The DsbA‐DsbB Disulfide Bond Formation System of Burkholderia cepacia Is Involved in the Production of Protease and Alkaline Phosphatase, Motility, Metal Resistance, and Multi‐Drug Resistance

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Abstract
In a previous study, we isolated a dsbB mutant of Burkholderia cepacia KF1 and showed that phenotypes of protease production and motility are dependent on DsbB, a membrane‐bound disulfide bond oxidoreductase. We have now isolated a dsbA mutant by transposon mutagenesis, cloned the dsbA gene encoding a periplasmic disulfide bond oxidoreductase, and characterized the function of the DsbA‐DsbB disulfide bond formation system in B. cepacia. The complementing DNA fragment had an open reading frame for a 212‐amino acid polypeptide with a potential redox‐active site sequence of Cys‐Pro‐His‐Cys that is homologous to Escherichia coli DsbA. The dsbA mutant, as well as the previously isolated dsbB mutant, was defective in the production of extracellular protease and alkaline phosphatase, as well as in motility. In addition, mutation in the DsbA‐DsbB system resulted in an increase in sensitivity to Cd2+ and Zn2+ as well as a variety of antibiotics including β‐lactams, kanamycin, erythromycin, novobiocin, ofloxacin and sodium dodecyl sulfate. These results suggested that the DsbA‐DsbB system might be involved in the formation of a metal efflux system as well as a multi‐drug resistance system.