Dynamic Changes And Functional Analysis Of Bacteria During The Fermentation Of Da-jiang

Da-jiang is a traditional fermented food,and the fermentation of microorganisms is the key step in its production.The quality of da-jiang is directly affected by the consequent of microbial fermentation.At present,the research on the community composition and dynamic changes of microbes is still not comprehensive enough.The analysis of microbial function is rare.Therefore,it is necessary to used new techniques to understand the dynamic changes and its role of microorganisms in the fermentation of da-jiang.The samples of da-jiang collected from different fermentation periods were taken as the research objects.The metagenomics and bioinformatics analysis methods were used to analyze the community composition and dynamic changes of bacteria during the fermentation,and the functional genes of bacteria were annotated.We analyzed the metabolic pathways involved in the fermentation of bacteria,and further explain the specific role of bacteria in the fermentation from the perspective of functional annotation.The main results were as follows:(1)A total of 164134849 Raw reads were obtained by metagenomic sequencing.142306274 Clean reads were obtained by quality control,of which S1 was at most of50751180 and S5 was at least of 12947289.261326 contigs were generated by Metavelvet,with a maximum contig length of 36361 bp and an average contig length of 994 bp,the average contigs of each sample was 52265.The ORFs prediction of the assembly results indicates a total of 416505 ORFs were predicted,the percentage of complete ORFs was26.33%,the maximal length was 11598 bp,the average length was 603.9 bp,the length of the gene was mainly concentrated below 2000 bp.The gene diversity index showed a downward trend with the progress of fermentation.(2)A total of 14 phyla,248 genus,841 species were detected in the fermentation of da-jiang,the dominant bacteria were Leuconostoc mesenteroides,Leuconostoc citreum,Leuconostoc lactis,Lactococcus lactis,Acinetobacter lwoffii,Acinetobacter johnsonii,Enterobacter sp.638,Enterococcus faecium and Enterococcus faecalis.From the perspective of dynamic changes,the abundance of Leuconostoc mesenteroides decreased first and then increased,finally reached to 65%.The abundance of Acinetobacter lwoffii and Acinetobacter johnsonii remained unchanged at 30 days before the fermentation,and remained at 15%,but as the fermentation progressed,its abundance gradually decreased.Enterobacter sp.638,Pantoes vagans,Pseudomonas fluorescens,Lactococcus lactis and Lactococcus garvieae showed a decreasing trend,the abundance of Lactobacillus plantarum increased first and then decreased,Enterococcus faecium and Tetragenococcus Halophilic were gradually developed until the late stage of fermentation.(3)The functional genes of bacteria in the fermentation of da-jiang are mainly related to Carbohydrate metabolism,Amino acid metabolism,Membrane transport,Inorganic ion transport and metabolism,Energy metabolism,signal transduction,Metabolism of coenzyme and vitamins,Cell wall/membrane/envelope biogenesis,Replication,recombination and repair and Transcription.There are also a small number of genes involved in RNA processing and modification,extracellular structures,and gene resistance.(4)Analysis of related metabolic pathways shows that most of bacteria can participate in basic metabolism,such as carbohydrate metabolism and amino acid metabolism.A few species are related to the characteristics of da-jiang,such as Pseudomonas Chlororaphis secrete tyrosinase,which can oxidize tyrosine,this metabolism is closely related to the color of da-jiang.During the fermentation of da-jiang,arginase is mainly derived from four kinds of bacteria,and a variety of bacteria can secrete ornithine decarboxylase and spermidine synthase,which are involved in the metabolic of putrescine and spermine.Pseudomonas fluorescens secretes tyrosine decarboxylase and L-tryptophan decarboxylase,which are involved in the production of tyramine and histamine.A variety of bacteria can secrete lysine decarboxylase,which is involved in the production of cadaverine.