Proteus mirabilis glutathione S-transferase B1-1 is involved in protective mechanisms against oxidative and chemical stresses

We investigated the effects of several xenobiotics, including antimicrobial agents and general stress factors such as starvation, heat and osmotic shock, on the modulation of expression of Proteus mirabilis glutathione S-transferase B1-1 (PmGST B1-1). The level of expression of PmGST B1-1 was established by both Western- and Northern-blot experiments. Our results show that several compounds can modulate expression of PmGST B1-1. The level of PmGST B1-1 increased when bacterial cells were exposed to a variety of stresses such as 1-chloro-2,4-dinitrobenzene, H2O2, fosfomycin or tetracycline. A knock-out gstB gene was also constructed using the suicide vector pKNOCK1ox-Ap. Successful inactivation of the wild-type gene was confirmed by PCR, DNA sequence analysis and Western blotting. Under normal culture conditions, this mutant was viable and displayed no significant phenotypic differences compared with the wildtype. However, viability tests revealed that the null mutant was more sensitive to oxidative stress in the form of H2O2 and to several antimicrobial drugs when compared with the wild-type. These results suggest that PmGST B1-1 has an active role in the protection against oxidative stress generated by H2O2 and it appears to be involved in the detoxification of antimicrobial agents.