Study On The Dynamics And Control Of Antibiotic Resistance Genes Change During Composting Of Agricultural Wastes

Antibiotic resistance genes(ARGs)carried by antibiotic resistant bacteria,are considered as emerging pollutants and one of the primary causes of antibiotic resistance.Due to their potential risks,they have gained significant attention worldwide in recent years.As the demand for animal meat and protein by humans continues to increase,the livestock and poultry breeding industry has rapidly developed,leading to a surge in ARGs in animal manure.This has caused genetic pollution in the breeding area and its surrounding environment,posing a substantial threat to human health.Aerobic composting is an effective method for the safe treatment of animal manure,however,there is still a risk of ARGs contamination in the soil environment with the long-term application of organic fertilizers.Therefore,optimizing aerobic composting technology,analyzing the relationship between ARGs and environmental factors,and improving the efficiency of ARGs removal are urgent and important practical issues that need to be addressed.In this study,the bibliometric method was used to identify the popular research topics and development trends regarding ARGs.A simulation of the entire process of antibiotic feeding to poultry in the wild was carried out,and composting experiments were conducted using fecal samples.Using 84 types of ARGs as the starting point,q PCR,gene chips,high-throughput sequencing,and other methods were used to systematically study the reduction pattern of ARGs by composting,and the effects of different treatment methods,such as chitosan and zeolite,on the types,quantity,abundance,and dynamics of microbial communities were explored.Additionally,we analyzed the mechanism of the effects of various antibiotics,heavy metals,and environmental factors on ARGs changes,to provide theoretical guidance for the production of harmless compost products and the resource utilization of agricultural and fishery waste.The main research findings are as follows:(1)Traditional aerobic composting can effectively reduce the quantity and abundance of ARGs,but the environmental risks associated with mobile genetic elements(MGEs),such as transposons,are higher.By using chicken manure and bran as agricultural waste for aerobic composting,and qualitatively detecting the original compost using PCR,the research results showed that 14types of ARGs,accounting for 23.3%of the total,were reduced in quantity after the composting process.Among the different types of antibiotics,β-lactams showed the greatest reduction in quantity.Among the different mechanisms of resistance,ARGs involved in antibiotic inactivation showed the greatest reduction in quantity.The overall abundance of ARGs decreased by 36.8%,with tetracycline resistance genes showing the greatest reduction at 64.0%.Among the detected MGEs,transposons showed stronger horizontal transfer ability than integrative elements,and there were significant or extremely significant positive correlations between multiple transposons and ARGs.(2)Addition of chitosan can accelerate compost maturation,significantly reduce heavy metal and antibiotic complex pollutants,and has a lower environmental risk.On the basis of original aerobic composting,the effects of zeolite and chitosan additives on the physicochemical properties,total and available heavy metal content,antibiotic content,and environmental risk of composting were studied.The addition of chitosan and zeolite promoted the activity of thermophilic microorganisms,which accelerated the high-temperature stage of composting.The chitosan-treated composting showed a removal rate of 100%for the antibiotic chlortetracycline(CTC)and 90.9%for the more difficult-to-remove antibiotic ofloxacin(OFX),thereby reducing the ecological environmental risk of CTC and OFX.Chitosan can significantly improve the removal rate of biologically available heavy metals,with a removal rate of 99.0%for biologically available copper,which is 25%higher than the control group(CK),and a removal rate of 84.5%for biologically available cadmium.(3)Addition of chitosan can further improve ARGs removal rate,and ARGs are most affected by changes in bacterial communities.On the basis of(2),changes in ARGs and bacterial communities were determined,and the relationship between physical and chemical factors,microbial diversity,and ARGs and MGEs was explored in combination with(2).The addition of chitosan can further reduce the quantity(by 20)and abundance(by 56.7%)of ARGs,and the effect is better than that of zeolite addition treatment(reducing by 11.1%).Microorganisms are the main hosts of ARGs.Network analysis showed that eight categories of ARGs and 27 bacterial genera have host relationships in our experiment.Peptoniphilus(Firmicutes)genus potentially contains up to 24 types of ARGs and MGEs,which is the genus with the highest types of ARGs and can resist multiple antibiotics while horizontally transferring ARGs between different genera,thereby greatly increasing environmental risk.In addition,RDA analysis showed that changes in bacterial communities were the main environmental factors affecting ARGs changes,followed by temperature(r~2=0.84)>bio-Cd(r~2=0.81)>p H(r~2=0.79)>bio-Cu(r~2=0.64)>OFX(r~2=0.60)>CTC(r~2=0.57).Therefore,in further research,controlling these key environmental variables can be used to control ARGs changes.In summary,this study proposes a new strategy for treating complex pollution in compost,including ARGs,bioavailable heavy metals,and antibiotics,building on previous research.The strategy aims to reduce the co-selection pressure of ARGs,minimize the spread of pollutants,and lower environmental risk,providing a theoretical basis and technological reference for reducing agricultural and fishery waste source pollution and producing harmless organic fertilizers.