High values of agitation and temperature lead to stressful conditions in the fermentations of Lactococcus lactis due to its aero-tolerant and mesophilic nature. Here, the adaptive laboratory evolution (ALE) technique was applied to increase biomass and nisin production yields by enhancing L. lactis subsp. lactis robustness at higher growth temperature and aeration rates. In two separate ALE experiments, after 162 serial transfers, optimum agitation and growth temperature of L. lactis were shifted from 40 rpm and 30 °C to 200 rpm and 37 °C, respectively. Oxidative and acid resistance were enhanced in the evolved strain. Whole-genome sequencing revealed the emergence of five single-nucleotide polymorphisms in the genome of the evolved strain in jag, DnaB, ArgR, cation transporter genes, and one putative protein. The evolved strain of L. lactis in this study has more industrial desirable features and improved nisin production capability and can act more efficiently in nisin production in stressful conditions.

Graphical abstract

中文翻译：

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乳酸乳球菌对热和氧化应激的适应性进化增加了生物量和乳链菌肽的产生

由于乳酸乳球菌的耐气性和嗜温性，高搅拌和温度值会导致发酵过程中的压力条件。在这里，适应性实验室进化 (ALE) 技术被应用于通过增强乳酸乳球菌亚种来增加生物量和乳链菌肽的产量。乳酸菌在较高生长温度和通气率下的稳健性。在两个单独的 ALE 实验中，经过 162 次连续转移后，乳酸乳球菌的最佳搅拌和生长温度分别从 40 rpm 和 30 °C 转变为 200 rpm 和 37 °C。进化菌株的抗氧化性和抗酸性增强。全基因组测序揭示了进化菌株基因组中jag、DnaB、ArgR、阳离子转运蛋白基因和一种推定蛋白质的基因组中出现了五种单核苷酸多态性。本研究中进化出的乳酸乳球菌菌株具有更多的工业理想特征和提高的乳酸链球菌素生产能力，并且可以在压力条件下更有效地生产乳酸链球菌素。

图形概要