Prentice, J. A. | bioRxiv Science

bioRxiv2022

Synergy between c-di-GMP and quorum-sensing signaling in Vibrio cholerae biofilm morphogenesis

Transitions between individual and communal lifestyles allow bacteria to adapt to changing environments. Bacteria must integrate information encoded in multiple sensory cues to appropriately undertake these transitions. Here, we investigate how two prevalent sensory inputs converge on biofilm morphogenesis: quorum sensing, which endows bacteria with the ability to communicate and coordinate group behaviors, and second messenger c-di-GMP signaling, which allows bacteria to detect and respond to environmental stimuli. We use Vibrio cholerae as our model system, the autoinducer AI-2 to modulate quorum sensing, and the polyamine norspermidine to modulate NspS-MbaA-mediated c-di-GMP production. Individually, AI-2 and norspermidine drive opposing biofilm phenotypes, with AI-2 repressing and norspermidine inducing biofilm formation. Surprisingly, however, when AI-2 and norspermidine are simultaneously detected, they act synergistically to elevate biofilm formation. We show that this effect is caused by quorum-sensing-mediated activation of nspS-mbaA expression, which increases the levels of NspS and MbaA, and in turn, c-di-GMP biosynthesis, in response to norspermidine. Increased MbaA-synthesized c-di-GMP activates the VpsR transcription factor, driving elevated expression of genes encoding key biofilm matrix components. Thus, in the context of biofilm formation in V. cholerae, quorum-sensing regulation of c-di-GMP-metabolizing receptor levels connects changes in cell population density to detection of environmental stimuli. ImportanceThe development of multicellular communities, known as biofilms, facilitates beneficial functions of gut microbiome bacteria and makes bacterial pathogens recalcitrant to treatment. Understanding how bacteria regulate the biofilm lifecycle is fundamental to biofilm control in industrial processes and in medicine. Here, we demonstrate how two major sensory inputs - quorum-sensing communication and second messenger c-di-GMP signaling - jointly regulate biofilm morphogenesis in the global pathogen Vibrio cholerae. We characterize the mechanism underlying a surprising synergy between quorum-sensing and c-di-GMP signaling in controlling biofilm development. Thus, the work connects changes in cell population density to detection of environmental stimuli in a pathogen of clinical significance.

microbiology↗

bioRxiv2021

Quantitative input-output dynamics of a c-di-GMP signal-transduction cascade in Vibrio cholerae

Bacterial biofilms are multicellular communities that collectively overcome environmental threats and clinical treatments. To regulate the biofilm lifecycle, bacteria commonly transduce sensory information via the second-messenger molecule cyclic diguanylate (c-di-GMP). Using experimental and modeling approaches, we quantitatively capture c-di-GMP signal transmission via the bifunctional polyamine receptor NspS-MbaA, from ligand binding to output, in the pathogen Vibrio cholerae. Upon binding of norspermidine or spermidine, NspS-MbaA synthesizes or degrades c-di-GMP, respectively, which in turn, drives alterations specifically to biofilm gene expression. A longstanding question is how output specificity is achieved via c-di-GMP, a diffusible molecule that regulates dozens of effectors. We show that NspS-MbaA signals locally to specific effectors, sensitizing V. cholerae to polyamines. However, local signaling is not required for specificity, as changes to global cytoplasmic c-di-GMP levels can selectively regulate biofilm genes. This work establishes the input-output dynamics underlying c-di-GMP signaling, which could be useful for developing bacterial manipulation strategies.

microbiology↗