Functional Insights Into the Role of in (p)ppGpp Metabolism of .

The stringent response, an adaptive response to nutrient limitation and exposure to xenobiotics in bacteria, is mediated by two intracellular signaling molecules, pppGpp and ppGpp, together called (p)ppGpp. The cellular level of (p)ppGpp in bacterial cells is controlled by the Rel/Spo family of proteins. In the cholera pathogen, , (p)ppGpp metabolism is regulated by the products of at least three genes , , and . In this study, we identify and characterize the function of the guanosine-5'-triphosphate 3'-diphosphate pyrophosphatase A (GppA) encoding gene of . Genomic analysis indicates that the locus is conserved in vibrios and organized as a bicistronic operon along with the gene. We engineered the genome of to develop different mutants devoid of GppA and/or other phosphate metabolic enzymes. Our findings indicate that in , GppA plays an important role in the conversion of pppGpp to ppGpp during amino acid deprivation but not during glucose starvation. Quantitative analyses of the transcript level reveal its differential expression pattern at different growth phases and starvation conditions. It has been observed that the GppA deficiency during amino acid starvation condition could be complemented by overexpressing the exopolyphosphatase coding gene of . By deletion analysis, we further demonstrate that the amino and carboxy terminal sequences flanking the Ppx-GppA motif of the GppA protein of are also important for its enzymatic function.