Correlation Of Chemical Change And Microbial Community Succession During Microbial Fermentation Of Fuzhuan Brick Tea

Fuzhuan brick tea is a dark tea which is processed by a unique microbial fermentation process.The chemical change and the unique flavor during this process are caused by both bacteria and fungi.So far,no report has been documented with regard to the correlation between bacterial and fungal community,or that between succession of microbial community and chemical changes of Fuzhuan brick tea.In this study,amplicon sequencing and metabonomics were integrated to explore these correlations.Molecular network analysis which based on LC-MS proved that metabolite X was a metabolite of Eurotium cristatum.The chemical change during microbial fermentation process of Fuzhuan brick tea were mainly divided into two groups which correlated to fermentation times of 1-7 days and 8-21 days.And it was found that metabolites X,phosphatidylcholine derivatives,mono flavan-3-ol oxidation products,purine alkaloids,amino acid derivatives,oligosaccharides and pyrimidine derivatives were the key chemical composition between the two groups.What's more,the content of the former four chemical composition in fermentation times of 1-7 days were less than the content of them in fermentation times of 8-21 days,but the content of the latter three chemical composition were opposite.The fungal community obtained 3 phyla,14 classes,35 orders,67 families and 92 genera.Cluster analysis which based on the abundance of fungi and the unifrac distance found that the succession of the fungal community during microbial fermentation process of Fuzhuan brick tea were clearly divided into two stages which correlated to the fermentation times of 1-4 days and 5-21 days.It was found that the significantly different genera between the two stages were Eurotium,Debaryomyces,Cyberlindnera,Penicillium,Candida,Rhizomucor and Aspergillus.Besides,only the abundance of Eurotium increased from the fermentation times of 5 days,but others were reduced.In fact,the phenomenon which Eurotium is the dominant genus during the middle and the later stage of microbial fermentation process verified this result.The bacterial community obtained 42 phyla,83 classes,169 orders,311 families and658 genera.Unlike the fungal community,cluster analysis found that the bacterial community of Fuzhuan brick tea showed complex changes which did not show a regular linear change with the increase of fermentation days during the microbial fermentation process.The bacterial structure which correlated to fermentation times of 1-2 days and4-5 days were similar,and the bacterial structure which correlated to fermentation times of 3 days,6-9 days,12-15 days and 20-21 days were similar,and the bacterial structure which correlated to fermentation times of 10-11 days and16 days were similar.The statistical analysis of significantly different genus found that the grouping results were resulted from the changes of 119 genera in the bacterial community.The abundance of metabolite X and Eurotium emerged the same rising trend,but the rising time was significantly different.We speculate that the process which Eurotium produce metabolite X was effected by the bacterial community of Fuzhuan brick tea.Based on the grouping results of the chemical composition,we forcibly analyzed the bacterial community and counted the significantly different genera.It was found 99 significantly different genera such as Meiothermus,Paenibacillus,Nocardiopsis,Bacillus,Thermus and so on.Besides,we got 25 important genera which screened by VIP.Through pearson correlation analysis,it was found that there was a positive correlation between the eight genera which were Paenibacillus,Bacillus,Thermus and so on with the four significantly different chemcial composition which were metabolite X,phosphatidylcholine derivatives and so on.It was possible that the eight genera promoted Eurotium to transform the chemical environment of Fuzhuan brick tea,and eventually formed a special flavor of Fuzhaun brick tea.Through pearson correlation analysis between the key bacterial genera and the key fungal genera,it was found that there was a positive correlation between the bacteria which were Cohnella,Meiothermus,Paenibacillus,Nocardiopsis,Bacillus,Thermus with Eurotium.These results hint that there was a symbiotic relationship between these bacteria and Eurotium.These results prove that the chemical change of Fuzhuan brick tea was greatly influenced by the interaction of the bacterial community and the fungal community.And our experiment do the preliminary study for exploring the mechanism how Fuzhuan brick tea and even other fermented food form the unique flavor and quality.