Acholeplasma

Acholeplasma is a genus of bacteria in the class Mollicutes, order Acholeplasmatales, family Acholeplasmataceae. Members are among the wall-less, small-sized bacteria known as Mollicutes, and they lack a peptidoglycan cell wall, giving them pleomorphic shapes and a fragile membrane. Their membranes typically incorporate sterols, such as cholesterol, which are required for growth and membrane stability.

Most Acholeplasma species are nutritionally fastidious and rely on rich media; they do not form typical Gram-positive or Gram-negative cell wall-structured organisms and are not reliably stained by Gram stain. They can be cultured on specialized media containing serum or lipid supplements (for example, PPLO or SP-4 media) and cholesterol.

Acholeplasma laidlawii is the best-known species and has been widely studied as a model organism in membrane biology and as a contaminant in cell culture and fermentation systems. Other species have been isolated from plants, animals, and insect hosts, and most Acholeplasma are considered nonpathogenic or opportunistic; pathogenic associations are rare and context-dependent.

Genomic and metabolic traits: Acholeplasmas have relatively small genomes and limited biosynthetic capabilities, reflecting their reliance on their hosts or rich media. They lack cell walls, which makes them intrinsically resistant to antibiotics that target cell wall synthesis, such as beta-lactams, and they are typically treated with antibiotics effective against mollicutes, such as tetracyclines or macrolides when pathogenic.

In summary, Acholeplasma comprises wall-less, fastidious bacteria of the Mollicutes class, notable for their small genomes, cholesterol-dependent membranes, and frequent presence as cell culture contaminants or plant/animal associates.