Bile Acids and Bicarbonate Inversely Regulate Intracellular Cyclic di-GMP in Vibrio cholerae

Abstract

Vibrio cholerae is a Gram-negative bacterium that persists in aquatic reservoirs and causes the diarrheal disease cholera upon entry into a human host. V. cholerae employs the second messenger molecule 3=,5=-cyclic diguanylic acid (c-di-GMP) to transition between these two distinct lifestyles. c-di-GMP is synthesized by diguanylate cyclase (DGC) enzymes and hydrolyzed by phosphodiesterase (PDE) enzymes. Bacteria typically encode many different DGCs and PDEs within their genomes. Presumably, each enzyme senses and responds to cognate environmental cues by alteration of enzymatic activity. c-di-GMP represses the expression of virulence factors in V. cholerae, and it is predicted that the intracellular concentration of c-di-GMP is low during infection. Contrary to this model, we found that bile acids, a prevalent constituent of the human proximal small intestine, increase intracellular c-di-GMP in V. cholerae. We identified four c-di-GMP turnover enzymes that contribute to increased intracellular c-di-GMP in the presence of bile acids, and deletion of these enzymes eliminates the bile induction of c-di-GMP and biofilm formation. Furthermore, this bile-mediated increase in c-di-GMP is quenched by bicarbonate, the intestinal pH buffer secreted by intestinal epithelial cells. Our results lead us to propose that V. cholerae senses distinct microenvironments within the small intestine using bile and bicarbonate as chemical cues and responds by modulating the intracellular concentration of c-di-GMP.

AcsA–AcsB: The core of the cellulose synthase complex from Gluconacetobacter hansenii ATCC23769

“…These values are consistent with physiological concentrations of 1-2 mM for UDP-glucose [39]. The K d value determined here for cyclic-di-GMP is in the micromolar region and lower, consistent with the value of 1.0 M, determined for R. sphaeroides BcsA-BcsB [31], also consistent with physiological concentrations of 0.2-2.5 M for cyclic-di-GMP [40] in Gram-negative bacteria. Interestingly, an earlier report shows cyclic-di-GMP involved in an allosteric interaction [41].…”

Microbial Surface Colonization and Biofilm Development in Marine Environments

“…Surface-associated bacteria usually harbor more c-di-GMP regulators than free-living bacteria, presumably as an adaptive strategy (120). O 2 , H 2 O 2 , NO, redox potential, light, sucrose, amino acids, polyamines (such as norspermidine and spermidine), Zn 2ϩ , bile acids, bicarbonate, indole, QS autoinducers, cis-2-dodecenoic acid and cis-11-methyl-dodecenoic acid (unsaturated fatty acids that serve as bacterial diffusible signal factors), and nutritional conditions that cause starvation (or depletion of a specific carbon source such as glucose or glycerol) have been identified as environmental cues that induce the bacterial response via altering the intracellular c-di-GMP concentration (480,(492)(493)(494)(495)(496)(497)(498)(499)(500)(501)(502)(503)(504)(505)(506)(507)(508). However, the vast majority of the environmental signals that modulate the activity of the DGCs and PDEs remain unidentified.…”

Living in the matrix: assembly and control of Vibrio cholerae biofilms

“…In addition, some DGCs and PDEs seem to be regulated by the QS pathway independently of HapR, through LuxO and Qrr1-4 85 . Environmental signals, such as polyamines and bile components, have also been shown to modulate abundance and activity of c-di-GMP signaling enzymes 52,62,86,87 .…”