Effects of L-cysteine on the freeze-drying survival rate of Lactiplantibacillus plantarum LIP-1

Amino acids are often used as probiotic growth factors. Their addition to the growth medium is found to effectively enhance the resistance of the strain to adverse environments. In this research, we found that adding 0.05 g/L L-cysteine to culture medium improved the freeze-drying survival rate of the strain. We investigated the internal mechanism behind this phenomenon and found that the addition of L-cysteine can reduce DNA damage to bacterial cells during the freeze-drying process. In comparison to the control group without L-cysteine, the treatment group with the addition of 0.05 g/L of L-cysteine exhibited an up-regulation of the metC gene, leading to the metabolism of L-cysteine into pyruvate and NH₃, which raised the intracellular pH, reduced DNA damage, and consequently enhanced the resistance of Lactiplantibacillus plantarum LIP-1 to freeze-drying.