Department of Bioprocess Technology, Faculty of Biotechnology and Biomolecular Sciences, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia.
Institute of Bioscience, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia.
Int J Mol Sci. 2019 Apr 10;20(7):1777. doi: 10.3390/ijms20071777.
Amino acids (AAs) are vital elements for growth, reproduction, and maintenance of organisms. Current technology uses genetically engineered microorganisms for AAs production, which has urged the search for a safer food-grade AA producer strain. The extracellular proteolytic activities of lactic acid bacteria (LAB) can be a vital tool to hydrolyze extracellular protein molecules into free AAs, thereby exhibiting great potential for functional AA production. In this study, eight LAB isolated from Malaysian foods were determined for their extracellular proteolytic activities and their capability of producing AAs. All studied LAB exhibited versatile extracellular proteolytic activities from acidic to alkaline pH conditions. In comparison, UP-2 exhibited the highest ability to produce 15 AAs extracellularly, including aspartate, lysine, methionine, threonine, isoleucine, glutamate, proline, alanine, valine, leucine, tryptophan, tyrosine, serine, glycine, and cystine, followed by UL-2, UB-6, and UP-1 with 11 to 12 different AAs production detected extracellularly. UL-6 demonstrated the highest increment of proline production at 24 h of incubation. However, UL-3 and I-UL4 exhibited the greatest requirement for AA. The results of this study showed that different LAB possess different extracellular proteolytic activities and potentials as extracellular AA producers.
氨基酸（AAs）是生物体生长、繁殖和维持所必需的要素。目前的技术使用基因工程微生物来生产 AAs，这促使人们寻找更安全的食品级 AA 生产菌株。乳酸菌（LAB）的细胞外蛋白水解活性可以成为水解细胞外蛋白质分子成游离 AAs 的重要工具，因此在功能性 AA 生产方面具有很大的潜力。在本研究中，从马来西亚食品中分离出的 8 株 LAB 被确定其细胞外蛋白水解活性及其生产 AAs 的能力。所有研究的 LAB 在从酸性到碱性 pH 值条件下均表现出多样的细胞外蛋白水解活性。相比之下，UP-2 表现出最高的能力，能够在细胞外产生 15 种 AAs，包括天冬氨酸、赖氨酸、蛋氨酸、苏氨酸、异亮氨酸、谷氨酸、脯氨酸、丙氨酸、缬氨酸、亮氨酸、色氨酸、酪氨酸、丝氨酸、甘氨酸和半胱氨酸，其次是 UL-2、UB-6 和 UP-1，分别检测到 11 到 12 种不同的 AAs 在细胞外产生。UL-6 在孵育 24 小时时表现出脯氨酸产量最高的增长。然而，UL-3 和 I-UL4 对 AA 的需求最大。本研究结果表明，不同的 LAB 具有不同的细胞外蛋白水解活性和作为细胞外 AA 生产菌的潜力。
