CelR, an Ortholog of the Diguanylate Cyclase PleD of Caulobacter, Regulates Cellulose Synthesis in Agrobacterium tumefaciens

Cellulose fibrils play a role in attachment ofAgrobacterium tumefaciens to its plant host. While the genes for cellulose biosynthesis in the bacterium have been identified, little is known concerning the regulation of the process. The signal molecule cyclic di-GMP (c-di-GMP) has been linked to the regulation of exopolysaccharide biosynthesis in many bacterial species, includingA. tumefaciens . In this study, we identified two putative diguanylate cyclase genes,celR (atu1297 ) andatu1060 , that influence production of cellulose inA. tumefaciens . Overexpression of either gene resulted in increased cellulose production, while deletion ofcelR , but notatu1060 , resulted in decreased cellulose biosynthesis.celR overexpression also affected other phenotypes, including biofilm formation, formation of a polar adhesion structure, plant surface attachment, and virulence, suggesting that the gene plays a role in regulating these processes. Analysis ofcelR and Δcel mutants allowed differentiation between phenotypes associated with cellulose production, such as biofilm formation, and phenotypes probably resulting from c-di-GMP signaling, which include polar adhesion, attachment to plant tissue, and virulence. Phylogenetic comparisons suggest that species containing bothcelR andcelA , which encodes the catalytic subunit of cellulose synthase, adapted the CelR protein to regulate cellulose production while those that lackcelA use CelR, called PleD, to regulate specific processes associated with polar localization and cell division.