A hydrogen chloride pump in extremophilic eubacteria

Acidophilic chemolithoautotrophs drive the bioleaching processes used to extract valuable metals from ores. These microorganisms thrive at extremely low pH through poorly understood mechanisms, yet remain sensitive to permeable anions such as chloride. Here, we identify and characterize P-type plasma membrane H⁺-ATPases (P3A ATPases) from Acidithiobacillus ferridurans and Geobacter metallireducens as H+/Cl− symporters − the first known primary active biological systems to export anions. This previously unrecognized ion-pumping mechanism, found to be widespread among extremophilic prokaryotes, reveals a fundamental strategy by which extremophiles achieve acid and anion tolerance. Harnessing these hydrogen chloride pumps could improve bioleaching efficiency and enable more sustainable metal recovery technologies.