Metabolic engineering is a substantial approach for escalating the production of biochemical products. Cell biomass is lowered by system constraints and toxication carried on by the aggregation of metabolites that serve as inhibitors of product synthesis. In order to increase the production of biochemical products, it is important to trace the relationship between alanine metabolism and biomass. According to our investigation, the appropriate concentration of additional L/D-alanine (0.1 g/L) raised the cell biomass (OD₆₀₀) in Bacillus licheniformis in contrast to the control strain. Remarkably, it was also determined that high levels of intracellular L/D-alanine and D-alanyl-D-alanine were induced by the overexpression of the ald, dal, and ddl genes to accelerate cell proliferation. Our findings clearly revealed that 0.2 g/L of L-alanine and D-alanine substantially elevated the titer of poly-γ-glutamic acid (γ-PGA) by 14.89% and 6.19%, correspondingly. And the levels of γ-PGA titer were hastened by the overexpression of the ald, dal, and ddl genes by 19.72%, 15.91%, and 16.64%, respectively. Furthermore, overexpression of ald, dal, and ddl genes decreased the by-products (acetoin, 2,3-butanediol, acetic acid and lactic acid) formation by about 14.10%, 8.77%, and 8.84% for augmenting the γ-PGA production. Our results also demonstrated that overexpression of ald gene amplified the production of lichenysin, pulcherrimin and nattokinase by about 18.71%, 19.82% and 21.49%, respectively. This work delineated the importance of the L/D-alanine and D-alanyl-D-alanine synthesis to the cell growth and the high production of bio-products, and provided an effective strategy for producing bio-products.

代谢工程是提高生化产品产量的重要方法。细胞生物量因系统限制和由作为产物合成抑制剂的代谢物聚集而产生的毒性而降低。为了增加生化产品的产量，重要的是追踪丙氨酸代谢和生物量之间的关系。根据我们的调查，与对照菌株相比，适当浓度的额外 L/D-丙氨酸 (0.1 g/L) 提高了地衣芽孢杆菌中的细胞生物量 (OD ₆₀₀ ) 。值得注意的是，还确定了高水平的细胞内 L/D-丙氨酸和 D-丙氨酰-D-丙氨酸是由 ald 、 dal的过表达诱导的和ddl基因加速细胞增殖。我们的研究结果清楚地表明，0.2 g/L 的 L-丙氨酸和 D-丙氨酸显着提高了聚-γ-谷氨酸 (γ-PGA) 的滴度，相应地提高了 14.89% 和 6.19%。γ-PGA 效价水平因ald、dal和ddl基因的过表达而分别加快了 19.72%、15.91% 和 16.64%。此外，ald、dal和ddl基因的过表达使副产物（乙偶姻、2,3-丁二醇、乙酸和乳酸）的形成减少了约 14.10%、8.77% 和 8.84%，从而增加了 γ-PGA 的产量. 我们的结果还表明ald的过度表达基因将地衣素、pulcherrimin 和纳豆激酶的产量分别放大了约 18.71%、19.82% 和 21.49%。这项工作描述了 L/D-丙氨酸和 D-丙氨酰-D-丙氨酸合成对细胞生长和生物产品高产量的重要性，并为生产生物产品提供了有效的策略。