Lforms

L-forms are cell wall–deficient variants of bacteria and, in rare cases, archaea that can grow and divide without peptidoglycan in their envelopes, provided they are in osmotically stabilized environments. They are pleomorphic and can exhibit a range of shapes rather than a single identifiable form.

L-forms can arise under stress or be induced in the laboratory. They are often produced by exposure to antibiotics that inhibit cell wall synthesis, such as β-lactams, which can trigger the transition from a walled to a wall-deficient state. They can also appear spontaneously in some cultures or as a response to environmental stress. In the lab, L-forms are typically maintained in osmoprotective media to prevent lysis and may revert to walled forms when favorable conditions return.

Morphology and growth of L-forms differ markedly from their walled relatives. Without a rigid cell wall, they lack a defined shape and divide by irregular processes such as budding or extrusion, rather than by typical binary fission. Their cell envelopes are often composed of a lipoprotein and lipid bilayer, and they may exhibit altered membrane properties and metabolic pathways. Because they lack peptidoglycan, L-forms show distinct sensitivities to certain antibiotics and environmental stresses.

Clinical and research relevance remains a topic of discussion. L-forms have been implicated in persistent and recurrent infections and are considered a potential mechanism for antibiotic tolerance. They also provide a model for studying basic aspects of cell growth, division, and cell wall synthesis, contributing to understanding bacterial evolution and resilience. The concept originated in the work of Emmy Klieneberger-Nobel in the 1930s, who described cell wall–deficient variants in culture.