The Two Chemotaxis Clusters inCaulobacter crescentusPlay Different Roles in Chemotaxis and Biofilm Regulation
ABSTRACTThe holdfast polysaccharide adhesin is crucial for irreversible cell adhesion and biofilm formation inCaulobacter crescentus. Holdfast production is tightly controlled via developmental regulators, as well as via environmental and physical signals. Here, we identify a novel mode of regulation of holdfast synthesis that involves chemotaxis proteins. We characterized the two identified chemotaxis clusters ofC. crescentusand showed that only the previously characterized major cluster is involved in the chemotactic response toward different carbon sources. However, both chemotaxis clusters encoded in theC. crescentusgenome play a role in biofilm formation and holdfast production by regulating the expression ofhfiA, the gene encoding the holdfast inhibitor HfiA. We show that CheA and CheB proteins act in an antagonistic manner, as follows: while the two CheA proteins negatively regulatehfiAexpression, the CheB proteins are positive regulators, thus providing a modulation of holdfast synthesis and surface attachment.IMPORTANCEChemosensory systems constitute major signal transduction pathways in bacteria. These systems are involved in chemotaxis and other cell responses to environment conditions, such as the production of adhesins to enable irreversible adhesion to a surface and surface colonization. TheC. crescentusgenome encodes two complete chemotaxis clusters. Here, we characterized the second novel chemotaxis-like cluster. While only the major chemotaxis cluster is involved in chemotaxis, both chemotaxis systems modulateC. crescentusadhesion by controlling expression of the holdfast synthesis inhibitor HfiA. Here, we identify a new level in holdfast regulation, providing new insights into the control of adhesin production that leads to the formation of biofilms in response to the environment.