acidophiles

Acidophiles are microorganisms that prefer or require acidic conditions, typically thriving at pH values below about 3. Some tolerate values up to around pH 5. They include bacteria, archaea, and, to a lesser extent, some fungi and algae, with bacteria and archaea providing the best-studied representatives. Common acidophilic bacteria include Acidithiobacillus ferrooxidans, Acidithiobacillus thiooxidans, Leptospirillum ferrooxidans, and Ferroplasma species, while notable archaea include Picrophilus torridus and members of the Thermoplasmatales.

Physiologically, acidophiles maintain a near-neutral cytoplasmic pH despite an acidic exterior. They achieve this with robust proton extrusion systems, selective membrane lipids that limit proton permeability, and adaptive stress responses. Their enzymes and proteins are adapted to function under acidic conditions, and they often employ efficient DNA repair and chaperone networks to cope with acid-induced damage.

Ecologically, acidophiles inhabit acidic environments such as acid mine drainage, acidic hot springs, acidic soils, and industrial residues. They play key roles in biogeochemical cycles, especially iron and sulfur oxidation, which can drive acidification and metal solubilization. In applied settings, acidophiles are exploited for bioleaching and biomining of sulfide ores, and for treatment of acidic effluents and contaminated metals, though their activity can also contribute to environmental pollution if uncontrolled.

Diversity and extremophily vary; extremely acidophilic archaea such as Picrophilus torridus grow at near-zero pH, while many acidophilic bacteria operate best around pH 2–3. Understanding their physiology informs both ecology and industrial biotechnology.