Inactivation of the stress- and starvation-inducible gls24 operon has a pleiotrophic effect on cell morphology, stress sensitivity, and gene expression in Enterococcus faecalis

Enterococcus faecalis induces the synthesis of at least 42 proteins during 24 h of glucose starvation. Because of its induction during carbohydrate an d complete starvation (incubation in tap water) and CdCl2 and bile salts st resses, one of these proteins (Gls24) was qualified as a "general stress pr otein" and was analyzed at the molecular level. Its corresponding gene, gls 24, seems to be the penultimate gene of an operon composed, altogether, of six open reading frames (ORFs). The ORF preceding gls24 (orf4) showed very strong identity with gls24. The deduced polypeptides of these two genes sho wed similarity with a 20-kDa hypothetical protein from Lactococcus lactis a nd an alkaline stress protein from Staphylococcus aureus with no previously known biological significance. Data from the operon sequence and Northern analysis led to the conclusions that (i) gls24 possesses its own promoter w hich is especially induced at the onset of starvation and (ii) the operon p romoter is stress inducible in exponential-phase cells. A mutation in the g ls24 gene led to a severe reduction of growth rate and reduction of surviva l against 0.3% bile salts in the 24-h-starved cells compared to the wild-ty pe strain. Moreover, the chain length of the mutant is significantly reduce d during growth. These results argue strongly for a role of the protein Gls 24 and/or GlsB in morphological changes and in stress tolerance in E. faeca lis. Comparison of two-dimensional protein gels from wild-type cells with t hose from gls24 mutant cells revealed a pleiotropic effect of the mutation on gene expression. At least nine proteins were present in larger amounts i n the mutant. For six of them, the corresponding N-terminal microsequence h as been obtained. Three of these sequences map in genes coding for L-lactat e dehydrogenase, lipoamide dehydrogenase, and pyruvate decarboxylase, all i nvolved in pyruvate metabolism.