Abstract: The effect of the luxS gene on the NaCl tolerance of Lactobacillus plantarum wild-type strain KLDS1.0391 was investigated by comparing it with its luxS deletion mutant strain. Meanwhile, the influence of the luxS gene on the growth rate and bacteriocin synthesis of this strain under various concentrations of NaCl stress (0%, 2%, 3%, 4% and 6%) were measured. The expression levels of genes related to bacteriocin biosynthesis were determined by real time quantitative PCR technique at the transcriptional level. The results showed that the survival rates of the two strains decreased gradually with the increase of NaCl concentration. The tolerance to NaCl concentrations over 3% of the wild type strain was significantly stronger than that of its mutant (P < 0.05) at the same condition. Moreover, the growth rate and bacteriocin synthesis of the mutant were significantly lower than those of the wild-type strain (P < 0.05) at each NaCl concentration. Real time quantitative PCR showed that the expression of the bacteriocin structure gene plnEF and the double regulator genes plnD and plNC8HK were all significantly down-regulated (P < 0.05) when the mutant was cultured to the stationary phase for 24 h. Therefore, luxS gene deletion significantly reduced the NaCl tolerance of L. plantarum KLDS1.0391. Meanwhile, its growth rate and bacteriocin synthesis ability under NaCl stress decreased significantly due to deletion of the luxS gene.

Key words: Lactobacillus plantarum, luxS, NaCl stress, bacteriocin, gene expression