Regulation of -Butyl Hydroperoxide Resistance by Chromosomal OhrR in ATCC 19606.

In this study, we show that ATCC 19606 harbors two sets of genes, respectively encoded in chromosomal DNA and a pMAC plasmid. We found no significant difference in organic hydroperoxide (OHP) resistance between strains with or without pMAC. However, a disk diffusion assay conducted by exposing wild-type, , represented gene on chromosome, or single mutants, or -- double mutants to -butyl hydroperoxide (BHP) found that the genes, represented genes on pMAC plasmid, may be able to complement the function of their chromosomal counterparts. Interestingly, single mutants generated in ATCC 17978, which does not harbor pMAC, demonstrated delayed exponential growth and loss of viability following exposure to 135 μg of BHP. In a survival assay conducted with larvae, these mutants demonstrated almost complete loss of virulence. Via an electrophoretic mobility shift assay (EMSA), we found that OhrR-C was able to bind to the promoter regions of both chromosomal and pMAC - genes, but with varying affinity. A gain-of-function assay conducted in showed that OhrR-C was not only capable of suppressing transformed genes but may also repress endogenous enzymes. Taken together, our findings suggest that chromosomal genes act as the major system in protecting ATCC 19606 from OHP stresses, but the genes on pMAC can provide a supplementary protective effect, and the interaction between these genes may affect other aspects of bacterial viability, such as growth and virulence.