acidophile

An acidophile is an organism that prefers or requires acidic conditions for growth. In microbiology, acidophiles are typically defined as organisms with an optimum growth pH below 3, though some thrive at pH values as high as around 4 or 5.

Acidophiles occur in environments inhospitable to most life, including acidic hot springs, volcanic soils, acidic mine drainage, sulfate-rich sediments, and acidic waters associated with mining or volcanic activity. They play important roles in biogeochemical cycles of iron and sulfur, often as chemolithoautotrophs that oxidize reduced inorganic compounds.

Many acidophiles are prokaryotes, especially bacteria and archaea. They have evolved mechanisms to maintain a near-neutral cytoplasmic pH in the face of acidic surroundings, including efficient proton pumps and membrane adaptations that limit proton permeability. Some are thermophilic or thermoacidophilic, thriving at high temperatures in addition to low pH.

Prominent examples include chemolithoautotrophic acidophiles such as Acidithiobacillus and Leptospirillum, which oxidize ferrous iron and reduced sulfur compounds. There are also extremely acidophilic archaea such as Picrophilus and some Thermoplasmatales. These organisms often dominate microbial communities in acidic environments and influence acid formation and metal mobility.

Applications of acidophiles include bioleaching and biomining, where they mobilize metals from sulfide ores, and bioremediation of acidic industrial effluents. Research on acidophiles contributes to understanding the limits of life and offers insights into ancient biogeochemical processes.