BarA-UvrY Two-Component Regulatory System Represses Biofilms via CsrB.

The formation of biofilms by () and requires the genes, which direct production of a polysaccharide extracellular matrix (Hms-ECM). Despite possessing identical sequences, produces much less Hms-ECM than . The regulatory influences that control Hms-ECM production and biofilm formation are not fully understood. In this study, negative regulators of biofilm production in were identified. Inactivation of the BarA/UvrY two-component system or the CsrB regulatory RNA increased binding of Congo Red dye, which correlates with extracellular polysaccharide production. These mutants also produced biofilms that were substantially more cohesive than the wild type strain. Disruption of was not sufficient for to cause proventricular blockage during infection of fleas. However, this strain was less acutely toxic toward fleas than wild type . Flow cytometry measurements of lectin binding indicated that BarA/UvrY/CsrB mutants may produce higher levels of other carbohydrates in addition to poly-GlcNAc Hms-ECM. In an effort to characterize the relevant downstream targets of the BarA/UvrY system, we conducted a proteomic analysis to identify proteins with lower abundance in the ::Tn5 mutant strain. Urease subunit proteins were less abundant and urease enzymatic activity was lower, which likely reduced toxicity toward fleas. Loss of CsrB impacted expression of several potential regulatory proteins that may influence biofilms, including the RcsB regulator. Overexpression of CsrB did not alter the Congo-red binding phenotype of an ::Tn5 mutant, suggesting that the effect of CsrB on biofilms may require RcsB. These results underscore the regulatory and compositional differences between and biofilms. By activating CsrB expression, the BarA/UvrY two-component system has pleiotropic effects that impact biofilm production and stability.