Characterization of the gluconate utilization system of Vibrio cholerae with special reference to virulence modulation

Abstract

Orthologs search identified that the Vibrio cholerae gluconate (Gnt) utilization system minimally consisted of the Entner–Doudoroff (ED) pathway (edd and eda) and three other genes, namely gntU, gntK and gntR. This system appeared unique by genomic organization of component genes into two operons transcribed in opposite directions. In silico analysis indicated GntU as an inner-membrane protein functioning for transport and GntK as a kinase with cytosolic localization that generates Gnt6P, which is then metabolized through the ED pathway. Enzyme 6-phosphogluconate dehydratase encoded by edd converts Gnt6P to 2-keto-3-deoxy-6-phosphogluconate (KDPG), which is metabolized by the action of KDPG-aldolase encoded by eda. Transcriptional upregulation of the Gnt utilization genes in the gntR mutant matched well to a predicted repressor role of GntR. GntR displayed DNA binding to a region in the promoters of two bi-directionally transcribed operons. Growth defect of mutants in Gnt-supplemented media confirmed obligate involvement of these genes in Gnt utilization and such defect was restored upon complementation. Defective Gnt utilization resulted in attenuation of colonization potential and reduction of cholera toxin secretion in V. cholerae. The ED pathway mutants showed the highest level of virulence attenuation. Overall, this study established a minimal requirement of the V. cholerae Gnt utilization system, which played a critical role in pathogenesis.