Guangdong Key Laboratory of Fermentation and Enzyme Engineering, School of Bioscience and Bioengineering, South China University of Technology, Guangzhou 510006, China.
Biotechnol Biofuels. 2013 Aug 28;6(1):124. doi: 10.1186/1754-6834-6-124.
Efficient conversion of lignocellulosic biomass to optically pure lactic acid is a key challenge for the economical production of biodegradable poly-lactic acid. A recently isolated strain, Thermoanaerobacterium aotearoense SCUT27, is promising as an efficient lactic acid production bacterium from biomass due to its broad substrate specificity. Additionally, its strictly anaerobic and thermophilic characteristics suppress contamination from other microoragnisms. Herein, we report the significant improvements of concentration and yield in lactic acid production from various lignocellulosic derived sugars, achieved by the carbon flux redirection through homologous recombination in T. aotearoense SCUT27.
T. aotearoense SCUT27 was engineered to block the acetic acid formation pathway to improve the lactic acid production. The genetic manipulation resulted in 1.8 and 2.1 fold increase of the lactic acid yield using 10 g/L of glucose or 10 g/L of xylose as substrate, respectively. The maximum l-lactic acid yield of 0.93 g/g glucose with an optical purity of 99.3% was obtained by the engineered strain, designated as LA1002, from 50 g/L of substrate, which is very close to the theoretical value (1.0 g/g of glucose). In particular, LA1002 produced lactic acid at an unprecedented concentration up to 3.20 g/L using 10 g/L xylan as the single substrate without any pretreatment after 48 h fermentation. The non-sterilized fermentative production of l-lactic acid was also carried out, achieving values of 44.89 g/L and 0.89 g/g mixed sugar for lactic acid concentration and yield, respectively.
Blocking acetic acid formation pathway in T. aotearoense SCUT27 increased l-lactic acid production and yield dramatically. To our best knowledge, this is the best performance of fermentation on lactic acid production using xylan as the sole carbon source, considering the final concentration, yield and fermentation time. In addition, it should be mentioned that the performance of non-sterilized simultaneous fermentation from glucose and xylose was very close to that of normal sterilized cultivation. All these results used the mutant strain, LA1002, indicated that it is a new promising candidate for the effective production of optically pure l-lactic acid from lignocellulosic biomass.
将木质纤维素生物质高效转化为光学纯乳酸是经济生产可生物降解聚乳酸的关键挑战。最近分离的Thermoanaerobacterium aotearoense SCUT27 菌株由于其广泛的底物特异性，有望成为一种从生物质中高效生产乳酸的细菌。此外，其严格的厌氧和嗜热特性抑制了其他微生物的污染。在此，我们通过同源重组在 T. aotearoense SCUT27 中进行碳通量重定向，报告了在各种木质纤维素衍生糖中提高乳酸产量和浓度的显著改进。
为了提高乳酸产量，我们对 T. aotearoense SCUT27 进行了工程改造以阻断乙酸形成途径。遗传操作使 10 g/L 葡萄糖或 10 g/L 木糖作为底物时的乳酸产量分别提高了 1.8 倍和 2.1 倍。用工程菌株 LA1002 从 50 g/L 底物中获得了最大的 l-乳酸产量 0.93 g/g 葡萄糖，光学纯度为 99.3%，这非常接近理论值（1.0 g/g 葡萄糖）。特别是，LA1002 在未经任何预处理的情况下，以 10 g/L 木聚糖作为唯一底物，48 h 发酵后乳酸浓度达到 3.20 g/L，达到了前所未有的水平。还进行了非灭菌发酵生产 l-乳酸，乳酸浓度和产率分别达到 44.89 g/L 和 0.89 g/g 混合糖。
在 T. aotearoense SCUT27 中阻断乙酸形成途径可显著提高 l-乳酸的产量和产率。据我们所知，考虑到最终浓度、产率和发酵时间，这是使用木聚糖作为唯一碳源发酵生产乳酸的最佳性能。此外，值得一提的是，未经灭菌的葡萄糖和木糖同时发酵的性能与正常灭菌培养非常接近。所有这些结果均使用突变株 LA1002 获得，表明它是从木质纤维素生物质有效生产光学纯 l-乳酸的一种很有前途的新候选菌株。
