Molecular insights into the response of Acidithiobacillus caldus to leached metal toxicity during bioleaching of spent FCC catalyst

Acidithiobacillus caldus , a thermoacidophilic sulfur-oxidizing bacterium, is utilized in bioleaching owing to its robust metabolic capabilities.To elucidate the adaptive mechanisms of A. caldus to metal toxicity during bioleaching of spent fluid catalytic cracking catalyst (SFCCC), an integrated approach was employed, encompassing dynamic monitoring of metal release, enzymatic activity assays, and de novo transcriptome sequencing. This study systematically deciphered the synergistic mechanism of “leaching promotion–toxicity response–resistance regulation” in A. caldus under SFCCC-induced stress. The bacterium demonstrated high leaching efficiency of heavy metals from SFCCC. Under metal-induced stress, it employed defense mechanisms primarily through a glutathione peroxidase (GSH-Px)-mediated antioxidant system. This response was sustained by the continuous activation of H⁺-ATPase and NADPH-generating metabolic pathways to maintain energy and reduce supply. The bacterial response exhibited concentration dependence: under low-concentration stress, it prioritized basal metabolic maintenance alongside initiation of defensive measures; under high-concentration stress, it employed a comprehensive survival strategy involving metabolic reprogramming to sacrifice non-essential functions in favor of critical survival processes. This transition reflects a strategic shift from a “growth-oriented” to a “survival-oriented” mode. These findings enhance the theoretical framework for understanding concentration-dependent strategic transitions in microbe-metal interactions and offer a molecular biology basis for improving the practical application of bioleaching technologies.