Acidophiles: Diversity and mechanisms of adaptation to acidic environments

Abstract

Acidophiles are microorganisms that thrive under highly acidic conditions (pH 3 or below) and are distributed in the three domains of life: Archaea, Bacteria, and Eukarya. Among the most acidic environments on Earth are the acid mine drainage (AMD) and acid rock drainage (ARD), which are generated as a result of mining or natural weathering of sulfide minerals, respectively. Metal sulfides exposed to oxygen, water, and chemolithoautotrophic bacteria and archaea are oxidized, and highly acidic effluents enriched in toxic metals and metalloids are released from the minerals. Thus, acidophiles in these environments not only have adapted to survive at extremely low pH but also in high concentrations of metals. Thus, these microorganisms have developed networked cellular adaptations to maintain a circumneutral intracellular pH and multiple and efficient metal and metalloid resistance systems. This chapter summarizes the research on acidophiles in AMD and ARD environments: (i) their diversity and distribution in different geographical locations, (ii) mechanisms to maintain the intracellular pH homeostasis and resistance to heavy metals and metalloids, and (iii) biotechnological applications and their relevance to astrobiology.