Biodiversity and ecology of acidophilic microorganisms

Abstract

Microbial life in extremely low pH (<3) natural and man‐made environments may be considerably diverse. Prokaryotic acidophiles (eubacteria and archaea) have been the focus of much of the research activity in this area, primarily because of the importance of these microorganisms in biotechnology (predominantly the commercial biological processing of metal ores) and in environmental pollution (genesis of ‘acid mine drainage’); however, obligately acidophilic eukaryotes (fungi, yeasts, algae and protozoa) are also known, and may form stable microbial communities with prokaryotes, particularly in lower temperature (<35°C) environments. Primary production in acidophilic environments is mediated by chemolitho‐autotrophic prokaryotes (iron and sulfur oxidisers), and may be supplemented by phototrophic acidophiles (predominantly eukaryotic microalgae) in illuminated sites. The most thermophilic acidophiles are archaea (Crenarchaeota) whilst in moderately thermal (40–60°C) acidic environments archaea (Euryarchaeota) and bacteria (mostly Gram‐positives) may co‐exist. Lower temperature (mesophilic) extremely acidic environments tend to be dominated by Gram‐negative bacteria, and there is recent evidence that mineral oxidation may be accelerated by acidophilic bacteria at very low (ca. 0°C) environments. Whilst most acidophiles have conventionally been considered to be obligately aerobic, there is increasing evidence that many isolates are facultative anaerobes, and are able to couple the oxidation of organic or inorganic electron donors to the reduction of ferric iron. A variety of interactions have been demonstrated to occur between acidophilic microorganisms, as in other environments; these include competition, predation, mutualism and synergy. Mixed cultures of acidophiles are frequently more robust and efficient (e.g. in oxidising sulfide minerals) than corresponding pure cultures. In view of the continuing expansion of microbial mineral processing (‘biomining’) as a cost‐effective and environmentally sensitive method of metal extraction, and the ongoing concern of pollution from abandoned mine sites, acidophilic microbiology will continue to be of considerable research interest well into the new millennium.

Cultivation and quantitative proteomic analyses of acidophilic microbial communities

“…In the laboratory community, increased archaeal stress response proteins correlated with the stress response of Leptospirillum group II. As community production is likely dependent on all microbial species because of mutualistic and synergistic interactions (Hallmann et al, 1992;Johnson, 1998), stress to the archaea may have further decreased net production and growth rates in laboratory reactors.…”

Potential for Microscale Bacterial Fe Redox Cycling at the Aerobic-Anaerobic Interface

“…Bacterial catalysis is also likely to play an Tebo and He (1999), copyright 2000 American Chemical Society. Recent reviews of the role of microbial activity in the various processes are indicated by the superscripted letters: (a) circumneutral pH: Lovley (2000), Thamdrup (2000); acidic pH: Johnson (1998), Blake and Johnson (2000), see also Küsel et al (1999) and Peine et al (2000) (b) circumneutral pH: direct enzymatic catalysis doubtful; see Thamdrup et al (1993), Lovley (1994), and Schippers and Jørgensen (2001); acidic pH: Blake and Johnson (2000), Pronk and Johnson (1992). (2000); acidic pH: Johnson (1998), Blake and Johnson (2000); see also Edwards et al (2000).…”

Quantitative proteomic analyses of the response of acidophilic microbial communities to different pH conditions

“…Low complexity, extremophilic consortia that thrive in acid mine drainage (AMD) environments have been proposed as a model system for the study of natural microbial communities (Denef et al, 2010b). Ecological interactions such as competition, mutualism, predation and synergism have been described in such environments (Johnson, 1998). AMD biofilm communities from the Richmond Mine at Iron Mountain, CA, USA have been well characterized using culture independent techniques (Edwards et al, 1999;Bond et al, 2000a, b;Druschel et al, 2004;Wilmes et al, 2008b), and have also been the subject of intensive genomic and proteomic studies (Tyson et al, 2004;Ram et al, 2005;Lo et al, 2007;Simmons et al, 2008;Denef et al, 2009), making them ideal for in-depth ecological analyses.…”