Divergent role of abiotic factors in shaping microbial community assembly of paocai brine during aging process.

Microbial communities in fermented food are shaped by a myriad of abiotic factors. The respective roles of abiotic factors in shaping the dynamic bacterial community of paocai during aging remain unclear. In the present study, 100 paocai samples (pH: 2.95-5.23; NaCl content: 0.13-15.41%; total acid: 6.61-18.33 mg/mL; total sugars: 7.96-487.90 μg/mL; total viable count: 3.55-8.99 LogCFU/mL; aging time: 5 day-15 year) were analyzed through high-throughput sequencing and the results revealed five dominant bacterial genera across different samples, including Lactobacillus, Pediococcus, Leuconostoc, Lactococcus and unclassified genera. Both NaCl and total acid (TA) were the major factors regulating bacterial community divergence in paocai. Based on these results, the microbial communities were reconstructed by manipulating the TA and NaCl contents in vitro to validate the effectiveness of these factors in shaping microbial communities during paocai fermentation. Results showed that roles of abiotic factors differentiated during fermentation. At the early stage, salt was the first abiotic filter, mainly working through promoting the abundance of Lactococcus and Leuconostoc. As the TA content increased, the selective role of salt weakened while acid became the dominant at the later stage, as evidenced by the increased abundance of Lactobacillus and Pediococcus following the increase of TA content.