Responses of four Campylobacterales to cadmium stress

The tolerance to cadmium cations of four Campylobacterales species was determined and compared to understand better bacterial mechanisms of resistance to cadmium stress. Growth inhibition experiments indicated that there were differences between the susceptibilities to cadmium of the four bacterial species. Bioinformatic analyses showed that these bacteria had considerable repertoires of proteins that could be involved in cadmium ion detoxication, but the cadmium susceptibility of each of the Campylobacterales did not correlate with the putative molecular mechanisms to reduce intracellular cadmium concentration identified in each one of them. Rates of glutathione and thioredoxin reduction were measured in situ for each bacterium, and the modulation of these rates by exposure of the bacteria to cadmium were determined. Significant differences were observed between the changes in reduction rates induced by cadmium in the four Campylobacterales species, but these changes did not correlate with the inhibition of growth caused by cadmium stress. The results suggested that cadmium had multifactorial effects on the physiology of the four bacterial species that were not confined to mechanisms involved in export or complexation of cadmium cations.