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Int. J. Mol. Sci. 2011, 12(11), 7898-7933; doi:10.3390/ijms12117898
Review

Environmental Signals and Regulatory Pathways That Influence Exopolysaccharide Production in Rhizobia

Received: 29 August 2011; in revised form: 4 November 2011 / Accepted: 7 November 2011 / Published: 15 November 2011
(This article belongs to the Section Biochemistry, Molecular Biology and Biophysics)
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Abstract: Rhizobia are Gram-negative bacteria that can exist either as free-living bacteria or as nitrogen-fixing symbionts inside root nodules of leguminous plants. The composition of the rhizobial outer surface, containing a variety of polysaccharides, plays a significant role in the adaptation of these bacteria in both habitats. Among rhizobial polymers, exopolysaccharide (EPS) is indispensable for the invasion of a great majority of host plants which form indeterminate-type nodules. Various functions are ascribed to this heteropolymer, including protection against environmental stress and host defense, attachment to abiotic and biotic surfaces, and in signaling. The synthesis of EPS in rhizobia is a multi-step process regulated by several proteins at both transcriptional and post-transcriptional levels. Also, some environmental factors (carbon source, nitrogen and phosphate starvation, flavonoids) and stress conditions (osmolarity, ionic strength) affect EPS production. This paper discusses the recent data concerning the function of the genes required for EPS synthesis and the regulation of this process by several environmental signals. Up till now, the synthesis of rhizobial EPS has been best studied in two species, Sinorhizobium meliloti and Rhizobium leguminosarum. The latest data indicate that EPS synthesis in rhizobia undergoes very complex hierarchical regulation, in which proteins engaged in quorum sensing and the regulation of motility genes also participate. This finding enables a better understanding of the complex processes occurring in the rhizosphere which are crucial for successful colonization and infection of host plant roots.
Keywords: exopolysaccharide synthesis; exo and pss genes; Sinorhizobium meliloti; Rhizobium leguminosarum; quorum sensing; motility; rhizobium-legume symbiosis exopolysaccharide synthesis; exo and pss genes; Sinorhizobium meliloti; Rhizobium leguminosarum; quorum sensing; motility; rhizobium-legume symbiosis
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Janczarek, M. Environmental Signals and Regulatory Pathways That Influence Exopolysaccharide Production in Rhizobia. Int. J. Mol. Sci. 2011, 12, 7898-7933.

AMA Style

Janczarek M. Environmental Signals and Regulatory Pathways That Influence Exopolysaccharide Production in Rhizobia. International Journal of Molecular Sciences. 2011; 12(11):7898-7933.

Chicago/Turabian Style

Janczarek, Monika. 2011. "Environmental Signals and Regulatory Pathways That Influence Exopolysaccharide Production in Rhizobia." Int. J. Mol. Sci. 12, no. 11: 7898-7933.


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