Phytoremediation of heavy metal and tetracycline co‐contaminated soil by Solanum nigrum L.: Response of tetracycline‐resistant genes

Abstract Co‐contamination with heavy metals (HMs) and tetracyclines (TCs) in soils has been widely reported and has resulted in serious consequences, such as the diffusion of tetracycline‐resistant genes (TRGs). Phytoremediation displays high potential for the remediation of co‐contaminated soils. Here, we chose a Cd hyperaccumulator ( Solanum nigrum L.) to explore the accumulation of HMs in plants and the effect of TRG diffusion in HM‐TC‐contaminated soil by conducting a pot experiment. The results showed that the shoot biomass of S. nigrum L. decreased by 28.39%–73.00% in treatments with HM (Cd and Cu) contamination singly caused by the toxicity of a nontarget element (Cu). The Cd concentrations in S. nigrum L. shoots increased by 30 times, while the Cu concentrations increased by less than 3 times. The bioconcentration factors (BCFs) and translocation factors (TFs) of Cd ranged from 1.05 to 7.98 and 0.80 to 2.27, respectively, which decreased with increasing TC concentrations in most treatments. The TC residuals in soils increased greatly with increasing TC and HM concentrations. Their concentrations in S. nigrum L. tissues followed the order chlorotetracycline > tetracycline > oxytetracycline. Phytoremediation stimulated the growth of soil microorganisms and increased the abundance of mobile genetic elements ( intI 1) and TRGs, especially efflux pump genes ( tet C and tet G, which increased 2.97 and 4.13 logs after phytoremediation, respectively). Our results suggested that phytoremediation had a high potential for HM and TC removal; however, it increased the diffusion risk of TRGs, especially for efflux pump genes that functioned in both HM and TC resistance.