| The residues of heavy metals and antibiotics in livestock and poultry waste are prominent and bring environmental problems,which need to be paid enough attention.The main reason is that the heavy metals and antibiotics are discharged into the environment with feces due to incomplete absorption of the animals,inducing the generation and spread of resistance genes.Without reasonable harmless treatment,it will pose a serious threat to the environment and human health.Aerobic composting is one of the effective means of harmless and resource recovery of livestock and poultry manure,which can prevent antibiotics from entering the environment at source,and are still uncertain about the elimination of resistance genes.It has not been determined whether the changes of resistance genes during composting are related to the microbial composition and resistance genes in the animal body,especially in the gut.In view of this,this paper takes chicken feed-tissue-gut-feces compost as the main line,to study the distribution and change of heavy metals,antibiotics and antibiotic resistance genes(ARGs)in the whole process and analyze the microbial community composition.On this basis,we analysis the relationship between target heavy metals,antibiotics,ARGs and microbiota,and ascertain regulation mechanism of the former three.The main results are as follows:1.The distribution of five heavy metals among chicken body-gut-manure composting system was related to feed supplemental level and heavy metal species.The distribution of heavy metals in different tissues of the chicken body was different.the concentrations of Zn,Cr and Pb were the highest in chicken liver,while Cu and Cd were the highest in muscles.The concentration of heavy metals in chicken gut was significantly higher than that in chicken tissues.The changes of different heavy metals in the gut varied with the prolongation of feeding period,and were affected by the existence of antibiotics.During the composting process,the total amount of heavy metals increased and the available decreased,which was significantly correlated with the moisture content,p H,carbon and nitrogen of compost.2.The intake of antibiotics led to some enrichment in the chicken tissues.Wherein the residues of chlorotetracycline and enrofloxacin in chicken tissues followed by liver>muscle>blood,and enrofloxacin was more easily enriched in tissues than chlorotetracycline.The enrichment of antibiotics in the gut was faster at first and then slower,and the residual concentration in the gut far exceeded the contents in tissues.However,most of antibiotics cannot be absorbed by the chicken body and discharged with chicken feces.The composting effectively reduced the concentrations of antibiotics in the feces.The degradation rates of chlortetracycline and enrofloxacin during composting were more than 80% and 60%,respectively.The reduction of compost on antibiotics was affected by compost materials,types of antibiotics,and physicochemical properties.And biochar addition could significantly improve the degradation rate of enrofloxacin.3.The diversity of ARGs in the feed-gut-compost system increased progressively,but the distribution of ARGs in chicken tissues was very low.The main subtypes of ARGs in different media exhibited significant differences,mainly tetracyclines and multidrug resistance genes,and the resistance mechanism was mainly antibiotic enzyme inactivation,efflux pump and ribosome protection.Composting could reduce the abundance of most ARGs and heavy metal resistance genes(HMRGs).The transmission of ARGs and HMRGs during composting is related to mobile gene elements(MGEs).Inc N and tnp A mainly mediated the resistance genes whose mechanisms were ribosome protection and efflux pump.Inc W,IS613,Int I1 and Int I2 mediate the resistance genes whose mechanisms were mainly enzyme inactivation and partly efflux pump.4.Proteobacteria,Bacteroides,Actinomycetes and Firmicutes were the main bacterial phylum among chicken body-gut-manure composting system,and their changes were affected by heavy metals,antibiotics,composting materials and physicochemical properties,and directly affected the distribution and propagation of ARGs.Most of the pathogens in the system were multidrug-resistant bacteria.Composting at high temperature and biochar addition could reduce the abundance of pathogens and the related ARGs,but could not completely remove them.The occurrence and change of ARGs in the composting process were related to the microbial composition and the presence of ARGs in the chicken body,especially in the gut,but the correlation was not significant.In conclusion,this study clarified the distribution of heavy metals,antibiotics and resistance genes and their relationship with bacterial community composition in the process of chicken body tissues,gut and feces composting,and elucidated the reduction regulatory mechanism of antibiotics and resistance genes.The residual distribution of heavy metals and antibiotics in the whole system of "chicken bodygut-chicken manure composting" was related to the supplemental level of feed,while the distribution of ARGs and microbial community had no significant correlation with the distribution of them in feed.These results would provide theoretical support for efficient reduction of antibiotics and resistance genes in chicken body-gut-manure composting system. |
PDF Full Text Request