Dataset Information

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

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

Pérez-Mendoza Daniel D Rodríguez-Carvajal Miguel Ángel MÁ Romero-Jiménez Lorena L Farias Gabriela de Araujo Gde A Lloret Javier J Gallegos María Trinidad MT Sanjuán Juan J

Proceedings of the National Academy of Sciences of the United States of America 20150203 7

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 uniqu ...[more]

PMID: 25650430

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Project description:Sinorhizobium meliloti undergoes major lifestyle changes between planktonic states, biofilm formation, and symbiosis with leguminous plant hosts. In many bacteria, the second messenger 3',5'-cyclic di-GMP (c-di-GMP, or cdG) promotes a sessile lifestyle by regulating a plethora of processes involved in biofilm formation, including motility and biosynthesis of exopolysaccharides (EPS). Here, we systematically investigated the role of cdG in S. meliloti Rm2011 encoding 22 proteins putatively associated with cdG synthesis, degradation, or binding. Single mutations in 21 of these genes did not cause evident changes in biofilm formation, motility, or EPS biosynthesis. In contrast, manipulation of cdG levels by overproducing endogenous or heterologous diguanylate cyclases (DGCs) or phosphodiesterases (PDEs) affected these processes and accumulation of N-Acyl-homoserine lactones in the culture supernatant. Specifically, individual overexpression of the S. meliloti genes pleD, SMb20523, SMb20447, SMc01464, and SMc03178 encoding putative DGCs and of SMb21517 encoding a single-domain PDE protein had an impact and resulted in increased levels of cdG. Compared to the wild type, an S. meliloti strain that did not produce detectable levels of cdG (cdG(0)) was more sensitive to acid stress. However, it was symbiotically potent, unaffected in motility, and only slightly reduced in biofilm formation. The SMc01790-SMc01796 locus, homologous to the Agrobacterium tumefaciens uppABCDEF cluster governing biosynthesis of a unipolarly localized polysaccharide, was found to be required for cdG-stimulated biofilm formation, while the single-domain PilZ protein McrA was identified as a cdG receptor protein involved in regulation of motility.We present the first systematic genome-wide investigation of the role of 3',5'-cyclic di-GMP (c-di-GMP, or cdG) in regulation of motility, biosynthesis of exopolysaccharides, biofilm formation, quorum sensing, and symbiosis in a symbiotic alpha-rhizobial species. Phenotypes of an S. meliloti strain unable to produce cdG (cdG(0)) demonstrated that this second messenger is not essential for root nodule symbiosis but may contribute to acid tolerance. Our data further suggest that enhanced levels of cdG promote sessility of S. meliloti and uncovered a single-domain PilZ protein as regulator of motility.

Dataset Information

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

Publications

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

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