Adaptive laboratory evolution and mechanisms of salt tolerance in Lactiplantibacillus plantarum

Lactiplantibacillus plantarum is known to be widely accepted as starter culture with antibacterial and biogenic amines (BAs) degrading abilities, but its salt tolerance is a crucial factor limiting its effectiveness as a starter for fermentation. In the present study, the adaptive laboratory evolution (ALE) approach was used to enhance the salt tolerance of the parental strain Lpb. plantarum His6-WS. Sixteen salt-tolerant strains were obtained by selection on MRS medium containing 10% NaCl. Compared to the parental strain, the evolved strain Lpb. plantarum H11-ES exhibited excellent genetic stability, a shorter lag period and a higher maximum population density in the MRS containing 8% NaCl. Additionally, the evolved strain Lpb. plantarum H11-ES improved its BAs-degrading ability in high-concentration NaCl environments. Characterization of cell morphology showed that the evolved strain Lpb. plantarum H11-ES had significantly strengthened the integrity and length of cell membrane and cell wall compared to its parent. Furthermore, whole genome resequencing revealed that the mutations in the poly(glycerol-phosphate) alpha-glucosyltransferase (TagE) and the ATP-binding cassette (ABC) transporters likely contributed to the evolution of salt-tolerant by altering cell morphology and participating in membrane transport. Collectively, this study successfully isolated Lpb. plantarum strain with enhanced salt tolerance and amine-degrading abilities, while also highlighting the importance of the cell wall in increasing the salt tolerance. This provides a theoretical basis for future regulation and selection of salt-tolerant LAB.