The non-conventional yeast Pichia kudriavzevii is considered to be a promising biotechnological host for the production of organic acids under low-pH conditions. However, little is known about the low-pH stress response in P. kudriavzevii, which significantly restricts its future development. In this study, P. kudriavzevii N-X showed great tolerance to low-pH stress, but the cell aggregation upon extremely acidic conditions might be unfavorable for low-pH fermentation. We therefore conducted RNA-Seq to compare global gene expression of P. kudriavzevii N-X in response to different pH stresses. Totally 434 genes were identified to be differentially expressed genes (DEGs), and annotation and enrichment analysis suggested that multiple genes associated with regulation of membrane lipid composition, filamentous growth and arginine metabolism were differentially expressed. The increased specific activity of arginase and intracellular ammonia concentration of P. kudriavzevii cultured at pH 2.0 further implied potential roles of arginine in response to extreme low-pH conditions. Extracellular supplementation of 5 mM arginine resulted in increased pHi and cell growth at pH 2.0, meanwhile the cell aggregation was partially suppressed. Additionally, overexpression of ARG J involving in arginine synthesis can also enhance the cell growth and reduce the aggregation effect. These results suggested that increasing arginine flux might be an alternative approach in the developing of P. kudriavzevii as a platform host for production of organic acids under low-pH conditions.

非常规酵母库氏酵母被认为是在低pH条件下生产有机酸的有前途的生物技术宿主。然而，关于库氏疟原虫的低pH应激反应知之甚少，这严重限制了其未来的发展。在这项研究中，库氏假单胞菌NX对低pH胁迫表现出很大的耐受性，但在极端酸性条件下的细胞聚集可能不利于低pH发酵。因此，我们进行了RNA-Seq来比较库氏假单胞菌的整体基因表达NX响应不同的pH应力。总共鉴定出434个基因为差异表达基因（DEG），注释和富集分析表明，与膜脂成分调节，丝状生长和精氨酸代谢相关的多个基因均差异表达。在pH 2.0下培养的库氏疟原虫精氨酸酶的比活和胞内氨浓度的增加进一步暗示了精氨酸在极端低pH条件下的潜在作用。细胞外补充5 mM的精氨酸导致pHi增加，pH 2.0时细胞生长，同时部分抑制了细胞聚集。此外，ARG J的过表达参与精氨酸合成还可以增强细胞生长并降低聚集作用。这些结果表明，增加精氨酸通量可能是库氏假单胞菌作为低pH条件下生产有机酸的平台宿主的开发中的另一种方法。