Microbial Metagenomic Study Of Puer Tea During Pile-fermentation

Up to now, there is no report about the taxonomic and functional analysis of microbial communities in fermenting puer tea by metagenomic approach. In this study, metagenomic method was first used in puer tea using massively parallel pyrosequencing the total community DNA of the fermenting microbes involved in puer tea to delineated a relative comprehensive overview of microbial taxonomic while also preliminary characterzing the functional ontologies of microbial genes present in puer tea pile-fermentation.At first, combining with the actual situation of puer tea fermentation microbial community, we developed a method of extraction microbial total DNA of puer tea which result of the DNA has a well integrity, OD260/OD280=1.8-1.9, and OD260/OD230>1.6. The sample at day25of the fermentation process has been chosen for pyrosequencing which characteristics were as follows:after fermentation for25days while the tea pile was turned the3rd time, the core temperature of the pile reached up to64℃, with the pH at5.1, the water content at232.4g kg-1, and the polyphenols content at146.1g kg-1. A total of251,738pyrosequencing reads (9197contigs and145402singletons) were generated from pyrosequencing. The taxonomic analysis revealed three dominant bacterial phyla:actinobacteria (30.08%), proteobacteria (24.47%),. and firmicutes (20.23%); and one dominant eukaryotic phylum:ascomycota (15.21%); The proportion of yeast far outweigh the mould. The puer tea metagenomic revealed higher proportions in "carbohydrate metabolism""stress response" compared to8publicly available other environmental metagenomics. Moreover, two categories,"metabolism of terpenoids and polyketides" and "biosynthesis of other secondary metabolites" were selective analysis and presented69enzymes in16pathways. A total of15kinds of common foodborne bacterial pathogens were identified in fermenting puer tea. Salmonella sp was of the highest percentage (1.74%), while the other opportunistic foodborne pathogens were in lower abundance (<1%).2.42%reads from our metagenomic pyrosequencing could be mapped to virulence, disease and defense genes and61function genes in12pathogenic disease infectious pathways presented in this study.These results preliminary delineated the taxonomic and functional profiles of the microbial community of puer tea, but further studies, such as metatranscriptomic and the metabolomic, are also needed to determine the microbial metabolic processes more accordant with the practical situation. The pathogens, virulence genes and pathogenic disease infectious pathways involved in the process of puer tea fermentation warning us that we should pay more attention to the environmental health of the puer tea production, upgrade the equipment, and standardize the manufacturing practice to accommodate the requirements of modernization and globalization of puer tea production.