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Category: Environmental Microbiology
The Microbiology of Extremely Acidic Environments, Page 1 of 2
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Extremely acidic environments, defined having a pH of <3, are found in locations as diverse as the Arctic and the Tropics. While these be natural phenomena, human activity, most notoriously mining of metals and coals, are often responsible for the severe acidification of localized environments. The indigenous microflora in extremely acidic environments include species of prokaryotes and eukaryotes, many of which are obligately acidophilic. Acidophiles are widely distributed throughout the "tree of life", and include species of Bacteria, Archaea and Eukarya that are often only very distantly related to each other. Various mechanisms are used by acidophiles to adapt to the challenges they face, which include contending with elevated concentrations of transition metals and metalloids, and severely limited bioavailability of macronutrients such as phosphate.
Inorganic energy sources (reduced iron and sulfur) are highly abundant in many extremely acidic environments. Chemolithotrophic acidophiles are the basis of food webs in subterranean and also contribute to net primary production in deep submarine geothermal vents. However, where solar energy is available phototrophic acidophiles, predominantly species of acidophilic eukaryotic microalgae, proliferate and assume the dominant role of primary producers. Acidophilic microorganisms interact with each other in various ways, including via redox transformations of iron and sulfur, generating electron donors and acceptors for prokaryotic metabolisms, and via provision of organic compounds (supporting heterotrophic species) or inorganic carbon (supporting autotrophs). Acidophiles have long been used to extract metals from ores (biomining) and biotechnologies are emerging that harness their abilities to remediate polluted waters and recover metals.
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Acidic environments at geothermal sites: (a) Norris geyser basin, Yellowstone National Park, WY; (b) a hot spring on São Miguel, Azores; (c) prismatic sulfur crystals forming in a volcanic vent, Montserrat, WI. doi:10.1128/9781555818821.ch4.3.1.f1
Acidic environments at geothermal sites: (a) Norris geyser basin, Yellowstone National Park, WY; (b) a hot spring on São Miguel, Azores; (c) prismatic sulfur crystals forming in a volcanic vent, Montserrat, WI. doi:10.1128/9781555818821.ch4.3.1.f1
Simplified representation of ferrous iron oxidation by the iron-oxidizing acidithiobacilli protons entering the cytoplasm via the membrane-bound ATP synthetase complex (ATPase, shown in purple) are counterbalanced by electrons that derive from the oxidation of ferrous iron, mediated by cytochromes and rusticyanin (shown in green and yellow) located in the acidic periplasm. Cytochrome oxidase (shown in blue) catalyzes the reduction of molecular oxygen by incoming protons and electrons, generating water, the sole metabolic end product of this process.
doi:10.1128/9781555818821.ch4.3.1.f2
Simplified representation of ferrous iron oxidation by the iron-oxidizing acidithiobacilli protons entering the cytoplasm via the membrane-bound ATP synthetase complex (ATPase, shown in purple) are counterbalanced by electrons that derive from the oxidation of ferrous iron, mediated by cytochromes and rusticyanin (shown in green and yellow) located in the acidic periplasm. Cytochrome oxidase (shown in blue) catalyzes the reduction of molecular oxygen by incoming protons and electrons, generating water, the sole metabolic end product of this process.
