Study On Community Structure And CO₂-fixing Characteristics Of Autotrophic CO₂-fixing Bacteria During Composting

In this paper,the effects of different C/N（10,25,40）and mixed electron donors（Na₂S,Na₂S₂O₃,NaNO₂）on physicochemical properties,abundance and diversity of autotrophic bacteria in cow manure-sugarcane leaves composting were studied.The composting with different C/N were conducted for 50 days to analyze the changes of physicochemical parameters during composting.Meanwhile,fluorescence quantitative PCR（qPCR）and high-throughput sequencing were performed with cbbL as the marker gene.The results showed that the high temperature duration of composting with C/N=25 and C/N=40were longer than that with C/N=10.The degradation rates of organic matter with C/N=10,C/N=25 and C/N=40 were 10.59%,12.72%and 16.74%respectively.The results of qPCR showed that the abundance of cbbL in three treatments increased gradually with composting.The maximum values of C/N=10,C/N=25and C/N=40 were 4.08×10⁹ copies·g^-1,1.23×10¹00 copies·g^-1 and 5.96×10⁹copies·g^-1,respectively.The results of high-throughput sequencing showed that the dominant phyla of cbbL-containing bacteria in three treatments were Proteobacteria and Actinobacteria.However,the difference of relative abundance of dominant genera among three treatments was obvious.In order to explore the influence of electron donors on the succession of autotrophic bacterial community during composting,1.25%Na₂S,0.5%Na₂S₂O₃ and 0.46%NaNO₂ were added to the composting as mixed electron donors.The effects of electron donors on physicochemical parameters,characteristics of dissolved organic matter（DOM）and characteristics of humic substance（HS）were also studied.The results showed that the degradation rate of organic matter（OM）in experimental group was 14.6%,which was significantly higher than that in control group（11.5%）.Adding electron donors effectively promoted the degradation of OM and reduced the loss of ammonia nitrogen.In addition,the results of lignocellulose content showed that the addition of electron donors promoted the degradation of hemicellulose,but did not promote the degradation of cellulose and lignin.Ultraviolet-visible spectroscopic data showed that the addition of mixed electron donors accelerated the decomposition and transformation of substances in composting,and enhanced the aromatization of DOM and HS.The results of high-throughput sequencing showed that Proteobacteria and Actinobacteria were the main phyla of two composting systems.With the progress of composting,the community of cbbL-containing bacteria changed significantly at genus level.The dominant genera in control group were Xanthobacter,Sinorhizobium,Thiobacillus and Mesorhizobium,while the dominant genera in experimental group were Sinorhizobium,Rhodobacter,Thiobacillus and Methylococcus.The mixed electron donors altered the structure of chemoautotrophic bacterial community by inhibiting the occurrence of genera of Xanthobacter and Mesorhizobium and inducing the growth of genera of Rhodobacter and Methylococcus.Alpha diversity analysis showed that the addition of mixed electron donors improved the richness and diversity of cbbL-containing bacteria during thermophilic period of composting.Redundancy analysis（RDA）showed that OM and moisture were the major environmental factors affecting the succession of cbbL-containing bacterial communities.