The Effects Of Adding Corn Cobs On The Abundances Of Antibiotics Resistance Genes During Anaerobic Digestion Of Dairy Manure

Adding cellulose in the anaerobic digestion of livestock manure is one of the main technologies to improve the utilization of manure resources.It not only improves energy production efficiency,but also has a certain impact on the antibiotic resistance genes(ARGs)present in the manure.We carried out the anaerobic digestion tests of dairy manure at medium temperature(35℃),high temperature(55℃)and ultra high temperature(65℃),respectively,and set five corn cob contents of 0,4,8,12,16 g/L at each temperature,respectively.Totaling 3 kinds of ARGs,the tetracycline resistance genes(SRGs),sulfa resistance genes(TRGs),and macrolide resistance genes(MRGs)were used as the research objects to explore the effects of adding corn cobs on the changes in ARGs abundance during anaerobic digestion of dairy manure.The relationships between physicochemical factors,MGEs,microbial community and changes in ARGs were analyzed,and the internal microbial mechanisms that corn cobs affected ARGs changes at different temperatures were revealed.The main results and conclusions of the study were as follows:(1)With the increase of corncob content,the total gas production of anaerobic digestion at the three temperatures gradually increased,and the increase of gas production was the highest when the corncob content was 16 g/L at 55℃,reaching 124.07%.Adding corncobs at different temperatures had different effects on physicochemical factors: at 35℃ and 55℃ it reduced the SCOD removal rates,and at 65℃ it increased the SCOD removal rate.Only at 55℃ adding corncobs increased the utilization of VFAs,and when the corncob content was 16 g/L,the utilization rate was the highest,reaching 75.60%.(2)With the increase of corncob content,the total abundance of ARGs gradually decreased after digestion at 35℃ and 65℃.When the corncob content was 16 g/L at 65℃,the total abundance of ARGs decreased most,reaching 89.11%.The total abundance of ARGs after digestion at 55℃ gradually increased with the increase of corncob content,up to 290.10% at most.Compared with single manure,adding corncobs decreased the abundances of TRGs and MRGs after digestion at 35℃ and 65℃,but increased the abundances of TRGs and MRGs after digestion at 55℃.The abundance of SRGs after digestion at 65℃ decreased with the increase of corncob content,and the removal rate in S16 reached the highest value of 99.55%,and the abundances of SRGs changed irregularly at other temperatures.MGEs were mostly positively correlated with ARGs,and the decreases in the abundances of multiple ARGs were related to the reductions of the horizontal transfer of ARGs by MGEs.(3)Compared with the anaerobic digestion of single manure,the addition of corncobs at different temperatures reduced the diversities of the microbial community after digestion,but it had different effects on the microorganisms at the phylum level and the genus level.Adding corncobs at 35℃ increased the abundances of Proteobacteria and Paeniclostridium after digestion,and the abundance of Proteobacteria gradually increased from 1.12% to 7.85% with the increase of corncob content.Adding corncobs increased the abundance of Bacteroidetes and Hydrogenispora after digestion,and the abundance of Hydrogenispora gradually increased from 9.11% to 40.68% with the gradual increase of corncob content at 55℃.At 65℃ adding corncobs reduced the abundance of Psychrobacter after digestion,and affected phylum level microorganisms irregularly.(4)The RDA analysis showed that the physicochemical factors and microbial communities at the three temperatures affected the changes in the abundances of ARGs together.VFAs was the main physicochemical factor affecting the changes in ARGs at different temperatures.Network analysis showed that Proteobacteria was the key microorganisms at phylum level that affected the changes in ARGs.Psychrobacter and Pseudomonas in Proteobacteria were the main potential host bacteria that affected ARGs at 35℃,65℃ and 55℃,respectively.Corn cobs respectively affected the abundances of these microorganisms thus changing the abundance of ARGs at different temperatures.