Carbonic Anhydrases in Mycobacteria: Linking Metabolic Adaptation to Phenotypic Drug Tolerance.

Tuberculosis (TB) treatment is increasingly challenged by both antimicrobial resistance (AMR) and phenotypic drug tolerance, the latter representing a reversible physiological state that contributes to persistence and prolonged therapy. While AMR is driven by heritable genetic mutations, drug tolerance arises from reversible physiological adaptations that enable bacterial survival during prolonged antibiotic exposure. Increasing evidence suggests that metabolic remodeling plays a central role in establishing these drug-tolerant states. Carbonic anhydrases (CAs) are zinc-containing metalloenzymes that catalyze the reversible interconversion of carbon dioxide and bicarbonate, thereby maintaining intracellular pH homeostasis and supporting bicarbonate-dependent metabolism. Beyond their established metabolic functions, indirect evidence suggests that CAs may contribute to physiological adaptations associated with bacterial persistence under host-imposed stresses, including hypoxia, nutrient limitation, and acidic environments. Although they are not classical AMR determinants, CAs may influence the metabolic landscape associated with phenotypic drug tolerance. In this review, we examine current evidence supporting the role of CAs in mycobacterial metabolism and propose a conceptual framework linking bicarbonate homeostasis, intracellular pH regulation, and metabolic adaptation to bacterial persistence and drug tolerance. We further discuss the potential of carbonic anhydrase inhibitors (CAIs) as adjunctive agents whose ability to enhance the activity of conventional antitubercular drugs requires experimental validation, together with the value of experimental models, including the Mycobacterium marinum-zebrafish system, and computational approaches for validating CA-targeted therapeutic strategies. Overall, this review highlights CAs as candidate metabolic regulators that may influence the physiological state underlying phenotypic drug tolerance. Defining their mechanistic contribution to persistence could facilitate the development of metabolism-based therapeutic strategies that complement existing TB treatment.