PHYSIOLOGICAL AND GENETIC-CHARACTERIZATION OF THE OSMOTIC-STRESS RESPONSE IN BACILLUS-SUBTILIS

Bacillus subtilis cultures submitted to an osmotic upshock (1.5 M NaCl ) lysed unless stationary phase had been reached. Several physiologica l variations were observed, such as delayed growth (adaptation), a fil amentous bacterial appearance, RecA-dependent osmoresistance (SOS), an d cross-induction by a previous stress (heat shock). Osmoresistance an d sporulation seem to share pathways of regulation such as inhibition in the presence of glucose and glutamine and derepression in a catabol ite-resistant mutant such as degUh. However, spores were not obtained on hypertonic media. Mutants of later sporulation stages (spoII, spoII I) presented a response similar to that of the wild-type parent, indic ating that both processes probably shared early controls. Null mutatio ns in any of the known key modulators of sporulation (spoOA or degU) r esulted in similar levels of osmosensitivity. Sensor mutations in kinA and degS also led to strains with altered responses, the kinA mutant being even more osmosensitive than the degS mutant. Several spoOA muta nt phenotypes are due to this gene's control of abrB, a regulator of s tationary-phase events, and an abr B mutation relieved the osmosensiti vity of the spoOd-containing mutant but had no effect on a wild-type s train.