Redundancy in Periplasmic Binding Protein-Dependent Transport Systems for Trehalose, Sucrose, and Maltose in Sinorhizobium meliloti

摘要: The gram-negative soil bacterium Sinorhizobium meliloti is able to interact with the roots of Medicago sativa (lucerne or alfalfa) form nitrogen-fixing nodules and survive as a free-living saprophytic in soil. To successfully saprophyte, it must have ability compete other microorganisms for limited nutrient resources cope different abiotic stresses, such osmotic stress. As bacterium, S. can be exposed many molecules originating from bacteria, insects, plants, fungi. For example, more than 400 been identified alfalfa that may become available through exudation decomposition (36). One these compounds disaccharide trehalose [α-d-glucopyranosyl-(1,1)-α-d-glucopyranoside] (13, 36), well-known osmoprotectant found organisms (11). Trehalose occurs plant tissues colonized by microorganisms, mycorrhizal (41), symbiotic structures, including formed legumes response rhizobial infection 34). Under nonstress conditions, take up use its sole carbon energy source (17). various stress synthesizes accumulates trehalose, which serve compatible solute (7, 22). In cultures grown at high osmolarity, exogenous stimulates accumulation intracellular (43); this has decrease generation time (18). A variety mechanisms transport documented prokaryotes. Salmonella enterica serovar Typhimurium, transported via two pathways: mannose-specific IIMan enzyme phosphoenolpyruvate:carbohydrate phosphoenoltransferase system (PTS) galactose permease pathway (37). Escherichia coli systems uptake are differentially used depending upon osmolarity medium. conditions hydrolyzed periplasmic trehalase glucose, taken II PTS specific glucose (5). At low PTS-dependent IITre (27). Evidence similar also reported Vibrio parahaemolyticus (28). hyperthermophilic archaeon Thermococcus litoralis, gene cluster encodes maltose/trehalose (24) homology malEGFK E. coli. This belongs family binding protein-dependent ATP-binding cassette (BPD ABC systems) normally consist high-affinity substrate-binding protein located periplasm, hydrophobic membrane proteins, cytoplasmic ATP-hydrolyzing subunits (6). Willis Walker (47) operon aglEFGAK sugar involved α-glucoside disaccharides sucrose, maltose, trehalose. However, since agl mutants were utilize disaccharides, existence least one additional α-glucosides was suggested (47). In genome there predicted 430 over half on megaplasmid pSymB (12). report, we demonstrate an four genes pSymB, called thuEFGK, encoding proteins belonging superfamily BPD transporters, second (47). By mutational analysis growth studies, show thuEFGK sucrose. Despite their substrate overlap induced only whereas algEFGAK sucrose presumably Furthermore, here mutant severely impaired colonize roots, nodulation nitrogen fixation not affected.