complex structural molecule not found in eukaryotic cells.

Archaebacteria

The most ancient of all organisms.  Three groups:

Eubacteria

Separated by reaction to Gram Stain:

  • Gram negative Eubacteria

    Most eubacteria (about 75%) are gram negative. They include the gliding bacteria, the spirochetes, the vibrios and spiral bacteria, rods, cocci, rickettsias, chlamydias and the photosynthetic cyanobacteria.

     

  • Gram positive Eubacteria

    Include rods, cocci, and the actinomycetes.

    Actinomycetes

    A diverse group of bacteria with filamentous growth.  Classified by mycelium pattern and substrate.  Streptomyces is a well-known example.  Include gram negative and gram positive forms.

    Actinomycetes are abundant in soils that are rich in organic matter and are the source of the characteristic smell of organic soils.

    Actinomycete mycelium

    Coiled actinomycete-like bacterial cells

  • Mycoplasmas

  • Smallest known cells with minimum DNA needed to code for a functioning cell. They lack cell walls and most exist as intracellular parasites of plants or animals. 
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    References

    Dindal, D. 1990. Soil Biology Guide. John Wiley and Sons, NY.

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