Abstract: The present study compared the heat, acid and bile resistance of biofilm and planktonic cells of L-ZS9 by colony counting method. The results showed that biofilm cells had stronger stress resistance than their planktonic counterpart. The transcriptional levels of the stress resistance-related genes atpβ, atpε, clp, pspC and ccpA and the luxS gene encoding the quorum sensing signal autoinducer 2 (AI-2) synthase were investigated in biofilm and planktonic cells through real-time PCR. The results showed that the transcriptional levels of these genes were up-regulated in biofilm cells compared to planktonic cells. AI-2 activity were measured by its ability to induce luminescence in the reporter strain Vibrio harveyi BB170 and the results showed that the supernatant of biofilm cells had higher AI-2 activity than planktonic cells. Exogenous AI-2 could regulate the transcriptional levels of the atpβ, atpε, clp, ccpA and luxS genes. This study suggested that biofilm protected the cells by physical defense and biofilm cells differed from planktonic cells in terms of the transcriptional levels of the investigated genes. The quorum sensing system played an important role in the formation and regulation of biofilm. This work has laid a foundation for producing functional foods based on biofilm probiotics with high activity.

Key words: Lactobacillus paraplantarum L-ZS9, biofilm, stress resistance, signal AI-2, transcription