Rank: Species
Lineage: Bacteria;Tenericutes;Mollicutes;Mycoplasmatales;Mycoplasmataceae;Mycoplasma;Mycoplasma pneumoniae
Description: Mycoplasma. This genus currently comprises more than 120 obligate parasitic species found in a wide spectrum of hosts, including humans, animals, insects and plants. The primary habitats of human and animal mycoplasmas are mucous membranes of the respiratory and urogenital tracts, eyes, mammary glands and the joints. Infection that proceeds through attachment of the bacteria to the host cell via specialized surface proteins, adhesins, and subsequent invasion, results in prolonged intracellular persistence that may cause lethality. Once detected in association with their eukaryotic host tissue, most mycoplasmas can be cultivated in the absence of a host if their extremely fastidious growth requirements are met. All mycoplasmas are phenotypically distinguished from other bacteria by their small size (0.3-0.8 micron in diameter) and lack of a cell wall. The latter is one of the major traits that puts them in the separate taxonomic group of microorganisms, class Mollicutes (Latin mollis, soft; cutis, skin). The cell membrane is rich in protein components (up to two thirds of the membrane mass) that to a great extent consists of highly structurally adaptive lipoproteins employed in invading the host immune system, attachment to the host cells, and pathogenic invasion. Most mycoplasmas are non-motile, with the exception of a few flask-shaped human and animal pathogens (M. pneumoniae, M. genitalium, M. gallisepticum, M. pulmonis and M. mobile). Motile mycoplasmas glide over the surface by an unknown mechanism that is suspected to employ actin-like cytoskeletal components as well as motility proteins unique for this microbial group. Cell division proceeds via normal binary fission or via elongation of a parental cell to form multinucleated filaments and the subsequent breakup to form coccoid bodies.Mycoplasmas carry the smallest genomes of self-replicating cells (less than 500 recognizable coding regions), which is one of the reasons they were among the first microorganisms selected for the genome-sequencing projects. The complete sequence of the genome of M. genitalium was the second to be reported following the report on the complete sequence of the Haemophilus influenzae genome. Examination of the mycoplasma genomic data indicates the biochemical pathways where gene reductions took place, and helps define the minimal set of genes essential for a self-replicating cell. During their evolution, mycoplasmas appear to have lost all of the genes involved in amino acid and cofactor biosynthesis, synthesis of the cell wall and lipid metabolism, resulting in a requirement for the full spectrum of substrates and cofactors taken up from the host or from the complex artificial culture medium. They have lost a number of genes involved in cellular processes, such as cell division, heat shock response, regulatory genes, the two-component signal transduction systems, histidine protein kinases or their target response regulators, and most transcription factors. The majority of mycoplasmas are deficient in genes coding for components of intermediary and energy metabolism and thus are dependent mostly on glycolysis as an ATP-generating pathway.
Reference Material:
https://www.ncbi.nlm.nih.gov/genome/?term=Mycoplasma%20pneumoniae
