The iron-oxidizing proteobacteria HEDRICH, Sabrina; SCHLÖMANN, Michael; JOHNSON, D. Barrie
Microbiology,
06/2011, Letnik:
157, Številka:
Pt 6
Journal Article
Recenzirano
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The 'iron bacteria' are a collection of morphologically and phylogenetically heterogeneous prokaryotes. They include some of the first micro-organisms to be observed and described, and continue to be ...the subject of a considerable body of fundamental and applied microbiological research. While species of iron-oxidizing bacteria can be found in many different phyla, most are affiliated with the Proteobacteria. The latter can be subdivided into four main physiological groups: (i) acidophilic, aerobic iron oxidizers; (ii) neutrophilic, aerobic iron oxidizers; (iii) neutrophilic, anaerobic (nitrate-dependent) iron oxidizers; and (iv) anaerobic photosynthetic iron oxidizers. Some species (mostly acidophiles) can reduce ferric iron as well as oxidize ferrous iron, depending on prevailing environmental conditions. This review describes what is currently known about the phylogenetic and physiological diversity of the iron-oxidizing proteobacteria, their significance in the environment (on the global and micro scales), and their increasing importance in biotechnology.
Acidithiobacillus ferrooxidans Quatrini, Raquel; Johnson, D. Barrie
Trends in microbiology (Regular ed.),
March 2019, 2019-03-00, 20190301, Letnik:
27, Številka:
3
Journal Article
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Acidithiobacillus ferrooxidans is by far the most widely studied of all extremely acidophilic prokaryotes. While it is found in many types of natural low-pH environments in a variety ...of geoclimatic contexts, it has been more widely cited in anthropogenic (mostly mine-impacted) environments. It is responsible for accelerating the oxidative dissolution of sulfide minerals, causing the generation of polluting acidic metal-rich drainage waters but also facilitating the recovery of base and precious metals from mineral leachates. It can colonize barren mineral landscapes, is a driver of ecological successions in acidic biotopes, and is an important model organism in astrobiology. It catalyses the dissimilatory oxidation of iron, sulfur, and hydrogen, and the reduction of iron and sulfur, and has a major impact in the geochemical cycling of these elements in low-pH environments. This infographic summarizes the fundamental phylogeny, physiology and genomic features of this extremophile.
•Acidic microbiomes are tractable model systems in biogeochemical cycling studies.•Their spatial diversity patterns have been resolved at several different scales.•The main physico-chemical drivers ...of their diversity patterns have been uncovered.•Advances anticipate new opportunities to synthetically engineer relevant interactions.
Extremely acidic environments have global distribution and can have natural or, increasingly, anthropogenic origins. Extreme acidophiles grow optimally at pH 3 or less, have multiple strategies for tolerating stresses that accompany high levels of acidity and are scattered in all three domains of the tree of life. Metagenomic studies have expanded knowledge of the diversity of extreme acidophile communities, their ecological networks and their metabolic potentials, both confirmed and inferred. High resolution compositional and functional profiling of these microbiomes have begun to reveal spatial diversity patterns at global, regional, local, zonal and micro-scales. Future integration of genomic and other meta-omic data will offer new opportunities to utilize acidic microbiomes and to engineer beneficial interactions within them in biotechnologies.
The genus Acidithiobacillus includes three species that conserve energy from the oxidation of ferrous iron, as well as reduced sulfur, to support their growth. Previous work, based on multi-locus ...sequence analysis, identified a fourth group of iron- and sulfur-oxidizing acidithiobacilli as a potential distinct species. Eleven strains of 'Group IV' acidithiobacilli, isolated from different global locations, have been studied. These were all shown to be obligate chemolithotrophs, growing aerobically by coupling the oxidation of ferrous iron or reduced sulfur (but not hydrogen) to molecular oxygen, or anaerobically by the oxidation of reduced sulfur coupled to ferric iron reduction. All strains were mesophilic, although some were also psychrotolerant. Strain variation was also noted in terms of tolerance to extremely low pH and to elevated concentrations of transition metals. One strain was noted to display far greater tolerance to chloride than reported for other iron-oxidizing acidithiobacilli. All of the strains were able to catalyse the oxidative dissolution of pyrite and, on the basis of some of the combined traits of some of the strains examined, it is proposed that these may have niche roles in commercial mineral bioprocessing operations, such as for low temperature bioleaching of polysulfide ores in brackish waters. The name Acidithiobacillus ferriphilus sp. nov. is proposed to accommodate the strains described, with the type strain being M20T ( = DSM 100412T = JCM 30830T).
