Structure of Bacterial L Forms and Their Parent Bacteria

Abstract

Light and electron microscopic studies were done on normal cells and L forms of Proteus mirabilis, Staphylococcus aureus, and Corynebacterium sp. grown in liquid media. Under the prevailing growth conditions, the L forms studied were morphologically indistinguishable from one another. They appeared as approximately spherical elements occurring singly or more often connected with each other by thinner portions of cell material. In sections of large L forms, the following structures were seen: a peripheral, triple-layered ("unit") membrane, a granular cytoplasm, nuclear regions, and vacuoles limited by membranes. Small bodies often were present inside the vacuoles. These bodies also contained a peripheral membrane and a granular cytoplasm but usually no nuclear regions. The normal bacteria from which the L forms were derived differed markedly in structure from one another, especially in the surface layers of the cells. Studies on the structure of bacteria have been greatly facilitated during the past 10 years thanks to increased resolution of the available electron microscopes and to advances in electron-microscopical techniques, e.g., the fixation and embedding methods developed by Kellenberger, Ryter, and Sechaud (1958). However, relatively few detailed reports on the structure of bacterial L forms have appeared so far (

Demonstration of the Phenomena of Microbial Persistence and Reversion with Bacterial L-Forms in Human Embryonic Kidney Cells

“…Viability of these persisting forms was attested to by the sporadic reversions to classical S. faecalis bacteria that occurred in M-1infected cell systems after various latent periods. In addition, the large size range of particles (0.05 to 0.7 Am) occurring within vesicles of mature L-forms growing in pure culture is consistent with Weibull's speculation that smaller L-bodies inside or connected with larger L-forms may grow and divide (19). It might therefore be speculated that dense bodies can grow into immature, undifferentiated L-forms capable of reproduction only within a protected environment such as that found within the vesicle of the mature L-form, or perhaps within HEK cells.…”

Morphology and Ultrastructure of Staphylococcal L Colonies: Light, Scanning, and Transmission Electron Microscopy

“…Small, spherical, densely packed cells without apparent nuclear material, which have been previously defined as elementary corpuscles (2), were observed, but morphological evidence of their derivation from the larger forms could not be appreciated. Small cells within large cells, as previously described (1,10,15) in broth cultures of L-phase variants, likewise were not observed.…”

Chemical, Biological, and Structural Properties of StableProteusL Forms and Their Parent Bacteria

“…3) had the appearance of triple-layered "unit membranes" (31). Walls of gram-negative bacteria have often been characterized as "unit membranes," but recent electron microscopic studies have revealed a more complex structure of such walls when they are sectioned in situ (7,12,21,40). The present study thus shows that subcellular structures may have different appearances in the intact cell and after isolation.…”