Enhanced phytoremediation of PCBs-contaminated soil by co-expressing tfdB and bphC in Arabidopsis aiding in metabolism and improving toxicity tolerance

Abstract

Phytoremediation is a promising method for decontaminating polychlorinated biphenyls (PCBs) in the soil and environment. However, the efficiency of phytoremediation is hindered as PCBs can also cause toxicity towards plants used for the remediation and the low solubility of PCBs prevents them from being absorbed from the soil. To improve the efficiency of phytoremediation, a transgenic Arabidopsis thaliana was constructed by expressing two exogenous genes: tfdB (1771 bp), responsible for encoding 2, 4-dichlorophenol hydroxylase, and bphC (900 bp), responsible for encoding 2,3-dihydroxybiphenyl-1,2-dioxygenase. These play crucial roles in breaking down the biphenyl ring and hydroxylation of biphenyl derivatives. The removal efficiency and plant tolerance under 2, 4-dichloro-1-(4-chlorophenyl) benzene (PCB28) stress were examined by conducting hydroponic and pot experiments. The results demonstrated that all transgenic lines exhibited higher tolerance indices and 50% inhibitory concentrations compared to the wild-type Arabidopsis. Additionally, transgenic plants displayed increased enzymatic activities of POD, SOD, and CAT under PCB28 stress in contrast to the untreated condition. Co-expression of the two genes tfdB and bphC in the plant showed superior resistance to plants expressing either tfdB or bphC. Compared to wild-type plants, co-expression of tfdB and bphC in A. thaliana increased removal rates of PCB28 from soil nearly twofold and reduced the residual amount in plants. The presence of 2,6-dichlorophenylacetic acid in transgenic tfdB+bphC A. thaliana suggested that these plants strengthened the metabolism of PCB28, which was similar to the benzoic acid metabolic-like pathway in microorganisms. This study demonstrated that co-expressing two genes holds great potential as an efficient alternative for alleviating PCB-induced toxicity stress on plants and enhancing phytoremediation efficiency.