Background: We have previously identified a pair of bacterial two-component system RssA-RssB involved in regulation of Serratia marcescens swarming. Further studies showed that RssA-RssB signaling is growth phase dependent, being inactivated at early logarithmic phase for a period of about 30 min. During this period, expression of the flagellar master regulatory operon flhDCSm whose transcriptional regulation is under direct control of RssB is increased due to derepression. In this article, the environmental toxic compounds, including benzene, ethyl benzene, toluene, and xylene (BTEX) were found to show clearly negative effect on S. marcescens CH-1 swarming. The expression of flhDCSm and synthesis of flagellum were decreased accordingly. Whether the BETX compounds at non-lethal concentration can affect the signaling status of RssA-RssB and subsequently repress the expression level of flhDCSm was evaluated. Using the S. marcescens CH-1 (pflhDCsm::luxCDABE), the biosensor strain grown to early logarithmic phase as the reporter strain, results showed that increase of flhDCSm expression level was inhibited in the presence of BTEX compounds in a dose-dependent manner. Subsequent detection of contaminated water samples taken from a industry waste water showed clear reduction of light emission in comparison with the uncontaminated waters. Thus this strain bears the potential of being developed to be a biosensor strain for use in a upset early warning device (UEWD) for rapid detection of contaminated water.