Background The TolC protein from Sinorhizobium meliloti has previously been demonstrated to be required for establishing successful biological nitrogen fixation symbiosis with Medicago sativa. mediated by the sigma factor RpoH1 and protein homologues of the CpxRA two-component regulatory system of Enterobacteria, respectively. Stress conditions are probably caused by perturbation of the cell envelope. Consistent with gene expression data, biochemical analysis indicates that this tolC mutant suffers from oxidative stress. This is illustrated by the elevated enzyme activity levels detected for catalase, superoxide dismutase and glutathione reductase. The observed increase in the expression of genes encoding products involved in central metabolism and transporters Rabbit Polyclonal to c-Met (phospho-Tyr1003) for nutrient uptake suggests a higher metabolic rate of the tolC mutant. We also exhibited increased swarming motility in the Raltegravir tolC mutant strain. Absence of functional TolC caused decreased expression mainly of genes encoding products involved in nitrogen metabolism and transport. Conclusion This work shows how a mutation in the outer membrane protein TolC, common to many bacterial transport systems, affects expression of a large number of genes that take action in concert to restore cell homeostasis. This obtaining further underlines the fundamental role of this protein in Sinorhizobium meliloti biology. Background The outer membrane protein TolC belongs to a family of envelope proteins found in Gram-negative bacteria [1] and is essential for the export of a wide range of harmful substances such as antibiotics, dyes, disinfectants and natural substances produced by the hosts, including bile, hormones and defense molecules [2,3]. TolC is also required for Raltegravir export of a range of extracellular proteins such as metalloproteases, -hemolysins, lipases, enterotoxin II [4], the siderophore enterobactin [5], colicin uptake and secretion [6] and bacteriophage adsorption [7]. The TolC protein from Escherichia Raltegravir coli was also suggested as possibly involved in the efflux of not yet determined cellular metabolites [8]. Intracellular metabolite accumulation caused upregulation of several transcription factors including MarA, SoxS and Rob. These in turn upregulate TolC, leading to a decrease in metabolite concentration and restoration of cell homeostasis [8]. TolC family members are also required for colonization and persistence of bacteria in their host organisms. For example, Erwinia chrysanthemi [9] and Xylella fastidiosa [10]tolC mutants were unable to grow in planta and their virulence was severely compromised. TolC-deficient strains of Brucella suis [11] and Vibrio cholerae [12] also displayed an attenuation of contamination or colonization in animal models, respectively. The TolC protein of Salmonella enterica was shown to be required for efficient adhesion and invasion of epithelial cells and macrophages and to colonize poultry [13,14]. Webber and collaborators [13] exhibited that S. enterica mutants lacking acrA, acrB, or tolC genes encoding an efflux pump showed repression of operons involved in pathogenesis. Operons included chemotaxis, motility and type III secretion system genes, offering a possible explanation for the attenuated pathogenesis of these strains [13]. TolC protein of Sinorhizobium meliloti, the symbiotic partner of the leguminous herb Medicago sativa was recently characterised [15]. A S. meliloti tolC insertion mutant induced none or only very few nodules in M. sativa roots. Any nodules created were brownish-white, non-nitrogen fixing, in contrast to the pink elongated nitrogen fixing nodules created by wild-type S. meliloti 1021. The tolC gene mutation strongly affected the resistance phenotype to antimicrobial brokers of herb origin and induced higher susceptibility to osmotic and oxidative stresses. Analysis of extracellular proteins showed that calcium-binding protein WgeA (formerly ExpE1), endoglycanase ExsH and the putative hemolysin-type calcium-binding protein “type”:”entrez-protein”,”attrs”:”text”:”SMc04171″,”term_id”:”1174169300″,”term_text”:”SMC04171″SMc04171 were secreted in a TolC dependent manner. Another phenotype shown by the S. meliloti tolC mutant was absence of exopolysaccharides succinoglycan and galactoglucan from your culture supernatant [15]. Absence of galactoglucan in the tolC mutant is usually explained by the lack of WgeA protein secretion [16], but the contribution of TolC to succinoglycan production is so much not understood. Several phenotypes displayed by the S. meliloti tolC mutant strain illustrated the wide importance of this outer membrane protein to cellular functions. To better understand the contribution of TolC protein to S. meliloti cell physiology under free-living conditions, we investigated the effect of its inactivation around the transcriptome. Our data point towards an increased expression of genes encoding products involved in stress response, central metabolic pathways, and nutrient uptake transporters in the tolC mutant. Genes encoding products involved in nitrogen metabolism, transport and cell division displayed decreased expression. Results and Conversation Global changes in gene expression associated to a mutation in the tolC gene Cosme et al. [15] disrupted the S. meliloti 1021 tolC gene by inserting plasmid pK19mob2?HMB into its coding sequence, eliminating the last 102 nucleotides. This mutant, potentially expressing a truncated protein, displayed several phenotypes such as impaired symbiosis with Medicago, higher sensitivity to osmotic and oxidative stresses and absence of some extracellular proteins and exopolysaccharides [15]. Here, growth rates of wild-type and the tolC gene insertion mutant SmLM030-2 produced in GMS.