Microbial organic fertilizer prepared by co-composting of Trichoderma dregs mitigates dissemination of resistance, virulence genes, and bacterial pathogens in soil and rhizosphere.

ABSTRACT

The use of manure, mycelium dregs and other waste as organic fertilizer is the main source of antibiotic resistance genes (ARGs) and pathogens in farmland. Composting of waste may effectively remove ARGs and pathogens. However, the profiles and drivers of changes in metal resistance genes (MRGs), biocide resistance genes (BRGs), and virulence genes (VGs) in soil-crop rhizosphere systems after compost application remain largely unknown. Here, we prepared two kinds of microbial organic fertilizers (MOF) by using Trichoderma dregs (TDs) and organic fertilizer mixing method (MOF1) and TDs co-composting method (MOF2). The effects of different types and doses of MOF on resistance genes, VGs and pathogens in soil-rhizosphere system and their potential mechanisms were studied. The results showed that co-composting of TDs promoted the decomposition of organic carbon and decreased the absolute abundance of ARGs and mobile genetic elements (MGEs) by 53.4-65.0%. MOF1 application significantly increased the abundance and diversity of soil ARGs, BRGs, and VGs, while low and medium doses of MOF2 significantly decreased their abundance and diversity in soil and rhizosphere. Patterns of positive co-occurrence between MGEs and VGs/MRGs/BRGs/ARGs were observed through statistical analysis and gene arrangements. ARGs/MRGs reductions in MOF2 soil were directly driven by weakened horizontal gene transfer triggered by MGEs. Furthermore, MOF2 reduced soil BRGs/VGs levels by shifting bacterial communities (e.g., reduced bacterial host) or improving soil property. Our study provided new insights into the rational use of waste to minimize the spread of resistomes and VGs in soil.