Glutathione-dependent metabolism of electrophilic compounds by bacteria
The work presented investigates various aspects of glutathione-dependent electrophile metabolism in bacteria. First, we studied the response of Staphyloccocus aureus to the electrophile methylglyoxal. We found that under our experimental conditions, this organism is incapable of methylglyoxal metabolism by either glutatione-dependent or independent mechanisms. Glutatione was found to sensitise S. aureus to methylglyoxal. Furthermore, the sulphydryl group of glutathione is essential in this process. This implies that a glutathione conjugate may be involved in the increased sensitivity. Methylglyoxal does not activate K+ efflux from S. aureus cells, suggesting that the KefB K+ efflux system is absent from this organism. NEM activates a slow release of K+ indicating that the KefC system may be present. We investigated the response of E. coli and Pseudomonas sp. to the electrophilic herbicide alachlor. This compound activates a release of K+ from E.coli but not from any Pseudomona tested. K+ efflux is not mediated by KefB, KefC or the major mechanosensitive channels. In addition to the K+ efflux, alachlor stimulated an increase in the absorbance at 265 nm of media containing E. coli. It is not fully understood what this absorbance increase represents but it may reflect an increase in the solubility of alachlor over time. Despite its potential toxicity, alachlor did not affect the growth of either E. coli or P. fragi. However, when E. coli were treated with EDTA they became sensitive to alachlor. This result and data obtained using 14C-labelled alachlor indicated that alachlor does not normally enter E. coli cells. Finally, we investigated the response of E. coli expressing dcmA from Methylophilus sp. DM11 to DCM. Addition of DCM resulted in immediate cessation of growth, which was not due to formaldehyde accumulation. Cells washed free of DCM after a short incubation resume growth at the pre-addition rate, indicating DCM dehalogenation causes no permanent damage to the cell.