The Salmonella enterica sv. Typhimurium smvA, yddG and ompD (porin) genes are required for the efficient efflux of methyl viologen

Abstract

SummaryIn Gram-negative bacteria, a subset of inner membrane proteins in the major facilitator superfamily (MFS) acts as efflux pumps to decrease the intracellular concentrations of multiple toxic substrates and confers multidrug resistance. The Salmonella enterica sv. Typhimurium smvA gene encodes a product predicted to be an MFS protein most similar to QacA of Staphylococcus aureus . Like mutations in qacA , mutations in smvA confer increased sensitivity to methyl viologen (MV). Mutations in the adjacent ompD (porin) and yddG (drug/metabolite transporter) genes also confer increased sensitivity to MV, and mutations in smvA are epistatic to mutations in ompD or yddG for this phenotype. YddG and OmpD probably comprise a second efflux pump in which the OmpD porin acts as an outer membrane channel (OMC) protein for the efflux of MV and functions independently of the SmvA pump. In support of this idea, the pump dependent on YddG and OmpD has a different substrate specificity from the pump dependent on SmvA. Mutations in tolC , which encodes an OMC protein, confer increased resistance to MV. TolC apparently facilitates the import of MV, and a subset of OMC proteins including the OmpD porin and TolC may facilitate both import and export of distinct subsets of toxic substrates.

Molecular Basis of Bacterial Outer Membrane Permeability Revisited

“…Interestingly, the synthesis of this porin is dependent on cyclic AMP (B. Rotman and G. F.-L. Ames, personal communication). The gene ompD is located downstream of the putative transporter gene yddG, and recently the inactivation of either of these genes was reported to cause hypersusceptibility to methyl viologen (577). The authors propose that the OmpD porin forms a multiprotein complex with the YddG pump, playing the role of the exit channel like TolC.…”

KmrA Multidrug Efflux Pump from Klebsiella pneumoniae

“…It has been reported that SmvA is involved in resistance against methyl viologen 23) and acriflavine. 24) We cloned the smvA gene, introduced it into cells of the drug-hypersusceptible E. coli KAM32 host, and measured the MICs of various antimicrobial agents. E. coli KAM32/pSMVA3 (carrying smvA) showed elevated MICs of tetracycline, norfloxacin, acriflavine, ethidium bromide, methyl viologen, TPPCl and so on, compared with E. coli KAM32/pSTV28 (control) ( Table 1).…”

“…Thus, it is clear that KmrA belongs to the multidrug efflux pumps of the MF superfamily. 24) Proteins or hypothetical proteins that showed sequence similarity with KmrA are widely distributed in both Gram-negative and Gram-positive bacteria (Swiss-Prot database) including Erwinia, Pseudomonas, Streptococcus, Streptomyces, Mycobacterium, Nocardia and Corynebacterium. Among these bacterial genera, it seemed that many similar proteins (or hypothetical proteins) are present in Streptomyces (data not shown).…”

Bacillus subtilis Paraquat Resistance Is Directed by σ M , an Extracytoplasmic Function Sigma Factor, and Is Conferred by YqjL and BcrC

“…We have demonstrated that a M null mutant is more sensitive to a subfamily of superoxide-generating reagents related to PQ but not to other superoxide generators such as mena- (39). SmvA is similar to the MvrA protein of E. coli (17,29).…”