Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, 78350 Jouy-en-Josas, France.
Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, 78350 Jouy-en-Josas, France.
Int J Food Microbiol. 2020 Dec 16;335:108903. doi: 10.1016/j.ijfoodmicro.2020.108903. Epub 2020 Oct 8.
Societal demand for plant-based foods is increasing. In this context, soya products fermented using lactic acid bacteria (LAB) are appealing because of their potential health and nutritional benefits. The thermophilic LAB Streptococcus thermophilus is an essential starter species in the dairy industry. However, while its physiology is well characterized, little is known about its general metabolic activity or its techno-functional properties when it is grown in soya milk. In this study, S. thermophilus LMD-9 growth, sugar production, and lactic acid production in soya milk versus cow's milk were measured. Additionally, the main metabolic pathways used by the bacterium when growing in soya milk were characterized using a proteomic approach. Streptococcus thermophilus LMD-9 growth decreased soya milk pH, from 7.5 to 4.9, in 5 h. During fermentation, acidification thus occurred in tandem with lactate production and increasing population size (final population: 1.0 × 10 CFU/ml). As growth proceeded, sucrose was consumed, and fructose was produced. The proteomic analysis (LC-MS/MS) of the strain's cytosolic and cell envelope-associated proteins revealed that proteins related to amino acid transport and nitrogen metabolism were the most common among the 328 proteins identified (63/328 = 19.2% of total proteins). The cell-wall protease PrtS was present, and an LMD-9 deletion mutant was constructed by interrupting the prtS gene (STER_RS04165 locus). Acidification levels, growth levels, and final population size were lower in the soya milk cultures when the ΔprtS strain versus the wild-type (wt) strain was used. The SDS-PAGE profile of the soluble proteins in the supernatant indicated that soya milk proteins were less hydrolyzed by the ΔprtS strain than by the wt strain. It was discovered that S. thermophilus can grow in soya milk by consuming sucrose, can hydrolyze soya proteins, and can produce acidification levels comparable to those in cow's milk. This study comprehensively examined the proteomics of S. thermophilus grown in soya milk and demonstrated that the cell-wall protease PrtS is involved in the LAB's growth in soya milk and in the proteolysis of soya proteins, which are two novel findings. These results clarify how S. thermophilus adapts to soya milk and can help inform efforts to develop new fermented plant-based foods with better-characterized biochemical and microbiological traits.
社会对植物性食品的需求正在增加。在这种情况下，由于潜在的健康和营养益处，使用乳酸菌（LAB）发酵的大豆产品很有吸引力。嗜热乳酸菌嗜热链球菌是乳制品行业中必不可少的起始物种。然而，尽管其生理学特征已经得到很好的描述，但对于其在大豆奶中的生长时的一般代谢活性或技术功能特性却知之甚少。在这项研究中，测量了嗜热链球菌 LMD-9 在大豆奶与牛奶中的生长、糖的产生和乳酸的产生。此外，还使用蛋白质组学方法来表征细菌在大豆奶中生长时使用的主要代谢途径。嗜热链球菌 LMD-9 的生长使大豆奶的 pH 值从 7.5 下降到 4.9，在 5 小时内。在发酵过程中，酸化与乳酸的产生和种群数量的增加同时发生（最终种群：1.0×10 CFU/ml）。随着生长的进行，蔗糖被消耗，果糖被产生。对菌株胞质和细胞包膜相关蛋白的蛋白质组学分析（LC-MS/MS）表明，在鉴定的 328 种蛋白中，与氨基酸转运和氮代谢相关的蛋白最为常见（328 种蛋白中的 63/328=19.2%）。存在细胞壁蛋白酶 PrtS，并通过中断 prtS 基因（STER_RS04165 基因座）构建了 LMD-9 缺失突变体。与野生型（wt）菌株相比，在大豆奶培养物中使用ΔprtS 菌株时，酸化水平、生长水平和最终种群大小均较低。上清液中可溶性蛋白的 SDS-PAGE 图谱表明，与 wt 菌株相比，大豆奶蛋白被ΔprtS 菌株水解的程度较低。研究发现，嗜热链球菌可以通过消耗蔗糖在大豆奶中生长，可以水解大豆蛋白，并产生与牛奶相当的酸化水平。这项研究全面研究了嗜热链球菌在大豆奶中的蛋白质组学，并证明细胞壁蛋白酶 PrtS 参与了 LAB 在大豆奶中的生长和大豆蛋白的水解，这是两个新发现。这些结果阐明了嗜热链球菌如何适应大豆奶，并有助于为开发具有更好生化和微生物特性的新型发酵植物性食品提供信息。
