The influence of glutathione metabolism on alkaline adaptation of Amur ide (Leuciscus waleckii) and potential role of gut microbiota.

Amur ide (Leuciscus waleckii), which inhabits Lake Dali, a soda lake in Northeast China with extremely high alkalinity (~ 53.57 mmol/L) and pH value (~ 9.6), is considered to be an ideal model for elucidating alkaline adaption mechanisms. To uncover the molecular mechanisms underlying this adaptation, we conducted a comparative study between the alkaline water ecotype (JY) and freshwater ecotype (DY). Both groups were exposed to a gradient of NaHCO₃ stress levels (0, 10, 30, and 50 mmol/L), and their responses were systematically assessed through integrated multi-omics analyses alongside physiological assays. Our results revealed that under low and moderate alkaline stress (10 and 30 mmol/L), JY group significantly upregulated the gene anpep, facilitating the hydrolysis of cysteinyl-glycine to release L-cysteine, thereby enhancing antioxidant capacity. Under high stress conditions (50 mmol/L), JY further synergistically upregulated gpx to activated the glutathione peroxidase (GPx) pathway to eliminate excess ROS. In contrast, the DY group predominantly relied on upregulating chac1-mediated γ-glutamyltransferase activity to facilitate glutathione cycling. Notably, while cysteinyl-glycine content significantly increased in the alkaline water ecotype (JY) under moderate and high alkalinity stress (30 and 50 mmol/L), the expression of its upstream gene chac1 was significantly downregulated. This paradox suggests alternative sources or regulatory mechanisms for cysteinyl-glycine accumulation in JY. Microbial tracing analysis revealed a positive correlation between cysteinyl-glycine levels and the gut microbiota genus Stenotrophomonas in JY, whose relative abundance increased progressively with elevated alkalinity. It is speculated that Stenotrophomonas may modulate host glutathione metabolism by regulating cysteinyl-glycine levels, thereby facilitating alkaline adaptation.