AspA activity orchestrates a growth-stress survival trade-off in Yersinia pestis via metabolic reprogramming

The aspA gene of Yersinia pestis exhibits a pronounced polymorphism at codon 363, with the dominant TTG allele encoding an inactive aspartate ammonia-lyase (AspA) while the GTG allele encoding an active enzyme. We previously demonstrated that this polymorphism drives an environment-dependent fitness trade-off, yet the underlying mechanism remains unclear. To address this, we first characterized the phenotypic differences between the two strains and revealed a clear growth-stress survival trade-off: the GTG (AspA-active) strain grew faster and produced more ATP, whereas the TTG (AspA-inactive) strain, despite slower growth, exhibited superior survival under nutrient limitation with oxidative, anaerobic, or hyperosmotic stress. Exogenous aspartate reversed the GTG strain's disadvantages under anaerobic or cold stress. To dissect the metabolic basis, we performed ¹³C-labeled metabolic flux analysis on these two strains. The GTG strain rapidly converted aspartate to fumarate via AspA, fueling the TCA cycle and boosting ATP production. In contrast, the TTG strain displayed stalled aspartate utilization and accumulated amino acids and lipids. Supplementation with TCA cycle intermediates (fumarate, succinate, or malate) partially rescued TTG growth, confirming that reduced TCA flux limits its proliferation. Collectively, AspA activity orchestrates a growth-stress survival trade-off through metabolic reprogramming, underlying the antagonistic pleiotropy of Y. pestis in aspartate-available or stressful environments. The "metabolic congestion" strategy of the TTG strain enhances survival under multiple stresses relevant to the flea gut, and it is plausible that this metabolic reprogramming may contribute to transmission and provide a selective advantage under flea-borne conditions.IMPORTANCEThe plague bacterium Yersinia pestis encounters oxidative, anaerobic, and hyperosmotic stresses-conditions relevant to its flea gut environment during transmission. This study reveals that a single, naturally occurring polymorphism in the aspA gene shifts the bacterium's metabolism from a growth-focused mode to a "metabolic congestion" state that enhances survival under these stresses in vitro. Our work provides a mechanistic framework for understanding how metabolic reprogramming could influence adaptation to vector-like conditions, offering a plausible basis for the environment-dependent fitness trade-offs that may shape transmission dynamics.