| Antibiotic selective pressure could induce the production of antibiotic resistance genes(ARGs).The abuse of antibiotics in livestock farming led to livestock wastes becoming an important reservoir for ARGs in the environment.ARGs may be transferred to human pathogenic bacteria through horizontal gene transfer,which could reduce the efficacy of antibiotic therapies and threat human health.Aerobic composting is one of the main methods for recycling livestock manure,which is driven by various functional microorganisms(such as bacteria and fungi).Inoculating with exogenous functional microorganisms could improve the efficiency of composting and improve the quality of compost products,but the effects of microbial inoculation on microbial communities,ARGs,cellulose-degrading genes,and nitrogen-fixing genes during composting was unclear.The application of organic fertilizers in agricultural has become a main approach for transmitting ARGs to soil.ARGs in soil can enter plant endophyte and transport via the food chain.However,it was unclear that the accumulation and transport of the ARGs in soil and plant.Therefore,this study investigated the effects of inoculating with lignocellulose-degrading microorganisms and functional microorganisms on bacterial community,fungal community,diazotrophic community and ARGs,cellulose-degrading genes,nitrogen-fixing genes during composting.The relationships among functional genes,functional microorganism,and environmental factors were analyzed,and revealed the mechanism effects of inoculating with functional microorganism on microbial community and functional genes during composting.The pot experiments were conducted to study the transport and accumulation of ARGs in the fertilizer-soil-vegetable system during the application of organic fertilizers in vegetables.The microbial community of the soil and vegetables were analyzed,and the occurrence characteristics of ARGs and their relationship with microbial community were clarified,and further elucidate the underlying microbiological mechanisms of ARGs variation in soil and vegetables.The main results and conclusions are as follows.(1)Inoculation with lignocellulose-degrading microorganisms caused greater decreases in 6 ARGs and 3 mobile genetic elements than the control.The total relative abundances of ARGs in compost products decreased by 0.08 logs in the inoculation treatment but increased by 0.23 logs in the control.The bacterial community was clustered according to the composting time in the two treatments,where inoculation mainly affected the bacterial community during the mesophilic phase.Redundancy analysis and network analysis showed that the bacterial community succession had important effects on the variations in ARGs.Inoculation with lignocellulose-degrading microorganisms led to the reduction of ARGs,which was significantly correlated with the abundances of potential host bacteria for ARGs.Thus,inoculation with lignocellulose-degrading microorganisms could decrease the risk of ARGs spreading and make compost products more security.(2)Lignocellulose degradation rate in inoculation treatment was 8.77%–34.45% higher compared with control.Inoculation aff ected the distribution of the fungal community,increased the community diversity,and inhibited pathogens.Network analysis showed that inoculation changed the co-occurrence patterns of the fungal communities and made the co-composting system more stable.The relative abundances of glycoside hydrolase genes GH3 E,GH6,and GH7 were 0.45,0.09,and 0.39 logs higher in inoculation treatment,respectively,than control.Partial least-squares path modeling(PLS-PM)suggested that the variations in cellulose-degrading genes were driven mainly by changes in the fungal community during co-composting.Therefore,the lignocellulose-degrading consortium accelerated the transformation of lignocellulose to facilitate safer composting.(3)The nif H gene copy number was 17.50%-25.28% higher in inoculation treatment compared with control in the later phase.Inoculation changed the diazotroph community distribution,and increased the community diversity and complexity.Network analysis indicated that inoculation affected the diazotroph community co-occurrence patterns and the co-composting system was more stable.Partial least-squares path modeling showed that carbon sources and the diazotroph community mainly determined the increased abundance of the nif H gene.Inoculation with the lignocellulose-degrading consortium stimulated the diazotrophs activities.(4)Inoculating with functional microorganisms in the early and cooling phase could increase the temperature,prolong the thermophilic phase,reduce the bioavailability of Cu and Zn,and improve the quality of compost products.Compared with the control,inoculating with functional microorganisms inhibited the increase in the abundance of some ARGs,especially in the two-phase inoculation.The total abundance of ARGs decreased by 0.26 logs in two-phase inoculation treatment,and caused greater decreases in 8 ARGs and 3 MGEs.Inoculation mainly affected the bacterial community during the mesophilic and cooling phase.PLS-PM and network analysis showed that bacterial community and MGEs contributed greatly to the changes of ARGs.Inoculating with functional microorganisms could reduce the abundance of potential host bacteria of ARGs,thereby reducing the abundance of ARGs.(5)The application of organic fertilizer in vegetables showed that the abundance of ARGs in soil was significantly higher than that in vegetables.The application of organic fertilizers,especially untreated manure,could increase the abundance of ARGs and human pathogenic bacteria(HPB)in the soil,and had a stronger effect on ARGs in soil during vegetable cultivation than compost products.Untreated manure increased the accumulation of ARGs and some HPB in vegetables,while the compost products which inoculating with functional microorganisms reduced the abundance of ARGs by 0.51 and 0.54 logs in leaves of ruccola salad and cherry radish.The application of organic fertilizer increased the abundance of Bacteroidetes and decreased the Acidobacteria and Plantomytomytes in the soil.After vegetables have harvested,Proteobacteria is dominant in the soil,followed by Bacteroidetes,Actinobacteria and Acidobacteria.Cyanobacteria is the dominant bacteria in most vegetables,followed by Proteobacteria.PLS-PM and network analysis showed that the application of organic fertilizer could influence the HPB and MGEs which mediated the horizontal gene transfer,thus changing the transport of ARGs in soil.However,the changes of MGEs caused by bacterial community succession was the main mechanism affecting the accumulation of ARGs in vegetables.In conclusion,inoculating with functional microorganisms during the composting could increase the abundance of cellulose-degrading genes and nif H genes,reduce residual ARGs and MGEs in compost products,and improve the quality and safety of compost products.Untreated manure application increased the abundance of ARGs and HPB in soil and most vegetables,while compost products have less effect on ARGs in soil after vegetable cultivation,and could reduce the accumulation of ARGs in some vegetables.The results of this study provided theoretical basis for the harmless treatment and resource utilization of livestock waste. |
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