Absence of functional TolC protein causes increased stress response gene expression in Sinorhizobium meliloti

Abstract

BackgroundThe TolC protein from Sinorhizobium meliloti has previously been demonstrated to be required for establishing successful biological nitrogen fixation symbiosis with Medicago sativa. It is also needed in protein and exopolysaccharide secretion and for protection against osmotic and oxidative stresses. Here, the transcriptional profile of free-living S. meliloti 1021 tolC mutant is described as a step toward understanding its role in the physiology of the cell.ResultsComparison of tolC mutant and wild-type strains transcriptomes showed 1177 genes with significantly increased expression while 325 had significantly decreased expression levels. The genes with an increased expression suggest the activation of a cytoplasmic and extracytoplasmic stress responses possibly 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 the 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 for nutrient uptake suggests a higher metabolic rate of the tolC mutant. We also demonstrated increased swarming motility in the tolC mutant strain. Absence of functional TolC caused decreased expression mainly of genes encoding products involved in nitrogen metabolism and transport.ConclusionThis 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 act in concert to restore cell homeostasis. This finding further underlines the fundamental role of this protein in Sinorhizobium meliloti biology.

MdsABC-Mediated Pathway for Pathogenicity in Salmonella enterica Serovar Typhimurium

“…The overproduced MdsABC can complement the acrAB or tolC mutant to a certain degree, which is consistent with previous studies that showed that MdsAB assembles with TolC and confers bacterial resistance to antimicrobial dyes, such as acriflavine, crystal violet, methylene blue, and rhodamine 6G (13). It assists in exuding a wide range of extracellular and intracellular compounds to maintain bacterial homeostasis in concert with TolC-linked tripartite efflux pumps (7,23,24). Bacterial efflux pumps have a role in exporting not only abiotics such as antibiotics, detergents, and dyes but also host-derived antimicrobial agents.…”

The conserved polarity factor PodJ1 impacts multiple cell envelope‐associated functions in Sinorhizobium meliloti

“…SMc00067, SMc00122 and SMc03872 encode a lipoprotein, a penicillin‐binding protein and a protease, respectively, which may all participate in the modification of cell envelope structures; while SMc03855 encodes a 2‐methylthioadenine synthetase and SMc03996 a thiamine‐phosphate pyrophosphorylase, both cytoplasmic enzymes. Notably, the expression of SMc00067, SMc03855, SMc03872 and SMc3996 are all elevated in a tolC mutant, which exhibits heightened stress responses (Santos et al ., 2010). The final and most intriguing suppressor candidate is the orthologue of the C. crescentus membrane‐bound histidine kinase PleC, encoded by SMc02369 (39% identity, 57% similarity, with 74% coverage) (Hallez et al ., 2004; Johnson et al ., 2008; Brilli et al ., 2010).…”

Deletion of mtrC in Haemophilus ducreyi Increases Sensitivity to Human Antimicrobial Peptides and Activates the CpxRA Regulon

“…Deletion of individual genes encoding the AcrAAcrB-TolC pump in Salmonella enterica led to global changes in gene expression, including changes in virulence factor expression; the regulatory basis for these transcriptional changes is not known (53). Loss of the outer membrane channel TolC led to increased expression of several regulatory genes in E. coli (41), and the CpxRA system in Sinorhizobium meliloti was activated by mutagenesis of tolC (44). Rosner and Martin postulated that the effects of inactivating TolC are due to intracellular accumulation of metabolic products normally secreted through the TolC channel, although specific metabolites were not identified (41).…”