Phylogenetic Characterization Of Rural Household Biogas Digesters And Its Substrate Microbial Community By 16S-rDNA Sequences Analysis In Gansu

Aims and methods: Human demand for energy is growing, but traditional fossil energy is rapidly reduced, biogas technology is an effective way for China to cope with the problem of rural energy crisis and environmental pollution. Methanogenesis from the biomass in the anoxic biogas reactors is catalyzed bysyntrophic cooperation between anaerobic bacteria, syntrophic acetogenic bacteriaand methanogenic archaea. The lack of knowledge of microbial community structure directly impede the process improvements. However, understanding of microbial community composition withinthe biogas reactors may improve the methane production from biomass fermentation. The research mostly focused onthe mesophilic digesters methanogens diversity. However, research on microbial diversity of rural biogas digesters under normal temperature of Gansu is rare.In this study the microbial communities in the rural household biogas digesters treating pig or cattle manure were investigated for their phylogenetic compositionby amplified ribosomal DNA restriction analysis and sequencing of 16S-rDNA genes.Results and conclusions:1. Reveal the microbial diversity and community structure of the mesophilic and low temperature rural household biogas digesters. A total of 353 bacterial groups (14 phylum) and 20 archaea groups (6 genera) were obtained. The dominant phylotypes were affiliated to Methanomicrobiales (archaea) and Firmicutes, Bacteroides, Proteobacteria (bacteria). The results show that high diversities of microbial composition and metabolism in the rural household biogas fermentation system, and bacterial diversity was higher than archaea. The results of Jaccard index(bacteria:0.15-0.31, the archaea:0.01-0.50) and PCA indicate that digesters microbial community structure and diversity having significant differences.2. There are significant differences in dominant methanogenic microbial community of different digesters. The abundance of Methanocorpusculum and Methanogenium was significantly higher in low-temperature digesters than mesophilic digesters, and the abundance of Methanoplanus was significantly higher in mesophilic digesters than low-temperatures’. Methanocorpusculum as absolute advantage community in digesters treating pig manure, but the distribution of dominant groups is more uniform in digesters treating cattle manure.3. The most methanogens were typical hydrogenotrophic in digesters. Therein the hydrogenotrophic methanogenesis seems to be the major pathway of methane formation.4. Understanding the interaction of functional groups in rural household digesters. Firmicutes, Bacteroides hydrolyzes and ferments complex polymeric substances mainly lipids, cellulose and protein. Proteobacteria, Synergistetes ferments glucose and amino acids to fatty acids, acetate and hydrogen. Methanomicrobiales converts acetate and hydrogen to methane and carbon dioxide.5. Reveal the microbial diversity and community structure of pig and cattle manure. A total of 290 bacterial groups (11 phylum) and 13 archaea groups (5 genera) were obtained. The dominant phylotypes were affiliated to Methanomicrobiales (archaea) and Firmicutes, Bacteroides, Proteobacteria (bacteria). The results show that a rich microbial species diversity of bacteria than archaea, pig manure than cow dung. The results of Jaccard index(bacteria:0.12-0.24, the archaea: 0.33-0.55) and PCA indicate that there are significant differences in microbial community structure and diversity of fecal material.6. Based on phylogenetic analysis, results show some groups showed the same seasonal differences in pig and cattle feces. The abundance of winter samples than in summer samples including β-,γ-,δ-,ε-Proteobacteria, Verrucomicrobia and Chloroflexi, and the summer samples than in winter including Firmicutes, Bacteroidetes, Lentisphaerae and Tenericutes.7. Revealing the correlation of microbial structure which digesters and its raw material. First, the digesters and feces both had similar community structure. Second, they showed the opposite trend in the abundance of the bacterial community Firmicutes, Bacteroides, Proteobacteria. Third, the absolutely dominant groups in feces was Firmicutes which degradation of cellulose, however, in digesters Proteobacteria abundance increased significantly.8. Rural household biogas digesters treating manure have unique fermentation characteristics. High pH(7.92-8.26), unstable temperature(30-40℃), extended HRT(70-90 days), eventually leading to the gas unstable gas production decreased phenomenon.Significance and Impact: This study not only gave a first insight of the overall microbial structure in mesophilic and low-temperature rural biogas digesters which manure as substrate, revealing the correlation of microbial structure which digesters and its raw material, preliminary analysis of the interaction of methane fermentation main function flora; but also for the promotion and efficient operation of rural household biogas fermentation provide sometheoretical basis.