Characterization of a stable spheroplast type L‐form of Proteus mirabilis D 52 as cell envelope mutant. I. Isolation, growth characteristics, biochemical activities, and sensitivity to bacteriophages

Abstract

A stable spheroplast type L-form could be isolated by transferring 627 single colonies and 195 agar blocks with several colonies of unstable L-forms of Proteus mirabilis D 52 on agar media without supplements of penicillin. The L-form grows well on complex and synthetic agar media, however, it failed to grow in any of the liquid media which have been proved. With one except,ion (formation of acid from maltose) thel-form shows the same bioche mica1 activities like the parent rod-shaped bacterium. However, the insensitivity for variousphages and the failure of DAP in the envelopes demonstrate that there are profound alterations in the biosynthesis and structure of the murein and of the outer wall layers. The results of these investigations and a n ultrastructural analysis (GUMPERT and TAUBENECK 1975) show that the stable spheroplast type L-form LD 52B of Proteus inirabilis must be considered as a true cell envelope mutant.Among the different bacterial forms with altered cell envelopes the &able L-forms are those showing the most profound alterations. L-forms are protoplasts or spheroplasts which are able to grow and to multiply. Dependent on the presence or absence of cell wall structures and on their ability to revert to normal rod-shaped cells, they can be classified as unstable and stable protoplast type L-forms and unstable and stable spheroplast type L-forms, respectively (MARTIN 1964, TAUBENECK and GUM-PERT 1967). Many investigations were undertaken with Proteus mirabilis to explain especially the nature of the stable L-forms. I n a large number of experiments the production 0f.A and B type colonies as defined by DIENES and the isolation of stable protoplast type L-forms from A colonies have repeatedly been reported (DIENES and WEINBERGER 1951, KANDLER and KANDLER 1959, TAUBENECK 1962, TULASNE et al. 1960). However, it was only shortly mentioned by KANDLER and KANDLER (1956), SHARP and DIENES (1959), and TAUBENECK (1962) that also from B type colonies stable L-forms may be obtained. MARTIN (1964) described such an L-form in more detail. He found the cells to be surrounded by a cell wall structure and named this strains "stable spheroplast L-form".The present study describes experiments concerning isolation, conditions for induction, growth characteristics, biochemical activities, and sensitivity to phages of another stable spheroplast type L-form derived from Proteus mirabilis D 52. Together with an ultrastructural analysis (GUMPERT and TAUBENECK 1975) the results show that this stable spheroplast type L-form must be considered as a true envelope mutant. Whereas the main biochemical activities are the same like that of the rod-shaped parent bacteria, t,here are profound alterations in biosynthesis, structure, and function of the cell envelope.

Morphogenesis of rod-shaped sacculi

“…Electron microscopy showed in some cases that there is no visible cell wall in L‐forms of various bacterial species, including E. coli (Gumpert & Taubeneck, 1983). Biochemical analyses of cell wall constituents in L‐forms have yielded variable results, with numerous reports in which muramic acid, A 2 pm, d ‐glutamate or glucosamine was or was not detected in extracts of L‐forms of various bacteria, usually with little quantification (Gumpert & Taubeneck, 1975, 1976, 1983). Hence, the authors are unaware of any published data that eliminate the possibility of a residual peptidoglycan in an established L‐form.…”