ABSTRACT
The microbiome in fermentation has direct impacts on the quality of fermented foods and is of great scientific and commercial interest. Despite considerable effort to explain the microbial metabolism associated with food fermentation, the role of the microbiome in pu-erh tea fermentation remains unknown. Here, we applied integrated meta-omics approaches to characterize the microbiome in two repeated fermentations of pu-erh tea. Metabarcoding analysis of bacterial 16S rRNA genes showed a decrease in the proportion of Proteobacteria and an increase in the abundance of Firmicutes during fermentation. Metabarcoding analysis of fungal internal transcribed spacer (ITS) sequence demonstrated that Rasamsonia, Thermomyces, and Aspergillus were dominant at the intermediate stage, whereas Aspergillus was dominant at other stages in fermentation. Metaproteomics analysis assigned primary microbial metabolic activity to metabolism and identified microbial carbohydrate-active enzymes involved in the degradation of polysaccharides including cellulose, xylan, xyloglucan, pectin, starch, lignin, galactomannan, and chitin. Metabolomics and high-performance liquid chromatography analysis revealed that levels of phenolic compounds, including gallates, decreased whereas contents of gallic acid and ellagic acid significantly increased after fermentation (P < 0.05). The changes in levels of gallates and gallic acid were associated with the hydrolysis of tannase. Glycoside hydrolases, phenol 2-monooxygenase, salicylaldehyde dehydrogenase, salicylate 1-monooxygenase, catechol O-methyltransferase, catechol dioxygenase, and quercetin 2,3-dioxygenases were hypothesized to be related to oxidation, conversion, or degradation of phenolic compounds. We demonstrated microbiota in fermentation and their function in the production of enzymes related to the degradation of polysaccharides, and metabolism of phenolic compounds, resulting in changes in metabolite contents and the quality of pu-erh tea.IMPORTANCE Fermented foods play important roles in diets worldwide and account for approximately one-third of all foods and beverages consumed. To date, traditional fermentation has used spontaneous fermentation. The microbiome in fermentation has direct impacts on the quality and safety of fermented foods and contributes to the preservation of traditional methods. Here, we used an integrated meta-omics approach to study the microbiome in the fermentation of pu-erh tea, which is a well-known Chinese fermented food with a special flavor and healthful benefits. This study advanced the knowledge of microbiota, metabolites, and enzymes in the fermentation of pu-erh tea. These novel insights shed light onto the complex microbiome in pu-erh fermentation and highlight the power of integrated meta-omics approaches in understanding the microbiome in food fermentation ecosystems.
ABSTRACT
BACKGROUND: MicroRNAs are a class of highly conserved, small, noncoding RNAs that tailor gene expression mainly at the posttranscriptional level. The aim of the present study was to investigate the renal expression profiles of microRNAs and their potential involvement in early diabetic nephropathy. METHODS: Diabetic models were induced with streptozotocin in DBA/2 mice. MicroRNAs were detected by microarray and subjected to bioinformatics analyses. Real-time PCR and Western blots were performed. The relationships between pathological changes and microRNA expression were evaluated by linear regression analysis. Apoptosis and proliferation of cultured mesangial cells treated with microRNA inhibitor were determined by flow cytometry and MTT assay, respectively. RESULTS: Nine microRNAs, including miR-1187, miR-320, miR-214, miR-34a, miR-762, miR-466f, miR-720, miR-744 and miR-1937b, were increased significantly. Another 9 microRNAs, including miR-1907, miR-195, miR-568, miR-26b, miR-703, miR-1196, miR-194, miR-805 and miR-192, were decreased remarkably in diabetic mice. The levels of microRNA repressing BCL2 decreased. Accordingly, BCL2 levels were found elevated and caspase-3 and caspase-8 levels decreased in the diabetic group. MicroRNA-195 expression was negatively related to glomeruli diameter, mesangial score and extracellular matrix (ECM) accumulation. Moreover, the microRNA-195 inhibitor protected mesangial cells from apoptosis and promoted the cellular proliferation in vitro. CONCLUSIONS: These results demonstrated that the abated microRNA-195 expression protected mesangial cells from apoptosis, suggesting that the antiapoptosis in a microRNA-regulated manner may play an important role in the early stages of diabetic nephropathy.