High-quality environmentally-friendly bioplastics can be produced by mixing poly-L-lactate with poly-D-lactate. On an industrial scale, this process simultaneously consumes large amounts of both optically pure lactate stereoisomers. However, because optimal growth conditions of L-lactate producers often differ from those of D-lactate producers, each stereoisomer is produced in a specialised facility, which raises cost and lowers sustainability. To address this challenge, we metabolically engineered Lactobacillus gasseri JCM 1131T, a bioprocess-friendly and genetically malleable strain of homofermentative lactic acid bacterium, to efficiently produce either pure L- or pure D-lactate under the same bioprocess conditions. Transformation of L. gasseri with plasmids carrying additional genes for L- or D-lactate dehydrogenases failed to affect the ratio of produced stereoisomers, but inactivation of the endogenous genes created strains which yielded 0.96 g of either L- or D-lactate per gram of glucose. In this study, the plasmid pHBintE, routinely used for gene disruption in Bacillus megaterium, was used for the first time to inactivate genes in lactobacilli. Strains with inactivated genes for endogenous lactate dehydrogenases efficiently fermented sugars released by enzymatic hydrolysis of alkali pre-treated wheat straw, an abundant lignocellulose-containing raw material, producing 0.37-0.42 g of lactate per gram of solid part of alkali-treated wheat straw. Thus, the constructed strains are primed to serve as producers of both optically pure L-lactate and D-lactate in the next-generation biorefineries.

中文翻译：

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代谢工程加氏乳杆菌 JCM 1131 作为光学纯 L-和 D-乳酸的新型生产者

通过将聚-L-乳酸与聚-D-乳酸混合，可以生产高质量的环保生物塑料。在工业规模上，该过程同时消耗大量光学纯乳酸立体异构体。然而，由于 L-乳酸生产商的最佳生长条件通常与 D-乳酸生产商不同，每种立体异构体都是在专门的设施中生产的，这会增加成本并降低可持续性。为了应对这一挑战，我们通过代谢工程改造了加氏乳杆菌 JCM 1131T，这是一种生物工艺友好且具有遗传可塑性的同型发酵乳酸菌菌株，可在相同的生物工艺条件下有效地生产纯 L- 或纯 D-乳酸。L 的变换。带有携带 L- 或 D- 乳酸脱氢酶额外基因的质粒的 Gasseri 未能影响产生的立体异构体的比例，但内源基因的失活产生了每克葡萄糖产生 0.96 g L- 或 D-乳酸的菌株。在这项研究中，常规用于巨大芽孢杆菌基因破坏的质粒 pHBintE 首次用于灭活乳酸杆菌中的基因。内源性乳酸脱氢酶基因失活的菌株有效发酵碱预处理小麦秸秆（一种丰富的含木质纤维素原料）酶水解释放的糖，每克碱处理小麦秸秆固体部分可产生 0.37-0.42 克乳酸。因此，