Dynamics Of Bacterial Communities And Its Correlation With Heavy Metals,Antibiotics And Nutrients In Chicken Manure Composting

Environmental pollution caused by manure which generated from intensive chicken farm has become an increasingly serious problem.In order to investigate the dynamics of bacterial communities,nutrients,heavy metals,antibiotics and antibiotic resistance genes?ARGs?during chicken manure composting,and explain the correlations between bacterial communities and nutrients,heavy metals,antibiotics and ARGs,the samples of fresh chicken manure and its composts,and fertilized soils were collected.The dynamics of bacterial communities were analyzed by using 16S rRNA high-throughput sequencing,while the relative abundance of potential pathogens and probiotics was investigated.The contents of nutrients,heavy metals,antibiotics were determined and analyzed.Besides,17 ARGs were tested by PCR,and5 ARGs were tested by qPCR.Correlation analysis was conducted between nutrients,heavy metals,antibiotics,ARGs and bacterial communities,in order to explain the effect of nutrients,heavy metals,antibiotics on bacterial communities and ARGs.The high-throughput sequencing indicated that the main phyla were Firmicutes,Proteobacteria,Actinobacteria and Bacteroidetes in groups of composting,and Proteobacteria,Acidobacteria and Firmicutes in soil.At genus level,each group had different dominant species.In group FM,FC,SC,Pd,FS and CS,the most abundant genera were Bacteroides?12.9%?,Pseudomonas?7.9%?and Ignatzschineria?7.9%?,Paucisalibacillus?6.8%?,Halomonas?14.3%?,unidentified_Acidobacteria?1.6%?and Sphingomonas?1.6%?,respectively.10 potential pathogenic bacteria and 10potential probiotics were observed.During composting,the total potential pathogenic bacteria decreased from 37.2%to 3.4%and the probiotics increased from 5.8%to7.1%.After fertilization,the total potential pathogens reduced to 0.91%in soil.The heavy metal contents fluctuated in different sample groups.Comparing with FM,the concentrations of all heavy metals increased after composting.In soil samples?FS and CS?,with the exception of Cd,no clear difference was observed between FS and CS?p>0.05?.Besides,the heavy metal contents As,Cr,Ni,and Pb were higher and Zn and Cu were lower in soil samples compared to Pd.During composting process,the contents of different antibiotics were varied.In FM,SDZ and ENR showed the highest?10.98 mg/kg?and lowest?0.05 mg/kg?average concentrations.After composting,concentrations of all antibiotics decreased,in which OFL,ENR and OTC decreased significantly?p<0.05?,and no SDZ and DC were detected in Pd.In soil samples,no SDZ,DC and OTC were detected,while the concentration of ENR and AMP were significantly higher in FS compared with those in CS?p<0.05?.In general,the detection rates of ARGs were higher in FM,at 50%-100%.Besides,composting process had a significant effect on the reduction of tetracycline resistance genes,and these genes were not found in Pd.According to the results of qPCR,ARGs erm B and aac?6'?-Ib-cr decreased significantly?p<0.05?in Pd,whereas no bla_CTX-MTX-M gene was detected in Pd.However,sul1 and tet M genes increased in Pd.For soil samples,no aac?6'?-Ib-cr gene was detected.Notably,the relative abundances of sul1,ermB and tetM were significantly lower in FS than in CS?p<0.05?.During composting process,the pH value,total potassium?TK?and phosphorus?TP?gradually increased and were significantly higher in Pd?p<0.05?.The contents of organic matter?OM?and the total nitrogen?TN?fluctuated during composting process and decreased significantly in Pd?p<0.05?.After fertilization,the content of TN rose by 0.05 g/kg,and TK and TP were significantly increased to 14.98 g/kg and1.59 g/kg?p<0.05?.According to the correlation analysis between environment factors and bacterial communities,the alpha diversities of communities showed significant correlation with heavy metals and nutrients?p<0.05?.CCA analysis revealed that bacterial community structure was most affected by heavy metals.VPA analysis showed that variation in the bacterial community structure was explained by environment factors,and heavy metals were the dominant contributor,which accounted by 54.75%,and followed by antibiotics?46.04%?and nutrients?33.87%?.Furthermore,Atopostipes,Corynbacterium₁ and Psychrobacter were found to have significant positive correlations with the heavy metal Cu and certain ARGs,antibiotics and nutrients.Correlation analysis revealed that certain antibiotics,heavy metal,and nutrients were significantly positive correlated with ARGs?p<0.05 or<0.01?.Overall,our results indicated that composting process is effective for reducing bacterial pathogens,antibiotics and ARGs,though there are still residues.The application of compost benefits the pathogens and ARGs reduction as well as probiotics and nutrients accumulation in soil.The results also highlighted that environment factors directly or indirectly affected the variations of ARGs in bacteria,while the variation of bacterial structure could affect ARGs.