The Exopolysaccharide Cepacian Plays a Role in the Establishment of the - Symbiosis.

is a rhizobial strain that belongs to the beta-proteobacteria, a group known to form efficient nitrogen-fixing symbioses within root nodules of several legumes, including the agriculturally important common bean. The establishment of the symbiosis requires the exchange of rhizobial and plant signals such as lipochitooligosaccharides (Nod factors), polysaccharides, and flavonoids. Inspection of the genome of the competitive rhizobium revealed the presence of several polysaccharide biosynthetic gene clusters. In this study, we demonstrate that , a gene encoding a GDP-D-mannose 4,6-dehydratase, which is involved in the production of the exopolysaccharide cepacian, an important component of biofilms produced by closely related opportunistic pathogens of the complex (), is required for efficient plant colonization. Wild-type was shown to produce cepacian while a mutant did not. Additionally, the mutant produced a significantly lower amount of biofilm and formed less root nodules compared to the wild-type strain with as host plant. Finally, expression of the operon containing was induced by the presence of germinated seeds under nitrogen limiting conditions suggesting a role of this polysaccharide in the establishment of this ecologically important symbiosis.