Study on the K⁺-dependent adaptability and transcriptomics of Vibrio parahaemolyticus under low-salt stress

Vibrio parahaemolyticus (V. parahaemolyticus) gradually shows significant adaptability to low - salt stress (0.25% NaCl), but its potassium ion (K⁺) - dependent mechanism remains unclear. This study systematically elucidated the stress resistance characteristics of V. parahaemolyticus in response to low-salt freshwater conditions mediated by K⁺. Through phenotypic analysis of multiple strains, it was found that when the K⁺ concentration was 0.1-0.4%, it was found that supplementation with 0.1-0.4% KCl restored bacterial growth kinetics in a concentration-dependent manner, with μmax increasing by 8.33% - 500.85% and Lag Time (LT) reduced by 26% - 84%. Moreover, K⁺ enhanced motility and markedly promoted biofilm formation within 48 h, resulting in a 1.5-8.7-fold increase in biofilm biomass. Transcriptome sequencing revealed that there were 614 DEGs under the condition of 0.4% KCl, such as iscS, galT, rplB, rpsC, rpsO, fliC, and qseB. This indicates that K⁺ mediates the restart of the core system of cellular substance and energy metabolism, while enhancing motility, group cooperation, and potential virulence. Ultimately, it helps the strain resume proliferation and adapt to stress in a low - salt environment. Although the colonization of Lateolabrax japonicus was still independent of salinity, K⁺ enhanced the pathogenicity in the intestinal model, increasing the inhibitory effect on Caco - 2 cells by 1.3-1.7 times. These findings establish K⁺ as a key coordinator for growth adaptability, metabolic recovery, and pathogenic expression, providing potential targets for reducing the risk of V. parahaemolyticus in the freshwater supply chain.