Characterisation of microbial succession and exploration of the stability maintenance strategy of phage community on microbes in radish paocai

Abstract

Previous research focused on the safety control of phages in food. In recent years, numerous phages have been extensively characterised in fermented foods, where they change along with fermentation process but do not compromise product quality. However, the potential roles of phages in fermented foods remain unclear. Microbial steady state is critical for maintaining normal radish paocai fermentation. To explore stability maintenance strategies for phages, their structure and interactions with microbes were investigated across two microbial structural systems during fermentation. Microbial counts showed the absence of fungi in the non-steady-state environment (NE), whereas high fungal levels (6.78 ± 0.09 log colony-forming units/mL) were detected in the steady-state environment (SE). Metagenomic analysis revealed that microbial structure remained stable in SE but changed markedly in NE. Pediococcus ethanolidurans and Lactococcus lactis were the species that differed significantly between SE and NE. Microbial succession exhibited a significant association with physicochemical environments in NE (P < 0.05), whereas microbial abundance fluctuations were unaffected by physicochemical stress in SE. Caudoviricetes was identified as the dominant viral class. Cluster analysis showed that NE systems displayed high variability with dramatic shifts across multiple viral genera (Clusters 3–6). In NE, 25 lytic and 226 lysogenic phages were identified, while 3 lytic and 29 lysogenic phages were found in SE. Phage host prediction indicated preferential targeting of harmful bacteria (e.g., Escherichia) in NE, contrasted with phage predation on fermentation-associated lactic acid bacteria in SE. Genomic analysis indicated that Lactiplantibacillus abundance and its corresponding phages remained stable in SE but increased sharply in NE on day 3. Lactiplantibacillus phages isolated from NE and SE displayed strict host specificity at the strain level and exhibited potent lytic activity across different fermented food matrices. This study advances our understanding of steady-state maintenance mechanisms in vegetable fermentation systems and offers new insight for cross-system phage applications.