Unveiling the chemotactic response and mechanism of Shewanella oneidensis MR-1 to nitrobenzene

Bioreduction by electroactive bacteria (EAB) is considered as a potential and cost-effective approach for the removal of nitroaromatic compounds (NACs). However, little is known about how the widespread EAB sense and respond to slightly soluble NACs in aquatic environments. Here, the chemotactic behaviors of Shewanella oneidensis MR-1, a model EAB, toward several NACs were examined and their underlying molecular mechanism was elucidated. S. oneidensis MR-1 was found to exhibit a strong chemotactic response to nitrobenzene (NB), but not to other selected NACs under aerobic conditions. To sense NB, this bacterium requires both the histidine kinase (CheA-3)-involved chemotactic signal transduction pathway and an inner-membrane c-type cytochrome CymA. Such a chemotactic response is mediated by an energy taxis mechanism. Additionally, external riboflavin was shown to greatly enhance the Shewanella taxis toward NB, implying a feasible way to increase the bioavailability of NACs. The present study deepens our understanding of the role of microbial chemotaxis in the removal of NACs and provides more options for the bioremediation of NAC-contaminated sites.