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DgcZ is the main cyclic dimeric GMP (c-di-GMP)-producing diguanylate cyclase (DGC) controlling biosynthesis of the exopolysaccharide poly-β-1,6- N -acetylglucosamine (poly-GlcNAc or PGA), which is essential for surface attachment of Escherichia coli . Although the complex regulation of DgcZ has previously been investigated, its primary role and the physiological conditions under which the protein is active are not fully understood. Transcription of dgcZ is regulated by the two-component system CpxAR activated by the lipoprotein NlpE in response to surface sensing. Here, we show that the negative effect of a cpxR mutation and the positive effect of nlpE overexpression on biofilm formation both depend on DgcZ. Coimmunoprecipitation data suggest several potential interaction partners of DgcZ. Interaction with FrdB, a subunit of the fumarate reductase complex (FRD) involved in anaerobic respiration and in control of flagellum assembly, was further supported by a bacterial-two-hybrid assay. Furthermore, the FRD complex was required for the increase in DgcZ-mediated biofilm formation upon induction of oxidative stress by addition of paraquat. A DgcZ-mVENUS fusion protein was found to localize at one bacterial cell pole in response to alkaline pH and carbon starvation. Based on our data and previous knowledge, an integrative role of DgcZ in regulation of surface attachment is proposed. We speculate that both DgcZ-stimulated PGA biosynthesis and interaction of DgcZ with the FRD complex contribute to impeding bacterial escape from the surface. IMPORTANCE Bacterial cells can grow by clonal expansion to surface-associated biofilms that are ubiquitous in the environment but also constitute a pervasive problem related to bacterial infections. Cyclic dimeric GMP (c-di-GMP) is a widespread bacterial second messenger involved in regulation of motility and biofilm formation, and plays a primary role in bacterial surface attachment. E. coli possesses a plethora of c-di-GMP-producing diguanylate cyclases, including DgcZ. Our study expands the knowledge on the role of DgcZ in regulation of surface attachment and suggests that it interconnects surface sensing and adhesion via multiple routes.

SummaryDiguanylate cyclases synthesize the second messenger c-di-GMP, which in turn governs a plethora of physiological processes in bacteria. Although most diguanylate cyclases harbor sensory domains, their input signals are largely unknown. Here, we demonstrate that diguanylate cyclase DgcZ (YdeH) from Escherichia coli is regulated allosterically by zinc. Crystal structures show that the zinc ion is bound to the 3His/1Cys motif of the regulatory chemoreceptor zinc-binding domain, which mediates subunit contact within the dimeric enzyme. In vitro, zinc reversibly inhibits DgcZ with a subfemtomolar Ki constant. In vivo, bacterial biofilm formation is modulated by externally applied zinc in a DgcZ- and c-di-GMP-dependent fashion. The study outlines the structural principles of this zinc sensor. Zinc binding seems to regulate the activity of the catalytic GGDEF domains by impeding their mobility and thus preventing productive encounter of the two GTP substrates.