doi:10.1128/9781555818821.ch4.3.1.f2
Microbial eukaryotic biofilms found in the Río Tinto: (a) green filaments formed mainly by Zygnemopsis and Klebsormidium; (b) biofilms of Chlamydomonas sp.; (c) biofilms formed mostly by euglenoids and diatoms; biofilms of Galdieria sp. The scale bars represent 5 cm. doi:10.1128/9781555818821.ch4.3.1.f3
Microbial eukaryotic biofilms found in the Río Tinto: (a) green filaments formed mainly by Zygnemopsis and Klebsormidium; (b) biofilms of Chlamydomonas sp.; (c) biofilms formed mostly by euglenoids and diatoms; biofilms of Galdieria sp. The scale bars represent 5 cm. doi:10.1128/9781555818821.ch4.3.1.f3
Light micrographs of different eukaryotic species isolated from the Río Tinto: (a) Klebsormidium sp. (filamentous green algae); (b) Actinophrys sp. (Heliozoa); (c) Galdieria sp. (red algae); (d) Euglena mutabilis; (e) amoebae (protoctista); (f) Chlamydomonas sp. (green algae). The scale bar represents 10 μm. doi:10.1128/9781555818821.ch4.3.1f4
Light micrographs of different eukaryotic species isolated from the Río Tinto: (a) Klebsormidium sp. (filamentous green algae); (b) Actinophrys sp. (Heliozoa); (c) Galdieria sp. (red algae); (d) Euglena mutabilis; (e) amoebae (protoctista); (f) Chlamydomonas sp. (green algae). The scale bar represents 10 μm. doi:10.1128/9781555818821.ch4.3.1f4
(Top): schematic representation of the “overlay” technique for isolating and enumerating different physiological groups of acidophilic prokaryotes. A two-layered gel is prepared, with the underlay being inoculated either with a strain (e.g., SJH) of A. cryptum (to cultivate autotrophic acidophiles), or Ac. aromatica (to cultivate heterotrophic acidophiles, as this acidophile “detoxifies” the medium but does not use organic compounds such as glycerol and yeast extract which are used by most other acidophilic heterotrophs). (Bottom): (a) colonies of iron-oxidizing acidophiles, isolated from the Río Tinto on ferrous iron overlay plates; (b) colonies of heterotrophic acidophiles, isolated from an abandoned copper mine (Roeros) in Norway on yeast extract–containing overlay plates. doi:10.1128/9781555818821.ch4.3.1.f5
(Top): schematic representation of the “overlay” technique for isolating and enumerating different physiological groups of acidophilic prokaryotes. A two-layered gel is prepared, with the underlay being inoculated either with a strain (e.g., SJH) of A. cryptum (to cultivate autotrophic acidophiles), or Ac. aromatica (to cultivate heterotrophic acidophiles, as this acidophile “detoxifies” the medium but does not use organic compounds such as glycerol and yeast extract which are used by most other acidophilic heterotrophs). (Bottom): (a) colonies of iron-oxidizing acidophiles, isolated from the Río Tinto on ferrous iron overlay plates; (b) colonies of heterotrophic acidophiles, isolated from an abandoned copper mine (Roeros) in Norway on yeast extract–containing overlay plates. doi:10.1128/9781555818821.ch4.3.1.f5
(a) the Río Tinto in the Iberian Peninsula Belt, Spain; (b) a pit lake in the abandoned São Domingos copper mine, Portugal. doi:10.1128/9781555818821.ch4.3.1.f6
(a) the Río Tinto in the Iberian Peninsula Belt, Spain; (b) a pit lake in the abandoned São Domingos copper mine, Portugal. doi:10.1128/9781555818821.ch4.3.1.f6
Microbial growth and geochemical transformations of iron, sulfur, and carbon in an acidic (pH 2.5) stream draining a small abandoned copper mine (Cantareras) in the Iberian Pyrite Belt. Algal surface streamers overlie a bacterial mat that is light brown in color (and populated by iron-reducing acidophiles) which in turn overlies a charcoal-colored mat, which contains sulfate-reducing and other heterotrophic acidophiles. Most fixation of inorganic carbon in the stream community is mediated by acidophilic algae, though autotrophic iron- and sulfur-oxidizing bacteria also contribute to net primary production. doi:10.1128/9781555818821.ch4.3.1.f7
Microbial growth and geochemical transformations of iron, sulfur, and carbon in an acidic (pH 2.5) stream draining a small abandoned copper mine (Cantareras) in the Iberian Pyrite Belt. Algal surface streamers overlie a bacterial mat that is light brown in color (and populated by iron-reducing acidophiles) which in turn overlies a charcoal-colored mat, which contains sulfate-reducing and other heterotrophic acidophiles. Most fixation of inorganic carbon in the stream community is mediated by acidophilic algae, though autotrophic iron- and sulfur-oxidizing bacteria also contribute to net primary production. doi:10.1128/9781555818821.ch4.3.1.f7
Comparison of free energy changes associated with the oxidation of electron donors used by acidophilic prokaryotes ( 91 )
Comparison of free energy changes associated with the oxidation of electron donors used by acidophilic prokaryotes ( 91 )
Contrasting physiological properties of Acidithiobacillus spp. a
Contrasting physiological properties of Acidithiobacillus spp. a
Physiological properties of acidophilic actinobacteria
Physiological properties of acidophilic actinobacteria