Evaluation of the promiscuous component of several bacterial export pumps TolC as a biomarker for toxic pollutants in feedstuffs

Abstract

A significant risk to the food chain is the presence of noxious pollutants in the feeds of animals whose products are used in human nutrition. Consequently, analytical methods and biosensors have been developed to detect these types of contaminates in feeds. Here we have evaluated whether the expression of TolC, a promiscuous component of several ATP-dependent efflux pumps in E. coli, up-regulated in response to chemical stress, could be a useful biomarker for this aim. Changes in TolC expression in response to toxic compounds, with different abilities to induce DNA damage, were determined using two E. coli strains with (DH5α) and without (BL21(DE3)) inactivating mutation in RecA gene. Deoxycholic acid and potassium dichromate up-regulated TolC in both strains. In contrast, cisplatin-induced TolC up-regulation was abolished in the absence of a functional RecA. When the effect of several insecticides, herbicides, antibiotics and common soil pollutants on TolC expression was analyzed, a relationship between toxicity and their ability to up-regulate TolC was observed. However, this was not a general event because the insecticide α-cipermetrin induced a reduction in cell viability, which was not accompanied by TolC up-regulation. In contrast, the soil pollutant benzene was able to stimulate TolC expression at non-toxic concentrations. When this test was used to analyze aqueous extracts from different feedstuffs, up-regulation of TolC was found in the absence of cell toxicity and was even accompanied by enhanced cell viability. In conclusion, TolC expression is partly dependent on the integrity of the RecA/LexaA system. Although toxic compounds up-regulate TolC in a dose-dependent manner, this response is also activated by non-toxic agents. Thus, owing to its poor specificity regardless of its sensitivity, the use of TolC up-regulation in E. coli to detect the presence of toxic pollutants in conventional and unconventional sources of nutrients for ruminant feeding requires supplementary biomarkers.

Keywords: Biosensor; Chemoresistance; Escherichia coli; Export pump; Food safety; Toxicity.