Wu Pengyu, Zhu Qiuyan, Yang Rui, Mei Yuxia, Chen Zhenmin, Liang Yunxiang
State Key Laboratory of Agricultural Microbiology, College of Life Science and Technology, Huazhong Agricultural University, Wuhan 430070, China.
Microorganisms. 2021 Sep 14;9(9):1951. doi: 10.3390/microorganisms9091951.
Liquid-state fermentation (LSF) and solid-state fermentation (SSF) are two forms of industrial production of lactic acid bacteria (LAB). The choice of two fermentations for LAB production has drawn wide concern. In this study, the tolerance of bacteria produced by the two fermentation methods to acid stress was compared, and the reasons for the tolerance differences were analyzed at the physiological and transcriptional levels. The survival rate of the bacterial agent obtained from solid-state fermentation was significantly higher than that of bacteria obtained from liquid-state fermentation after spray drying and cold air drying. However, the tolerance of bacterial cells obtained from liquid-state fermentation to acid stress was significantly higher than that from solid-state fermentation. The analysis at physiological level indicated that under acid stress, cells from liquid-state fermentation displayed a more solid and complete membrane structure, higher cell membrane saturated fatty acid, more stable intracellular pH, and more stable activity of ATPase and glutathione reductase, compared with cells from solid-state fermentation, and these physiological differences led to better tolerance to acid stress. In addition, transcriptomic analysis showed that in the cells cultured from liquid-state fermentation, the genes related to glycolysis, inositol phosphate metabolism, and carbohydrate transport were down-regulated, whereas the genes related to fatty acid synthesis and glutamate metabolism were upregulated, compared with those in cells from solid-state fermentation. In addition, some genes related to acid stress response such as , , , , and were up-regulated. These findings provide a new perspective for the study of acid stress tolerance of Zhang and offer a reference for the selection of fermentation methods of LAB production.
液态发酵（LSF）和固态发酵（SSF）是乳酸菌（LAB）工业生产的两种形式。选择这两种发酵方式来生产乳酸菌已引起广泛关注。在本研究中，比较了两种发酵方法所产细菌对酸胁迫的耐受性，并在生理和转录水平分析了耐受性差异的原因。经过喷雾干燥和冷风干燥后，固态发酵获得的菌剂存活率显著高于液态发酵获得的细菌。然而，液态发酵获得的细菌细胞对酸胁迫的耐受性显著高于固态发酵获得的细菌。生理水平分析表明，在酸胁迫下，与固态发酵获得的细胞相比，液态发酵获得的细胞呈现出更坚实和完整的膜结构、更高的细胞膜饱和脂肪酸含量、更稳定的细胞内pH值以及更稳定的ATP酶和谷胱甘肽还原酶活性，这些生理差异导致对酸胁迫具有更好的耐受性。此外，转录组分析表明，与固态发酵获得的细胞相比，液态发酵培养的细胞中，与糖酵解、肌醇磷酸代谢和碳水化合物转运相关的基因下调，而与脂肪酸合成和谷氨酸代谢相关的基因上调。此外，一些与酸胁迫应答相关的基因如 、 、 、 和 上调。这些发现为研究张的酸胁迫耐受性提供了新的视角，并为乳酸菌生产发酵方法的选择提供了参考。
