College of Chemical Engineering, Huaqiao University, 668 Jimei Boulevard, Xiamen, Fujian 361021, P. R. China.
J Agric Food Chem. 2020 Jul 22;68(29):7660-7669. doi: 10.1021/acs.jafc.0c00259. Epub 2020 Jul 13.
To decrease d-lactic acid production cost, sugarcane molasses and soybean meal, low-cost agro-industrial wastes, were selected as feedstock. First, sugarcane molasses was used directly by S-NL31, and the nutrients were released from soybean meal by protease hydrolysis. Subsequently, to ensure intensive substrate utilization and enhanced d-lactic acid production from sugarcane molasses and soybean meal, adaptation of S-NL31 to substrates was performed through adaptive laboratory evolution. After two-phase adaptive laboratory evolution, the evolved strain S-NL31-CM3-SBM with improved cell growth and d-lactic acid production on sugarcane molasses and soybean meal was obtained. To decipher the potential reasons for improved fermentation performance, a metabolomics-based approach was developed to profile the differences of intracellular metabolism between initial and evolved strain. The in-depth analysis elucidated how the key factors exerted influence on d-lactic acid biosynthesis. The results revealed that the enhancement of glycolysis pathway and cofactor supply was directly associated with increased lactic acid production, and the reinforcement of pentose phosphate pathway, amino acid metabolism, and oleic acid uptake improved cell survival and growth. These might be the main reasons for significantly improved d-lactic acid production by adaptive laboratory evolution. Finally, fed-batch simultaneous enzymatic hydrolysis of soybean meal and fermentation process by evolved strain resulted in d-lactic acid levels of 112.3 g/L, with an average production efficiency of 2.4 g/(L × h), a yield of 0.98 g/g sugar, and optical purity of 99.6%. The results show the applicability of d-lactic acid production in fed on agro-industrial wastes through adaptive laboratory evolution.
为了降低 D-乳酸的生产成本，选择了甘蔗蜜和豆粕这两种低成本的农业工业废物作为原料。首先，S-NL31 直接利用甘蔗蜜，蛋白酶水解释放豆粕中的营养物质。随后，为了确保从甘蔗蜜和豆粕中强化基质利用和增强 D-乳酸的生产，通过适应性实验室进化来适应 S-NL31 对基质的利用。经过两相适应性实验室进化，获得了具有改良的细胞生长和在甘蔗蜜和豆粕上生产 D-乳酸能力的进化菌株 S-NL31-CM3-SBM。为了解释发酵性能提高的潜在原因，开发了一种基于代谢组学的方法来分析初始菌株和进化菌株之间的细胞内代谢差异。深入分析阐明了关键因素如何对 D-乳酸生物合成产生影响。结果表明，糖酵解途径和辅酶供应的增强与乳酸产量的增加直接相关，而戊糖磷酸途径、氨基酸代谢和油酸摄取的增强改善了细胞的生存和生长。这些可能是适应性实验室进化显著提高 D-乳酸生产的主要原因。最后，通过进化菌株同时进行酶解豆粕和发酵的补料分批发酵工艺，得到了 112.3 g/L 的 D-乳酸水平，平均生产效率为 2.4 g/（L×h），糖得率为 0.98 g/g，光学纯度为 99.6%。结果表明，通过适应性实验室进化，从农业工业废物中进行 D-乳酸生产是可行的。
