Biogas slurry acts as a “microbial gatekeeper” to lower the spread risk of antibiotic resistance genes in soil-lettuce system

Abstract

The risk of antibiotic resistance genes (ARGs) from livestock manure has attracted extensive attention. However, the impacts of products at various stages of organic fertilizer production on ARGs in soil-lettuce system haven't been comprehensively evaluated. This study looked into the impacts of these products (cow manure, biogas slurry, biogas residue, and organic fertilizer) on transport and bioaccumulation of ARGs in soil-lettuce system by high-throughput quantitative PCR. Results showed that the relative abundance of ARGs in cow manure treatment (CM) and organic fertilizer treatment (OF) were reduced in soil (52.94 % and 41.18 %, respectively) compared to CK. Biogas slurry treatment (BS) had the lowest relative abundance of ARGs in all treatments with the value in root, inner leaf, and outer leaf being 0.07, 0.03, and 0.08 copies/16S rRNA gene copies, respectively (P < 0.05). For core ARGs, biogas residue treatment (BR) had the highest abundance in soil, while BS had the lowest abundance in plant parts. For high-risk ARGs, CM and OF treatments led to high abundance of aac(6′)-Ib-03 gene in soil, but BS treatment reduced the abundance of high-risk ARGs in lettuce. BS treatment exhibited a distinct bacterial network and fewer ARGs-bacteria correlations, probably due to the selective promotion of Proteobacteria and its nutrient cycling groups. ARGs were enriched in plant tissues (bioaccumulation factor (BAF) > 1) at CM and OF treatments, while were suppressed in aerial parts (inner and outer leaves) of BS, flooded with biogas slurry (BSF), and BR treatments. Overall, different products at various production stages have various effects on ARGs spreading in soil-plant system. BS and BR may be good at controlling ARGs spreading and provide guidance for waste treatment and agricultural production.