Homologous c-di-GMP-Binding Scr Transcription Factors Orchestrate Biofilm Development in Vibrio parahaemolyticus

Abstract

The marine bacterium and human pathogen Vibrio parahaemolyticus rapidly colonizes surfaces by using swarming motility and forming robust biofilms. Entering one of the two colonization programs, swarming motility or sessility, involves differential regulation of many genes, resulting in a dramatic shift in physiology and behavior. V. parahaemolyticus has evolved complex regulation to control these two processes that have opposing outcomes. One mechanism relies on the balance of the second messenger c-di-GMP, where high c-di-GMP favors biofilm formation. V. parahaemolyticus possesses four homologous regulators, the Scr transcription factors, that belong in a Vibrio-specific family of W[F/L/M][T/S]R motif transcriptional regulators, some members of which have been demonstrated to bind c-di-GMP. In this work, we explore the role of these Scr regulators in biofilm development. We show that each protein binds c-di-GMP, that this binding requires a critical R in the binding motif, and that the biofilm-relevant activities of CpsQ, CpsS, and ScrO but not ScrP are dependent upon second messenger binding. ScrO and CpsQ are the primary drivers of biofilm formation, as biofilms are eliminated when both of these regulators are absent. ScrO is most important for capsule expression. CpsQ is most important for RTX-matrix protein expression, although it contributes to capsule expression when c-di-GMP levels are high. Both regulators contribute to O-antigen ligase expression. ScrP works oppositely in a minor role to repress the ligase gene. CpsS plays a regulatory checkpointing role by negatively modulating expression of these biofilm-pertinent genes under fluctuating c-di-GMP conditions. Our work further elucidates the multifactorial network that contributes to biofilm development in V. parahaemolyticus. IMPORTANCE Vibrio parahaemolyticus can inhabit open ocean, chitinous shells, and the human gut. Such varied habitats and the transitions between them require adaptable regulatory networks controlling energetically expensive behaviors, including swarming motility and biofilm formation, which are promoted by low and high concentrations of the signaling molecule c-di-GMP, respectively. Here, we describe four homologous c-di-GMP-binding Scr transcription factors in V. parahaemolyticus. Members of this family of regulators are present in many vibrios, yet their numbers and the natures of their activities differ across species. Our work highlights the distinctive roles that these transcription factors play in dynamically controlling biofilm formation and architecture in V. parahaemolyticus and serves as a powerful example of regulatory network evolution and diversification.

OpaR Controls the Metabolism of c-di-GMP in Vibrio parahaemolyticus

“…Double gene mutant of scrG and scrC does not swarm but produces a more highly wrinkled colony than those of the single-gene mutants, suggesting that they have cumulative effects on biofilm formation ( Kim and McCarter, 2007 ). ScrO, a newly described GGDEF-type protein, is encoded by the scrMNO operon ( Kimbrough et al, 2020 ). Deleting scrO or the entire operon decreases biofilm formation and alters biofilm architecture and matrix production visualized on Congo red ( Kimbrough et al, 2020 ).…”

A trigger phosphodiesterase modulates the global c-di-GMP pool, motility and biofilm formation inVibrio parahaemolyticus

“…The content of the V. parahaemolyticus genome suggests that this bacterium has an important signaling potential, especially for forming c-di-GMP signaling modules. The few modules that have been explored to this date have a role in controlling biofilm formation and swarming motility (17, 22, 23, 25, 26). In this report we unveiled a new c-di-GMP signaling component involved in the regulation of planktonic motility and surface behaviors, the PDE TpdA.…”

“…C-di-GMP levels positively regulate the expression of the cpsA-K locus through the activation of the c-di-GMP receptors CpsR, CpsQ, and ScrO (15,17). The main drivers of the activation of biofilm matrix production are CpsQ and ScrO (17).…”

“…Biofilm formation in V. parahaemolyticus requires the production of the capsular exopolysaccharide CPSA, made by biosynthetic proteins encoded in the cpsA - K locus (15, 16). C-di-GMP levels positively regulate the expression of the cpsA - K locus through the activation of the c-di-GMP receptors CpsR, CpsQ, and ScrO (15, 17). The main drivers of the activation of biofilm matrix production are CpsQ and ScrO (17).…”

“…C-di-GMP levels positively regulate the expression of the cpsA - K locus through the activation of the c-di-GMP receptors CpsR, CpsQ, and ScrO (15, 17). The main drivers of the activation of biofilm matrix production are CpsQ and ScrO (17). Motility, on the other hand, requires the production of either a polar flagellum in the case of swimming motility, or lateral flagella that are used for swarming over solid surfaces (18–20).…”