Succession regulation of Lactobacillus phages and its effect on the active Lactobacillus structure during the radish Paocai fermentation

The physicochemical indexes, active microbial community structure, metabolic function, and correlation between virus groups and microbes of radish Paocai during the fermentation were studied by relevant national standard method, macrotranscriptome sequencing technology, Kyoto Encyclopedia of Genes and Genomes (KEGG) database, and Spearman correlation analysis. The results indicated that in the fermentation process of radish Paocai, the pH value increased slightly at the beginning of fermentation, the reducing sugar content decreased rapidly, the salt content showed a non-monotonic increasing trend, the total acid content increased first and then decreased, the malic acid and succinic acid were rapidly consumed, and the lactic acid and acetic acid became the main organic acids. The predominant active microflora underwent a gradual transition to Lactobacillus (7.91%-22.68%) with fermentation, with Lactobacillus pentosus, Lactobacillus parafarraginis, Lactobacillus plantarum and so on being the dominant species among the 62 species of Lactobacillus. The major metabolic pathways of the active microflora were metabolism and genetic information processing. Additionally, the pathway associated with the immune system was active during the initial fermentation phase. The main virus groups were Siphoviridae, Myoviridae and so on in the radish Paocai, among which Lactobacillus phage, especially LP65, ATCC8014-B2 and so on were extremely active during the initial fermentation phase. A total of 30 significant positive and 14 significant negative correlations between 6 Lactobacillus phages and 62 Lactobacillus were found (|r |>0.8, P<0.05). The results of this study laid a foundation for revealing the regulatory mechanism of virus groups on microflora in the radish Paocai system.