Cell wall turnover in lyt mutants of Bacillus subtilis

One of the reported phenotypes of Bacillus subtilis strains containing the lyt mutations is a deficiency in cell wall turnover. However, it has recently been shown in our laboratory that these mutant cells can turn over their walls under certain conditions (Vitkovic et al. [2, 11] and Abstr. K3, Annu. Meet. Am. Soc. Microbiol., 1984, p. 147). I show in this paper that the long lag in wall turnover of lyt-1 (FJ3) and lyt-2 (FJ6) strains coincided with the time it took cells (which grow in long chains) to reach the end of exponential growth and to begin separating. At this time, the specific activity of N-acetylmuramyl-L-alanine amidase in the mutant strains reached the same level as in the standard strain in mid-exponential growth phase. Wall turnover was therefore probably caused by increased amidase activity. The turnover in strain lyt-15 (Nil5) was initiated by addition of NaCl and its rate reached that of the standard strain at 0.2 M NaCl. The amidase activities isolated from the lyt-15 and the standard strains varied similarly with NaCl concentration. When walls were probed with amidases and lysozyme in the presence of increasing concentrations of NaCl, the lyt-15 cell wall appeared to be very different from the walls of the standard strain or M. luteus (a standard lysozyme substrate). The results suggest that turnover deficiency in the lyt-15 strain may be due to a change in its wall resulting in a reversible resistance to turnover.