Molecular characterization of vibrio cholerae DeltarelA DeltaspoT double mutants

In Escherichia coli cellular levels of pppGpp and ppGpp, collectively called (p)ppGpp, are maintained by the products of two genes, relA and spoT. Like E. coli, Vibrio cholerae also possesses relA and spoT genes. Here we show that similar to E. coli, V. cholerae DeltarelA cells can accumulate (p)ppGpp upon carbon starvation but not under amino acid starved condition. Although like in E. coli, the spoT gene function was found to be essential in V. cholerae relA (+ )background, but unlike E. coli, several V. cholerae DeltarelA DeltaspoT mutants constructed in this study accumulated (p)ppGpp under glucose starvation. The results suggest a cryptic source of (p)ppGpp synthesis in V. cholerae, which is induced upon glucose starvation. Again, unlike E. coli DeltarelA DeltaspoT mutant (ppGpp(0) strain), the V. cholerae DeltarelA DeltaspoT mutants showed certain unusual phenotypes, which are (a) resistance towards 3-amino-1,2,4-triazole (AT); (b) growth in nutrient poor M9 minimal medium; (c) ability to stringently regulate cellular rRNA accumulation under glucose starvation and (d) initial growth defect in nutrient rich medium. Since these phenotypes of DeltarelA DeltaspoT mutants could be reverted back to DeltarelA phenotypes by providing SpoT in trans, it appears that the spoT gene function is crucial in V. cholerae.