L-form bacteria

L-form bacteria, also known as L-phase bacteria, L-phase variants or cell wall-deficient (CWD) bacteria, are growth forms derived from different bacteria. They lack cell walls. Two types of L-forms are distinguished: unstable L-forms, spheroplasts that are capable of dividing, but can revert to the original morphology, and stable L-forms, L-forms that are unable to revert to the original bacteria. L-form bacteria were first isolated in 1935 by Emmy Klieneberger-Nobel, who named them "L-forms" after the Lister Institute in London where she was working. She first interpreted these growth forms as symbionts related to pleuropneumonia-like organisms (PPLOs, later commonly called mycoplasmas). Mycoplasmas (now in scientific classification called Mollicutes), parasitic or saprotrophic species of bacteria, also lack a cell wall (peptidoglycan/murein is absent). Morphologically, they resemble L-form bacteria. 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. Both, mycoplasmas and L-form bacteria are resistant against penicillin. After the discovery of PPLOs (mycoplasmas/Mollicutes) and L-form bacteria, their mode of reproduction (proliferation) became a major subject of discussion. In 1954, using phase-contrast microscopy, continual observations of live cells have shown that L-form bacteria (previously also called L-phase bacteria) and pleuropneumonia-like organisms (PPLOs, now mycoplasmas/Mollicutes) ) do not proliferate by binary fission, but by a uni- or multi-polar budding mechanism. 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. Additionally, electron microscopic studies have been performed. Bacterial morphology is determined by the cell wall.