lform

An L-form, or L-phase form, is a bacterial cell that lacks a rigid peptidoglycan cell wall or has only a reduced one. L-forms can arise from otherwise walled bacteria under certain stress conditions or be maintained as stable wall-deficient variants. The term originates from observations in the 1930s by Emmy Klieneberger-Nobel in studies of Bacillus and other genera.

Physiologically, L-forms have a flexible cytoplasmic membrane and a pleomorphic morphology, ranging from spherical to elongated. Without a wall, they are typically more osmotically fragile and often require osmoprotective environments to survive. They reproduce by unconventional means, such as budding or irregular fission, rather than typical binary fission, and they may revert to their walled form when conditions permit.

L-forms have clinical and research significance. They are of interest because they illustrate alternatives to cell-wall–targeting antibiotics and may contribute to persistence or relapsing infections under antibiotic treatment. In the laboratory, L-forms are studied to understand cell membrane biology, wall biosynthesis, and the limits of cellular life. They are not a taxonomic group but a phenotypic state that can occur in many bacterial species; stability and behavior vary by organism and environmental conditions.

Because L-forms can be easily mistaken for debris or contaminant and because they can be difficult to culture, they pose diagnostic and interpretive challenges in clinical microbiology.