Biocatalizadores

Extremophiles (2012) 16:1–19 DOI 10.1007/s00792-011-0402-3

REVIEW

Acidophilic bacteria and archaea: acid stable biocatalysts and their potential applications
Archana Sharma • Yutaka Kawarabayasi T. Satyanarayana
•

Received: 10 August 2010 / Accepted: 5 October 2011 / Published online: 13 November 2011 Ó Springer 2011

Abstract Acidophiles are ecologically and economically importantgroup of microorganisms, which thrive in acidic natural (solfataric fields, sulfuric pools) as well as artificial man-made (areas associated with human activities such as mining of coal and metal ores) environments. They possess networked cellular adaptations to regulate pH inside the cell. Several extracellular enzymes from acidophiles are known to be functional at much lower pH than the cytoplasmicpH. Enzymes like amylases, proteases, ligases, cellulases, xylanases, a-glucosidases, endoglucanases, and esterases stable at low pH are known from various acidophilic microbes. The possibility of improving them by genetic engineering and directed evolution will further boost their industrial applications. Besides biocatalysts, other biomolecules such as plasmids, rusticynin, and maltose-bindingprotein have also been reported from acidophiles. Some strategies for circumventing the problems encountered in expressing genes encoding proteins from extreme acidophiles have been suggested. The investigations on the analysis of crystal structures of some acidophilic proteins have thrown light on their acid stability. Attempts are being made to use thermoacidophilic microbes for biofuelproduction from lignocellulosic

biomass. The enzymes from acidophiles are mainly used in polymer degradation. Keywords Acidophiles Á Biocatalysts Á Acid stable Á Extremophiles

Introduction Many microorganisms survive in the physically and geochemically extreme conditions, which challenge the physico-chemical limits of life like extremes of temperature, pH, salinity, pressure, desiccation, radiation,and others. These are termed as extremophiles. Among them, acidophiles are the organisms that thrive in acidic environments with pH less than 4.0. These are diverse group of organisms included in archaea, bacteria, fungi, algae, and protozoa growing in acidic conditions, reported from natural environments like solfataric fields, sulfuric pools and geysers, and artificial environments like areasassociated with human activities like mining of coal and metal ores. A few microbes belonging to the genera Acidithiobacillus and Sulfolobus generate acid through oxidation of sulfur. The species of Picrophilus, with optimum pH for growth of 0.7, are obligate acidophiles. Acidic water from mines and geothermal springs are dominated by heterotrophic bacteria belonging to the genera Acidiphilium andAlicyclobacillus having pH optima for growth between 2.5 and 6.0. While most of the extreme acidophiles belong to archaeal group that includes Acidianus, Desulphurolobus, Metallosphaera, Stygiolobus, Sulfolobus, Sulphurisphaera, Sufurococcus, Thermoplasma and Picrophilus (Bertoldo et al. 2004) (Table 1). To survive at extremes of pH, organisms require a networked cellular adaptation to surmountdifferent

Communicated by S. Albers. A. Sharma Á T. Satyanarayana (&) Department of Microbiology, University of Delhi South Campus, Benito Juarez Road, New Delhi 110021, India e-mail: tsnarayana@gmail.com Y. Kawarabayasi New Energy and Industrial Technology Development Organization (NEDO), 19F Muza Kawasaki Building, 1310 Omiya-cho, Saiwai-ku, Kawasaki, Kanagawa 212-8554, Japan

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2 Table 1The characteristics of acidophilic bacteria and archaea Organism Eubacteria Acidiphilium angustum Acidiphilium organovorum Acidiphilium symbioticum Acidiphilium aminolyticum Acidiphilium multivorum Acidiphilium cryptum Acidiphilium rubrum Acidiphilium facilis Acidimicrobium ferroxidans strain TH3 Alicyclobacillus acidocaldarius – 20–45 – 20–37 17–42 20–41 Mesophile – 30–55 45–70 – 37 37 – 27–35...