β-poly(L-malic acid) (PMLA) has attracted industrial interest for its potential applications in medicine and other industries. For a sustainable PMLA production, it requires replacing/reducing the CaCO3 usage, since the residual CaCO3 impeded the cells' utilization, and a large amount of commercially useless gypsum was accumulated. In this study, it was found that more glucose was converted into CO2 using soluble alkalis compared with CaCO3 usage. Moreover, since the high ion strength and respiration effect of soluble alkalis also inhibited PMLA production, they could not effectively replace CaCO3. Furthermore, comparing the fermentations with different neutralizers (soluble alkali vs. CaCO3), it was found that the differential genes are mainly involved in the pathway of starch and sucrose metabolism, pentose and glucuronate interconversions, histidine metabolism, ascorbate and aldarate metabolism, and phagosome. In detail, in the case with CaCO3, 562 genes were downregulated and 262 genes were upregulated, and especially, those genes involved in energy production and conversion were downregulated by 26.7%. Therefore, the irreplaceability of CaCO3 was caused by its effect on the PMLA metabolic pathway rather than its usage as neutralizer. Finally, a combined pH shift control strategy with CaCO3 addition was developed. After the fermentation, 64.8 g/L PMLA and 38.9 g/L biomass were obtained with undetectable CaCO3 and less CO2 emission. KEY POINTS: • The effect of CaCO3 on PMLA metabolic pathway resulted in its irreplaceability. • A pH shift control strategy with CaCO3 addition was developed. • Undetectable CaCO3 and less CO2 emission were detected with the new strategy. Graphical abstract.

中文翻译：

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Aureobasidium pullulans ipe-1通过添加CaCO3高效生产β-聚（L-苹果酸）的可持续pH值控制策略。

β-聚（L-苹果酸）（PMLA）因其在医学和其他行业中的潜在应用而引起了工业兴趣。对于可持续的PMLA生产，需要更换/减少CaCO3的使用，因为残留的CaCO3会阻碍细胞的利用，并且会积累大量无商业用途的石膏。在这项研究中，发现与使用CaCO3相比，使用可溶性碱将更多的葡萄糖转化为CO2。而且，由于可溶性碱的高离子强度和呼吸作用也抑制了PMLA的产生，因此它们不能有效替代CaCO3。此外，将发酵液与不同的中和剂（可溶性​​碱与CaCO3）进行比较，发现差异基因主要参与淀粉和蔗糖代谢，戊糖和葡萄糖醛酸酯相互转化的途径，组氨酸代谢，抗坏血酸盐和藻酸盐代谢以及吞噬体。详细地，在CaCO 3的情况下，下调了562个基因，上调了262个基因，特别是那些涉及能量产生和转化的基因下调了26.7％。因此，CaCO3的不可替代性是由其对PMLA代谢途径的影响而不是其用作中和剂引起的。最后，开发了一种结合添加CaCO3的pH改变控制策略。发酵后，获得了64.8 g / L的PMLA和38.9 g / L的生物质，且未检测到CaCO3，且CO2排放量较少。要点：•CaCO3对PMLA代谢途径的影响导致其不可替代性。•开发了添加CaCO3的pH改变控制策略。•使用新策略可检测到无法检测到的CaCO3和更少的CO2排放。