Metatranscriptome Analysis Of Microbial Structure And Its Metabolic Function During Natural Fermentation Of Soybean Paste

Soybean paste is a traditional fermented product with unique flavor and natural fermentation of soybean.The structure of the microbial community structure directly affects the quality of the soybean paste.At present,the research on the structure and function of the flora in the fermentation process of soybean paste is mostly concentrated on the DNA level.The results do not reflect the true situation of the flora in the soybean paste.The actual metabolic reaction during the fermentation process can only be speculated.Therefore,in order to reflect the true situation of microbial community structure of natural fermented soybean paste and avoid the interference of dead bacteria caused by traditional molecular biology methods,try to use metatranscriptome technology to analyze the living microbial community in the soybean paste fermentation system.This study deeply analyzes the functional gene expression changes of microbes in different fermentation stages and the adaptive response of microorganisms to the environment.From the functional abundance spectrum and the species composition spectrum,the differences were compared.The amount of differential expression during the fermentation period,and the integration of important physical and chemical indicators with the results of metatranscriptome,while using Solidphase Micro-Extraction(HS-SPME)and GC-MS.The analysis of volatile flavor components of traditional soybean paste,together with the metatranscriptome,revealed the species and related functional groups that play a leading role in the fermentation process of soybean paste.1.Firstly,a comparative study on the pretreatment methods of total RNA extraction from soybean paste was carried out.The centrifugation of the soybean paste sample can well solve the effect of complex fermentation system for RNA extraction.This sample pretreatment method was especially helpful for the total RNA extraction of soybean paste in the early stage of fermentation.2.Metatranscriptome function study results showed that although each database has its own emphasis,it is a large number of annotations to metabolic activities,indicating that the microbial activities in natural fermented soybean paste were mostly related to amino acids,carbohydrates and energy metabolism.Metatranscriptome species annotation results show that bacteria actually play a leading role in the fermentation stage of liquid sauce.Its main genus was Tetragenococcus,Lactobacillus,Staphylococcus,Oceanobacillus and Enterococcus,and fungi only have a certain abundance in the early stage of fermentation.Most species were positively correlated,but Lactobacillus was negatively correlated with thespecies of the Sporosarcina,Aspergillus,Aspergillus and Oceanobacillus.Sample function and species level consistency were high in each fermentation stage.3.The results of RDA analysis showed that there was a positive correlation between p H and water and a negative correlation with salt concentration.Most of the genus were positively correlated,and Lactobacillus was strongly negatively correlated with Oceanobacillus.In addition,Staphylococcus,Enterococcus,Bacillus,Virgibacillus,Aspergillus and Rhizopus were positively correlated with p H and water.Tetragenococcus,Oceanobacillus,and Kurthia were negatively correlated with p H.There was a positive correlation between Lactobacillus and Tetragenococcus and chromaticity,indicating that it may have some influence on the color change of soybean paste.Only Lactobacillus was positively correlated with salt concentration.4.A total of 27 volatile components were detected.The most important volatile component being esters.Correlation analysis showed that Enterococcus,Tetragenococcus and Lactobacillus may be the main functional bacteria of lipid metabolism.Tetragenococcus halophilus,Lactobacillus rennini,Lactobacillus acidipiscis,Lactobacillus plantarum,Enterococcus faecalis,Bacillus subtilis,and Aspergillus flavus have a significant positive correlation with flavor substances,which may be core microbial species that have an important influence on the synthesis of volatile flavor substances.