Acute Sensitivity of V. cholerae to Phosphate Starvation: A Possible Case of Futile Metabolism.

Abstract

Multi-nutrient starvation profiles are emerging as an essential feature of human pathogen studies. In the present work, we attempted to understand why V. cholerae cannot survive in the growth media that includes carbon and nitrogen but lacks phosphate. However, it can survive starvation in artificial seawater without all three major nutrients (carbon, nitrogen, and phosphate). V. cholerae survival was critically affected below ten mM of phosphate content in the media. Interestingly, the survival of the bacteria in low phosphate conditions improved when cultured under sub-optimal growth conditions, sub-optimal C: N ratio, non-metabolizable nutrient sources, and activation of stringent response. The phosphate starved cells had low ATP levels and high NADH levels; A quick drop in ATP, coupled with impaired redox potential, may lead to cell death. We also observed the acute sensitivity to phosphate limitation among the other members of the genus Vibrio. Among those, V. vulnificus and V. cholerae showed the highest sensitivity (< 0.1%). Among the members of γ-proteobacteria, E. coli and C. sakazaki and S. Typhimurium showed the lowest sensitivity (10%), and the A. hydrophila and V. harvey showing intermediate (1 - 2%) survival in low phosphate condition. The presence of carbon and nitrogen in the media over-weigh the information about the lack of phosphate that would cause continued but futile metabolism. The current study shows a general lack of coordination between carbon, nitrogen, and phosphate metabolism in V. cholerae.