Abstract: Lactobacillus paracasei SMN-LBK, which was isolated from traditional Koumiss in Tacheng, Xinjiang was subjected to ethanol stress at concentrations of 4%, 6%, 8% and 10%. The corresponding survival rates were 25.84%, 18.39%, 10.86% and 1.67%, respectively. A transcriptomic analysis was carried out on strain SMN-LBK under 10% ethanol stress to study the expression levels of differentially expressed genes at the transcriptional level. The results showed that a total of 50 genes were significantly down-regulated under 10% ethanol stress, including 1 gene involved in alanine, aspartate and glutamate metabolism, 2 genes involved in fatty acid biosynthesis, 8 ATP-binding cassette transporter genes, 3 genes involved in the phosphotransferase system (PTS), and 36 hypothetical protein genes. A total of 28 genes were significantly up-regulated, including 4 genes involved in alanine, aspartate and glutamate metabolism and 24 hypothetical protein genes. Six differentially expressed genes were selected for real-time quantitative polymerase chain reaction (real-time PCR) to verify the transcriptome results, and it turned out that the two methods gave consistent expression levels. These genes are related to the biosynthesis of the main cell wall components peptidoglycans and teichoic acid, which are capable of protecting themselves from damage caused by ethanol stress by increasing the expression of these genes. These genes may be closely related to the ethanol stress mechanism of L. paracasei SMN-LBK. This study lays the foundation for further elucidation of the stress-tolerance mechanism of Lactobacillus.

Key words: Lactobacillus paracasei, ethanol stress, transcriptomics, real-time fluorescence quantitative polymerase chain reaction