Taxonomy
Domain: Bacteria
Phylum: Tenericutes
Class: Mollicutes
Order: Mycoplasmatales
Family: Mycoplasmataceae
Genus: Mycoplasma
Introduction to Mycoplasmas
Mycoplasmas are the smallest self replicating organisms with the smallest genomes. This is because they employed a technique called degenerative evolution: where they limit their resource usage while maintaining their core features, resulting in only consisting of 500- 1000 genes.
This is fundamental to their parasitic nature, being small enough to bind to a host cell and use it to it’s advantage, like a virus, but still able to reproduce on its own (although with more difficulty, making it harder to research in a medium). They are most similarly related to some clostridia species, and probably evolved from a type of gram positive bacteria.
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Below shows a diagram (Francesca Benedetti. (2020).) of the mechanisms involved in control of immune response in the host cell the mycoplasma adheres to, you can learn more about it here.
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Physiology of Mycoplasmas
A general overview for you to explore deeper:
Mycoplasmas have no cell wall around their cell membranes, this makes them somewhat counterproductive to gram stain because of their unique amount of peptidoglycan.
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They are gram negative on a technicality as they are atypical bacteria in that they have no peptidoglycan, meaning they could never retain safranin or crystal violet. The constituents of the membrane can be found here
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They are low in guanine and by definition, cytosine as well.
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Uniquely, they require sterols which is unlike any other prokaryote. Ureaplasmas (a term for mycoplasmas that live in the urinary tract) require urea, which is also a unique requirement.
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They have surface antigens that include membrane proteins, lipoproteins, glycolipids and lipoglycans that occasionally undergo spontaneous variation to avoid detection from an immune system. Some antibodies can inhibit growth of the cell membrane when attached. Antigens can cross react with human tissues to change their profile.
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Resistance to cell wall antibiotics like beta-lactams. Meaning the ones that are effective against it are specialised in attacking the translation process. (Penicillin, vancomycin and cephalosporins don't work).
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Facultative anaerobes except pneumoniae (strict aerobe).
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They are either parasitic or saprotrophic (eat decomposing organic matter similar to fungi).
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Doubling time can be as long as 16 hours, and they have no other method of reproduction, other than binary fission (non-endospore forming).
Citations
Francesca Benedetti. (2020). Mycoplasmas–Host Interaction: Mechanisms of Inflammation and Association with Cellular Transformation. Available: https://doi.org/10.3390/microorganisms8091351. Last accessed 16/11/2021.