SyrM is Involved in the Determination of the Amount and the Ratio of the Two forms of Exopolysaccharide EPSI in Rhizobium meliloti

Abstract

During the formation of nitrogen-fixing root nodule signal molecules controlling the specificity of the plant-bacterium interaction are exchanged. For the invasion of the nodule cells of alfalfa the exopolysaccharide (EPSI) of Rhizobium meliloti is required. The nodule invasion ability of exo mutants deficient in EPSI production can be partially restored by the addition of purified low molecular weight (LMV) fraction of EPSI (Battisti et al. 1992). Nitrogen starvation of the wild type R. meliloti results in an increase of EPSI production (Doherty et al. 1988). We have shown that the transcription of two exo genes, exoF and exoP was under the control of nitrogen, while the exoH and exoK genes were expressed independently of the nitrogen concentration. In the wild type R. meliloti the presence of nitrogen altered also the ratio of the HMW and LMW forms of EPSI favouring the production of LMW molecules.KeywordsWild Type StrainNitrogen ConcentrationMain FormNodule CellEPSI ProductionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.