Novel mixed-linkage ?-glucan activated by c-di-GMP in Sinorhizobium meliloti.

ABSTRACT: An artificial increase of cyclic diguanylate (c-di-GMP) levels in Sinorhizobium meliloti 8530, a bacterium that does not carry known cellulose synthesis genes, leads to overproduction of a substance that binds the dyes Congo red and calcofluor. Sugar composition and methylation analyses and NMR studies identified this compound as a linear mixed-linkage (1 ? 3)(1 ? 4)-?-D-glucan (ML ?-glucan), not previously described in bacteria but resembling ML ?-glucans found in plants and lichens. This unique polymer is hydrolyzed by the specific endoglucanase lichenase, but, unlike lichenan and barley glucan, it generates a disaccharidic ? 4)-?-D-Glcp-(1 ? 3)-?-D-Glcp-(1 ? repeating unit. A two-gene operon bgsBA required for production of this ML ?-glucan is conserved among several genera within the order Rhizobiales, where bgsA encodes a glycosyl transferase with domain resemblance and phylogenetic relationship to curdlan synthases and to bacterial cellulose synthases. ML ?-glucan synthesis is subjected to both transcriptional and posttranslational regulation. bgsBA transcription is dependent on the exopolysaccharide/quorum sensing ExpR/SinI regulatory system, and posttranslational regulation seems to involve allosteric activation of the ML ?-glucan synthase BgsA by c-di-GMP binding to its C-terminal domain. To our knowledge, this is the first report on a linear mixed-linkage (1 ? 3)(1 ? 4)-?-glucan produced by a bacterium. The S. meliloti ML ?-glucan participates in bacterial aggregation and biofilm formation and is required for efficient attachment to the roots of a host plant, resembling the biological role of cellulose in other bacteria.

SUBMITTER: Perez-Mendoza D 

PROVIDER: S-EPMC4343143 | biostudies-literature | 2015 Feb

REPOSITORIES: biostudies-literature