|MadSci Network: Microbiology|
Aphragamabacteria are "wall-less" bacteria (a= without, not, phragma = wall) known as MYCOPLASMAS. They are known to cause some unpleasant diseases (both sexually transmitted and a mild "walking" pneumonia). Most bacteria need walls to keep their innards from swelling, and their fragile membrane from bursting (from the osmotic inflow of water) but the mycoplasmas have a special, high-strength membrane.
Because mycoplasmas lack a wall, they can be found in strange shapes (branched globs, spiral filaments, etc) and can even squeeze through special filters used to remove bacteria from water. In the case of scientist growing cells in testubes filled with filter-sterilized broth, the mycoplasmas can be a real pain -- they infect the cell cultures, and can be difficult to get rid of. Because they lack a wall, penicillin, and other antibiotics that kill bacteria by weakening their wall, don't work against mycoplasmas.
Mycoplasmas were thought to be really strange, the smallest of all cells, but their DNA codes turn out to be quite similar to some common, ordinary bacteria (including Bacillus, a gram positive rod-shaped type) with which they probably share a common ancestor. The entire DNA sequence of one species was recently found to contain the smallest number of genes of any cell ( 470 in Mycoplasma genitalium), compared to two or three thousand in typical bacteria like E. coli. Humans, by the way, have roughly 100,000 genes.
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