From Diversity to Dominance: How Salt and CO₂ Shape LAB-dominated Ecosystems in Vegetable Fermentations

Research on microbial ecosystems is often challenging due to high diversity of microbial taxa present and the complexity of controlling environmental variables. To address these challenges, fermented foods are simpler and more reproducible model ecosystems, where both community composition and environmental factors can be more precisely controlled and manipulated. In this study, we focused on fermented vegetables which are typically dominated by lactic acid bacteria (LAB). It is not completely understood why lactic acid bacteria (LAB) consistently drive the spontaneous fermentation of vegetables such as cabbage and carrots and how variables such as vegetable substrates, salt addition, and carbon dioxide levels can impact microbial community dynamics. Here, we explored the temporal microbial dynamics in standardized fermentations of 11 different vegetables (including beetroot, bell pepper, cabbage, carrot, cucumber, fennel, green asparagus, leek, parsnip, sunroot, and tomato), revealing a consistent dominance of Leuconostoc and other LAB. Additionally, we investigated the impact of varying salt concentrations, demonstrating that lower salt levels resulted in a delayed appearance of the typically dominant LAB community, while simultaneously revealing a higher abundance of Weissella and various Enterobacterales taxa. These effects imposed by reduced salt concentrations were mitigated by CO2 injection, which reverted the enhanced Enterobacterales levels and increased the overall abundance of Lactobacillales. This study demonstrates how targeted manipulation of environmental parameters, such as salinity and gas composition, can be used to uncover ecological principles governing microbial succession and community assembly in reproducible fermentation-based model ecosystems.