Laboratory of Microbial Technology, Division of Systems Bioengineering, Department of Bioscience and Biotechnology, Faculty of Agriculture, Graduate School, Kyushu University, 6-10-1 Hakozaki, Higashi-Ku, Fukuoka, 812-8581, Japan.
Appl Microbiol Biotechnol. 2018 Jul;102(14):5911-5924. doi: 10.1007/s00253-018-9092-4. Epub 2018 May 26.
Lactic acid (LA) is an important platform chemical due to its significant applications in various fields and its use as a monomer for the production of biodegradable poly(lactic acid) (PLA). Free LA production is required to get rid of CaSO, a waste material produced during fermentation at neutral pH which will lead to easy purification of LA required for the production of biodegradable PLA. Additionally, there is no need to use corrosive acids to release free LA from the calcium lactate produced during neutral fermentation. To date, several attempts have been made to improve the acid tolerance of lactic acid bacteria (LAB) by using both genome-shuffling approaches and rational design based on known mechanisms of LA tolerance and gene deletion in yeast strains. However, the lack of knowledge and the complexity of acid-tolerance mechanisms have made it challenging to generate LA-tolerant strains by simply modifying few target genes. Currently, adaptive evolution has proven an efficient strategy to improve the LA tolerance of individual/engineered strains. The main objectives of this article are to summarize the conventional biotechnological LA fermentation processes to date, assess their overall economic and environmental cost, and to introduce modern LA fermentation strategies for free LA production. In this review, we provide a broad overview of free LA fermentation processes using robust LAB that can ferment in acidic environments, the obstacles to these processes and their possible solutions, and the impact on future development of free LA fermentation processes commercially.
乳酸（LA）是一种重要的平台化学品，由于其在各个领域的广泛应用以及作为生产可生物降解聚乳酸（PLA）的单体的用途。需要生产游离的 LA 以去除 CaSO，这是在中性 pH 值发酵过程中产生的废物，这将导致易于纯化生产可生物降解 PLA 所需的 LA。此外，无需使用腐蚀性酸从中性发酵过程中产生的乳酸钙中释放游离的 LA。迄今为止，已经通过使用基因组改组方法和基于已知 LA 耐受机制和酵母菌株中基因缺失的合理设计，尝试了几种提高乳酸菌（LAB）耐酸性的方法。然而，由于对酸耐受机制的了解不足和复杂性，通过简单地修饰少数目标基因来产生耐 LA 的菌株具有挑战性。目前，适应性进化已被证明是提高单个/工程菌株 LA 耐受性的有效策略。本文的主要目的是总结迄今为止传统的生物技术 LA 发酵工艺，评估其整体经济和环境成本，并介绍用于游离 LA 生产的现代 LA 发酵策略。在这篇综述中，我们广泛概述了使用能够在酸性环境中发酵的稳健 LAB 进行游离 LA 发酵的过程，讨论了这些过程的障碍及其可能的解决方案，以及对游离 LA 发酵过程未来商业发展的影响。
