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 exception (formation of acid from maltose) the L‐form shows the same biochemical activities like the parent rod‐shaped bacterium. However, the insensitivity for various phages 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 an ultrastructural analysis (GUMPERT and TAUBENECK 1975) show that the stable spheroplast type L‐form LD 52B of Proteus mirabilis must be considered as a true cell envelope mutant.