Effects of buffer salts on the freeze-drying survival rate of Lactobacillus plantarum LIP-1 based on transcriptome and proteome analyses

Buffer salts are often added to culture medium to promote bacterial growth. However, we found that buffer salts can improve the freeze-drying survival rate. In this experiment, the mechanisms for the effects of different buffer salts on the survival rate of freeze-dried strains were examined. The results showed that buffer salts had important effects on the freeze-drying survival rate of L. plantarum LIP-1 that were related to changes in fatty acid composition. Different buffer salts affected the expression of fatty acid metabolic genes. A new gene cluster that regulates fatty acid metabolism and synthesis was discovered. Potassium ions in buffer salts upregulated the trkA gene and lysR-type transcription factor, and then upregulated the expression of fatty acid synthesis-related acc and fab family genes. These genes help to extend the fatty acid carbon chain and promote the unsaturated fatty acids content, which improves cell membrane fluidity and improves resistance to freeze-drying.