Diminishing Heavy Metal Co-Resistance Aids in Antibiotic Resistome Elimination from Livestock Manure

Recycling manure compost as organic fertilizer closes nutrients loops in crop-livestock system but spreads antibiotic resistance genes (ARGs) in soils, threatening food sanitation and environmental health. Heavy metals (HMs) in manure further complicate ARGs reduction in compost due to co-resistance and cross-resistance. Here, we conducted an in-depth investigation into the relationship between bioavailable HMs and ARGs using sequential extraction for HMs and high-throughput quantitative gene analysis. High-throughput qPCR revealed a 4.9-49.3 % increase in the relative abundance of ARGs and mobile genetic elements (MGEs) under HMs pressure. Additionally, the effectiveness of a supplementary DC electric field (5 V) in regulating HMs speciation and reducing ARGs during chicken manure composting was evaluated. The electric field decreased the bioavailability of Cu, Cr, and As by 18.9-37.4 % and reduced the relative abundance of ARGs and MGEs by 24.6 %. Network analysis, mantel test, and variation partitioning analysis indicated that the reduction of ARGs was primarily attributed to the alleviated co-selection pressure of HMs under the electric field. In conclusion, applying an electric field represents a practical and efficient method to facilitate ARGs reduction in composting systems, thereby offering important insights into the environmental risk assessment and control of agricultural ARGs.