The adaptation of Rhizobium leguminosarum bv. phaseoli to oxidative stress and its overlap with other environmental stress responses

Abstract

Summary: This paper reports the adaptation of Rhizobium leguminosarum bv. phaseoli to oxidative stress and the investigation of its overlap with other environmental stress responses. Treatment of R. leguminosarum bv. phaseoli cells with low concentrations of either menadione (MD, a superoxide generating agent) or 1-chloro-2,4-dinitrobenzene (CDNB, which depletes GSH levels) induced an adaptive response which resulted in cells becoming resistant to subsequent treatment with high concentrations of these oxidative stress compounds. There was overlap between the adaptive response to MD-generated superoxide stress and the response previously demonstrated in this organism to H2O2 (A. J. Crockford, G. A. Davis & H. D. Williams, 1995, Microbiology 141, 843-851); pretreatment with H2O2 was protective against cell killing by MD and vice versa. In contrast, similar experiments indicated only a limited overlap between the responses to H2O2 and CDNB-mediated GSH depletion. It was also found that H2O2, but not MD or CDNB, adaptation protected cells against subsequent osmotic challenge and heat shock. Carbon-starved cells were more resistant to H2O2 and MD killing than exponentially growing cultures, but were more sensitive to CDNB-mediated GSH depletion. Therefore, this work shows that there is a substantial, but incomplete overlap between the responses of R. leguminosarum to different forms of oxidative and other environmental stresses.