H-NOX Regulates Biofilm Formation in Agrobacterium Vitis in Response to NO.

Transitions between motile and biofilm lifestyles are highly regulated and fundamental to microbial pathogenesis. H-NOX (heme-nitric oxide/oxygen-binding domain) is a key regulator of bacterial communal behaviors, such as biofilm formation. A predicted bifunctional cyclic di-GMP metabolizing enzyme, composed of diguanylate cyclase and phosphodiesterase (PDE) domains (_3097), is annotated downstream of an gene in S4. Here, we demonstrate that H-NOX is a nitric oxide (NO)-binding hemoprotein that binds to and regulates the activity of _3097 (HaCE; H-NOX-associated cyclic di-GMP processing enzyme). Kinetic analysis of HaCE indicates a ∼four-fold increase in PDE activity in the presence of NO-bound H-NOX. Biofilm analysis with crystal violet staining reveals that low concentrations of NO reduce biofilm growth in the wild-type S4 strain, but the mutant Δ strain has no NO phenotype, suggesting that H-NOX is responsible for the NO biofilm phenotype in . Together, these data indicate that H-NOX enhances cyclic di-GMP degradation to reduce biofilm formation in response to NO in .