Novel mixed-linkage β-glucan activated by c-di-GMP in Sinorhizobium meliloti
Rodríguez Carvajal, Miguel Ángel
Araujo Farias, Gabriela de
Trinidad Gallegos, Maria
|Department||Universidad de Sevilla. Departamento de Química Orgánica|
|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 ...
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)-β-D-glucan (ML β-glucan), not previously described in bacteria but resembling ML β-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)-β-DGlcp-(1→3)-β-D-Glcp-(1→ repeating unit. A two-gene operon bgsBA required for production of this ML β-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 β-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 β-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)-β-glucan produced by a bacterium. The S. meliloti ML β-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.
|Citation||Pérez-Mendoza, D., Rodríguez-Carvajal, M.Á., Romero-Jiménez, L., De Araujo Farias, G., Lloret, J., Trinidad Gallegos, M. y Sanjuan, J. (2015). Novel mixed-linkage β-glucan activated by c-di-GMP in Sinorhizobium meliloti. Proceedings of the National Academy of Sciences of the United States of America, 112 (7), E757-E765.|