Isolation and characterization of bacteria that produce quorum sensing molecules during the fermentation and deterioration of pickles

Pickles are typical traditional Chinese fermented vegetables. Complex microbiota interacts throughout the fermentation and deterioration process. Minimal studies are available involving quorum sensing (QS) signaling in pickles. This study investigated the changes in the general pickle properties and microbial diversity at 4 d, 31 d, and 79 d. The QS signaling activity of various strains isolated at these key time points was screened using biosensor strains, while the types of signal molecules were further identified using UHPLC/QTOF-MS/MS. At 4 d, Lactobacillus represented the dominant genus, while Lactobacillus plantarum was identified as the bacteria with AI-2-producing ability. At 31 d, the dominant genus was also Lactobacillus, while the relative abundance of Pediococcus displayed a distinct increase. At this time point, L. plantarum represented the AI-2-producing bacteria, followed by Lactobacillus brevis, Pediococcus sp., Enterobacter sp., and Bacillus megaterium. At 79 d, Lactobacillus was displaced by Enterobacter as the dominant microorganisms, while the AI-2-producing bacteria were identified as L. plantarum, Enterobacter sp., B. megaterium, Klebsiella sp., and Staphylococcus sp. Moreover, AHL activity was only present in isolates from the 79-d brine and was identified as C4-HSL and C6-HSL. In addition, the luxS gene was amplified via cDNA reversely transcription from the total RNA extracted from the brine at all three time points using the L. plantarum luxS primers. The AHL-related genes were only amplified in the RNA of 79-d brine samples using Klebsiella pneumoniae- and Bacillus cereus-related primers. This study presented theoretical references for QS during pickle fermentation and deterioration.