Department of Life Sciences and Systems Biology, University of Torino, Torino, Italy.
Department of Life Sciences and Systems Biology, University of Torino, Torino, Italy.
J Biotechnol. 2014 Mar 10;173:31-40. doi: 10.1016/j.jbiotec.2014.01.014. Epub 2014 Jan 19.
The growing demand of biodegradable plastic polymers is increasing the industrial need of enantiospecific l-lactic acid (l-LA), the building block to produce polylactides. The most suitable industrial strategy to obtain high amounts of LA is the microbial fermentation of fruit and vegetable wastes by lactic acid bacteria (LAB). In this paper seven LAB strains from our laboratory collection, were screened for their ability to produce the highest amount of pure l-LA. A strain of Enterococcus faecium (LLAA-1) was selected and retained for further investigations. E. faecium LLAA-1 was grown in different culture media supplemented with the most abundant sugars present in agricultural wastes (i.e., glucose, fructose, cellobiose and xylose) and its ability to metabolize them to l-LA was evaluated. All tested sugars proved to be good carbon sources for the selected strain, except for xylose, which resulted in unsatisfactory biomass and LA production. Growth under aerobic conditions further stimulated l-LA production in fructose supplemented cultures with respect to anoxic-grown cultures. Proteomic profiles of E. faecium LLAA-1 grown in aerobiosis and anoxia were compared by means of two-dimensional electrophoresis followed by MALDI-TOF mass spectrometry. Seventeen proteins belonging to three main functional groups were differentially expressed: the biosynthesis of 6 proteins was up-regulated in aerobic-grown cultures while 11 proteins were biosynthesized in higher amounts in anoxia. The de novo biosynthesis of the f-subunit of alkyl hydroperoxide reductase involved in the re-oxidation of NADH seems the key element of the global re-arrangement of E. faecium LLAA-1 metabolism under aerobic conditions. An improved oxidative catabolism of proteinaceous substrates (i.e., protein hydrolisates) seems the main phenomenon allowing both higher biomass growth and improved LA production under these conditions.
可生物降解塑料聚合物的需求不断增长，这增加了对作为生产聚乳酸的单体的手性 l-乳酸（l-LA）的工业需求。获得大量 LA 的最适合工业策略是通过乳酸菌（LAB）发酵水果和蔬菜废物。在本文中，我们从实验室收集的七种 LAB 菌株进行了筛选，以确定它们生产最高量纯 l-LA 的能力。选择并保留了一株肠球菌（LLAA-1）进行进一步研究。在不同的培养基中培养肠球菌 LLAA-1，这些培养基中添加了农业废物中最丰富的糖（即葡萄糖、果糖、纤维二糖和木糖），并评估了它们将这些糖代谢为 l-LA 的能力。所有测试的糖都被证明是该选定菌株的良好碳源，除了木糖，它导致生物量和 LA 产量不理想。与缺氧生长的培养物相比，有氧条件下的生长进一步刺激了添加果糖的培养物中 l-LA 的产生。通过二维电泳和 MALDI-TOF 质谱法比较了肠球菌 LLAA-1 在需氧和缺氧条件下生长的蛋白质组图谱。属于三个主要功能组的 17 种蛋白质表现出差异表达：在有氧生长的培养物中，有 6 种蛋白质的生物合成上调，而有 11 种蛋白质在缺氧条件下生物合成更多。烷基氢过氧化物还原酶 f 亚基的从头生物合成参与 NADH 的再氧化，似乎是肠球菌 LLAA-1 在需氧条件下代谢全局重新排列的关键因素。蛋白质底物（即蛋白质水解物）的氧化分解代谢的改善似乎是在这些条件下实现更高生物量生长和提高 LA 产量的主要现象。
