Key Laboratory of Dairy Biotechnology and Engineering, Education Ministry of P. R. China, Department of Food Science and Engineering, Inner Mongolia Agricultural University, Hohhot, PR China; Key Laboratory of Dairy Products Processing, Ministry of Agriculture, Department of Food Science and Engineering, Inner Mongolia Agricultural University, Hohhot, PR China.
Food Res Int. 2021 Nov;149:110694. doi: 10.1016/j.foodres.2021.110694. Epub 2021 Sep 4.
The growth and the resistance to adverse environments of lactic acid bacteria would be affected by adjusting the initial pH of the medium. In order to explore the effect of changing the initial pH of culture medium on the freeze-drying survival rate of the Lactiplantibacillus plantarum LIP-1, the effect of initial pH on cell membrane fatty acid composition and key enzyme activity were mainly determined, and the internal mechanism was studied by transcriptomics and proteomics methods. We found that compared with initial pH 7.4 group, initial pH 6.8 group could improve the freeze-drying survival rate of the L. plantarum LIP-1. It was possibly due to the lactate dehydrogenase (LDH) was upregulated in the initial pH6.8 group, which led to a rapid decrease in culture pH. To reduce the inhibitory effect of long-term acid environment on growth, the strain upregulated the expression of fatty acid synthesis-related genes and proteins, promoted the relative content of cyclopropane and unsaturated fatty acids, improved integrity of the cell membranes. The adjustment of fatty acid composition maintained the integrity of the cell membrane in a freeze-drying environment to improve the freeze-drying survival rate of the initial pH6.8 group. In addition, the long-term acid environment stimulated a cross-stress tolerance mechanism that significantly upregulated the expression of a cold stress protein. The results indicated that the optimal initial pH of the medium could improve the ability of L. plantarum LIP-1 to resist freeze-drying.
初始培养基 pH 值的调整会影响乳酸菌的生长和抗逆性。为了探究改变培养基初始 pH 值对植物乳杆菌 LIP-1 冻干存活率的影响，本研究主要测定了初始 pH 值对细胞膜脂肪酸组成和关键酶活性的影响，并通过转录组学和蛋白质组学方法研究了内部机制。研究发现，与初始 pH7.4 组相比，初始 pH6.8 组可提高 L. plantarum LIP-1 的冻干存活率。这可能是因为初始 pH6.8 组中乳酸脱氢酶（LDH）上调，导致培养 pH 值迅速下降。为了降低长期酸性环境对生长的抑制作用，该菌株上调了脂肪酸合成相关基因和蛋白的表达，促进了环丙烷和不饱和脂肪酸的相对含量增加，提高了细胞膜的完整性。脂肪酸组成的调整保持了细胞膜在冻干环境中的完整性，从而提高了初始 pH6.8 组的冻干存活率。此外，长期酸性环境刺激了一种交叉胁迫耐受机制，显著上调了冷应激蛋白的表达。结果表明，优化培养基的初始 pH 值可以提高植物乳杆菌 LIP-1 抵抗冻干的能力。
