Prevalence of Antibiotic and Metal Resistance Genes in Phytoremediated Cadmium and Zinc Soil Assisted by Chitosan and Trichoderma Harzianum

Abstract

Heavy metal in soil can be toxic with high concentrations and acts as selective pressure for both bacterial metal and antibiotic resistance, posing a serious risk to public health. In cadmium (Cd) and zinc (Zn) contaminated soil, chitosan (Chi) and Trichoderma harzianum (Tri) was applied alone and in combination to assist phytoremediation by Amaranthus hypochondriacus L. Prevalence of soil antibiotic and metal resistance genes (ARGs and MRGs) 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 increasd availability of Cd and Zn in soil. Meanwhile, combination of Chi and Tri enhanced the prevalence of ARGs (e.g., multidrug and β-lactams 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.

Keywords: Heavy metal fractions, co-selection, mobile genetic elements, bacterial host, network analysis