Spatio-temporal Dynamics Of Prokaryotic Communities In The Biogas Digester Ecosystems In Yunnan

Biomass can biologically be converted to biogas using anaerobic digestion process with potential to reduce the carbon dioxide emission. In rural areas, the development of household biogas digesters can improve the energy utilization, governance the agricultural nonpoint source pollution and promote the virtuous cycle of ecological agriculture. Moreover, due to the complex microbial characteristics within the anaerobic digestion process, various reactor designs, operating conditions, and fermentation substrates would result in the variety of the microbial populations present in the ecosystem. Therefore, understanding the ecology and function of the microbial community was critical to improve the conversion efficiency in the anaerobic digestion. But there were little reports about the microbial community structure in the rural household biogas fermentation ecosystem in Yunnan.There are a rich geographical and climatic diversity and large numbers of household biogas digesters in Yunnan. But there are still many problems in the management and use of household biogas digesters, such as unstable gas production, less gas production, winter off phenomenon. Also there were rarely the studies about the microbial diversity in this ecosystem in Yunnan. Therefore, it would be a creative work to study the ecological and spatial distribution of the microbia in the household biogas digesters from the different climatic types and geographic regions in Yunnan. In addition, exploration the dynamic changes of microbial community in a thermostatic batch-lab biogas digester was also a challenging work.The ecological and functional distributions of prokaryotic communities were investigated in the rural household biogas digesters from different climatic types and geographic regions in Yunnan. It was systematically analyzed the community structures using Illumina high-throughput sequencing technology. The results demonstrated that there is a difference of microbial community spatially distributed in different climatic regions. The second work was to study the dynamic changes of microbial community during a biogas digester process by applying the DGGE fingerprint and Illumina high-throughput sequencing. The changes of microbial community structures were investigated in the biogas fermentation process. The following results were obtained.Total of 21 rural household digesters were collected from four different climatic types and geographic regions in Yunnan. DNA extraction, sequencing and characterization of 10 typical rural digesters were performed. After sequencing, these samples totally generated 650,325 reads by the Illumina MiSeq sequencing. The RDP classifier analysis showed that all sequences were identified to 16 phyla and 5 Candidates phyla. These phyla were Crenarchaeota, Euryarchaeota, Acidobacteria, Actinobacteria, Bacteroidetes, Chlorobi, Chloroflexi, Fibrobacteres, Firmicutes, Gemmatimonadetes, Proteobacteria, Spirochaetes, Synergistetes, Thermotogae, Verrucomicrobia, Caldithrix. The most relative abundance populations were Firmicutes, Euryarchaeota and Bacteroidetes.The prokaryotic communities demonstrated high species diversity and significant biogeographic patterns in the rural biogas digesters from different climatic regions. These phyla of Firmicutes, Euryarchaeota, Bacteroidetes, Spirochaetes and Proteobacteria were predominated. But the characteristics of community compositions were distinct in these household biogas digesters from different climatic regions. The relative abundance of the phylum Firmicutes, in particular Clostridium, was the highest in XGP2 and XGP3 digesters (54.6% and 41.1%) with the lower temperature than other, but in contrast the phylum Euryarchaeota (particularly the genus Methanosaeta) was lowest abundance in two digesters. Furthermore, Bacteroidetes also had the different distributions in different climatic regions.The DGGE fingerprint showed that there were a high bacterial and archaeal abundance and diversity in the thermostatic batch-lab biogas digester at 21℃, which simulated the natural environments of the biogas digesters in the tropical climatic region of Yunnan. Cluster analysis revealed that the bacterial and archaeal communities were always changing in the processes. The result indicated that the changes of prokaryotes could be divided into three stages, but the time of bacteria was earlier than archaea.There were 17 digester samples were collected from the thermostatic batch-lab biogas digester during the biogas fermentation processes. Based on the Illumina MiSeq sequencing and RDP classifier analysis, these sequences were classified to 19 main phyla:Crenarchaeota、Euryarchaeota、Firmicutes、Bacteroidetes Proteobacteria、Spirochaetes、Chloroflexi、Synergistetes、Acidobacteria Actinobacteria、Fibrobacteres、Chlorobi、Verrucomicrobia、Armatimonadetes、 Caldithrix、Lentisphaerae、Thermotogae、OP9、OP11. Obviously, the Euryarchaeota、 Firmicutes、Bacteroidetes、Proteobacteria also were dominant groups in the thermostatic batch-lab biogas digester.Comparing with DGGE result, the dynamic changes of prokaryotes were also divided into three stages. The abundance of Euryarchaeota increased during the fermentation processes, range from 32.4% to 60.5%. The proportion of Firmicutes gradually reduced, from 19.2% to 6.4%. Bacteroidetes was also the same situation with Firmicutes, decreased from 15.7% to 5.9%.The redundancy analysis (RDA) indicated that the distribution of the prokaryotic communities was mainly affected by the total solid (TS) and fermentation temperatures in the different climatic regions. The RDA result demonstrated that the total solid (TS) and chemical oxygen demand (COD) were mainly factors effected on the trendance of bacteria; but the archaea were little affected by environmental factors in the thermostatic conditions.