Prevalence of antibiotic and metal resistance genes in phytoremediated cadmium and zinc contaminated soil assisted by chitosan and Trichoderma harzianum

Heavy metal in soil have been shown to be toxic with high concentrations and acts as selective pressure on both bacterial metal and antibiotic resistance determinants, posing a serious risk to public health. In cadmium (Cd) and zinc (Zn) contaminated soil, chitosan (Chi) and Trichoderma harzianum (Tri) were applied alone and in combination to assist phytoremediation by Amaranthus hypochondriacus L. Prevalence of antibiotic and metal resistance genes (ARGs and MRGs) in the soil was also evaluated using metagenomic approach. Results indicated that the phytoremediation of Cd and Zn contaminated soil was promoted by Chi, and Tri further reinforced this effect, along with the increased availability of Cd and Zn in soil. Meanwhile, combination of Chi and Tri enhanced the prevalence of ARGs (e.g., multidrug and β-lactam resistance genes) and maintained a high level of MRGs (e.g., chromium, copper) in soil. Soil available Zn and Cd fractions were the main factors contributing to ARGs profile by co-selection, while boosted bacterial hosts (e.g., Mitsuaria, Solirubrobacter, Ramlibacter) contributed to prevalence of most MRGs (e.g., Cd). These findings indicate the potential risk of ARGs and MRGs propagation in phytoremediation of metal contaminated soils assisted by organic and biological agents.