Biodetection of potential genotoxic pollutants entering the human food chain through ashes used in livestock diets

• A microbial biosensor based on recA promoter and firefly luciferase was built.
• This permits to detect genotoxicity of heavy metals alone or in complex mixtures.
• This could be used to evaluate the genotoxic risk of ashes added to livestock feeds.
• Among heavy metals polluting these ashes, Cr showed the strongest genotoxicity.

Ash derived from energy generation is used as a source of minerals in livestock feeds. The microbial biosensor recApr–Luc2 was built to detect genotoxic hazard in recycled ash. Escherichia coli SOS gene (recA, lexA, dinI and umuC) expression in response to cisplatin-induced DNA damage led to the selection of the recA promoter. The biosensor required functional RecA expression to respond to genotoxic heavy metals (Cr > Cd ≈ Pb), and polluted ash induced a strong recApr–Luc2 response. In human liver and intestinal cells, heavy metals induced acute toxicity (Cr > Cd > Pb) at concentrations sufficient to activate recApr–Luc2. Cytostatic effects, including genotoxicity, were cell- and metal-dependent, apart from Cr. In agreement with the recApr–Luc2 bioassay, Cr had the strongest effect in all cells. In conclusion, recApr–Luc2 could be useful for evaluating the genotoxic risk of pollutants present in ash that might be concentrated in animal products and, thus, entering the human food chain.