L-form bacteria

[3] Mycoplasmas (now in scientific classification called Mollicutes), parasitic or saprotrophic species of bacteria, also lack a cell wall (peptidoglycan/murein is absent).

Therefore, mycoplasmas formerly were sometimes considered stable L-forms or, because of their small size, even viruses, but phylogenetic analysis has identified them as bacteria that have lost their cell walls in the course of evolution.

Microphotograph series of growing microcultures of different strains of L-form bacteria, PPLOs and, as a control, a Micrococcus species (dividing by binary fission) have been presented.

The L-forms are generated in a culture medium that is the same osmolarity as the bacterial cytosol (an isotonic solution), which prevents cell lysis by osmotic shock.

[1][2] One such point mutation D92E is in an enzyme yqiD/ispA (P54383) involved in the mevalonate pathway of lipid metabolism that increased the frequency of L-form formation 1,000-fold.

[1] The reason for this effect is not known, but it is presumed that the increase is related to this enzyme's role in making a lipid important in peptidoglycan synthesis.

[14][15] The two extreme viewpoints on this question are that L-form bacteria are either laboratory curiosities of no clinical significance or important but unappreciated causes of disease.

[21][22][23] Here, the absence of a cell wall can allow production of large amounts of secreted proteins that would otherwise accumulate in the periplasmic space of bacteria.