Mine waters are widely regarded as environmental pollutants, but are also potential sources of valuable metals. Water draining the Maurliden mine (Sweden) is highly acidic (pH 2.3) and rich in zinc ...(∼460 mg L–1) and iron (∼400 mg L–1), and contains smaller concentrations (0.3–49 mg L–1) of other transition metals and arsenic. We have developed novel techniques that promote the concurrent amelioration of acidic waste waters and selective recovery of metals, and have used these systems to treat synthetic Maurliden mine water in the laboratory. The two major metals present were removed via controlled biomineralization: zinc as ZnS in a sulfidogenic bioreactor, and iron as schwertmannite by microbial iron oxidation and precipitation of ferric iron. A small proportion (∼11%) of the schwertmannite produced was used to remove arsenic as the initial step in the process, and other chalcophilic metals (copper, cadmium and cobalt) were removed (as sulfides) in the stage 1 metal sulfide precipitation reactor. Results from this work have demonstrated that modular biomineralization units can be effective at processing complex mine waters and generating metal products that may be recycled. The economic and environmental benefits of using an integrated biological approach for treating metal-rich mine waters is discussed.
Summary
Extremely acidic, sulfur‐rich environments can be natural, such as solfatara fields in geothermal and volcanic areas, or anthropogenic, such as acid mine drainage waters. Many species of ...acidophilic bacteria and archaea are known to be involved in redox transformations of sulfur, using elemental sulfur and inorganic sulfur compounds as electron donors or acceptors in reactions involving between one and eight electrons. This minireview describes the nature and origins of acidic, sulfur‐rich environments, the biodiversity of sulfur‐metabolizing acidophiles, and how sulfur is metabolized and assimilated by acidophiles under aerobic and anaerobic conditions. Finally, existing and developing technologies that harness the abilities of sulfur‐oxidizing and sulfate‐reducing acidophiles to extract and capture metals, and to remediate sulfur‐polluted waste waters are outlined.
Twelve strains of iron-oxidizing acidithiobacilli isolated from acidic sites throughout the world, including some previously shown by multi-locus sequence analyses and DNA–DNA hybridization to ...comprise a distinct species, were characterized in terms of their physiologies. The bacteria were shown to be obligately chemolithotrophic, acidophilic and mesophilic, and grew in both oxic and anoxic environments, using ferrous iron, reduced sulfur or hydrogen as electron donors and oxygen or ferric iron as electron acceptors. Some of the strains grew at lower pH than those reported for the two recognized iron-oxidizing Acidithiobacillus species, Acidithiobacillus ferrooxidans and Acidithiobacillus ferrivorans. Tolerance of transition metals and aluminium, and also specific rates of iron oxidation and reduction, were more similar to those of A. ferrooxidans (to which the strains are more closely related) than to A. ferrivorans. The name Acidithiobacillus ferridurans sp. nov. is proposed to accommodate the 12 strains, with the type strain being JCM 18981T ( = ATCC 33020T).
Many different species of acidophilic prokaryotes, widely distributed within the domains Bacteria and Archaea, can catalyze the dissimilatory oxidation of ferrous iron or reduction of ferric iron, or ...can do both. Microbially mediated cycling of iron in extremely acidic environments (pH < 3) is strongly influenced by the enhanced chemical stability of ferrous iron and far greater solubility of ferric iron under such conditions. Cycling of iron has been demonstrated in vitro using both pure and mixed cultures of acidophiles, and there is considerable evidence that active cycling of iron occurs in acid mine drainage streams, pit lakes, and iron-rich acidic rivers, such as the Rio Tinto. Measurements of specific rates of iron oxidation and reduction by acidophilic microorganisms show that different species vary in their capacities for iron oxido-reduction, and that this is influenced by the electron donor provided and growth conditions used. These measurements, and comparison with corresponding data for oxidation of reduced sulfur compounds, also help explain why ferrous iron is usually used preferentially as an electron donor by acidophiles that can oxidize both iron and sulfur, even though the energy yield from oxidizing iron is much smaller than that available from sulfur oxidation. Iron-oxidizing acidophiles have been used in biomining (a technology that harness their abilities to accelerate the oxidative dissolution of sulfidic minerals and thereby facilitate the extraction of precious and base metals) for several decades. More recently they have also been used to simultaneously remediate iron-contaminated surface and ground waters and produce a useful mineral by-product (schwertmannite). Bioprocessing of oxidized mineral ores using acidophiles that catalyze the reductive dissolution of ferric iron minerals such as goethite has also recently been demonstrated, and new biomining technologies based on this approach are being developed.
Abstract
While many prokaryotic species are known to use hydrogen as an electron donor to support their growth, this trait has only previously been reported for two acidophilic bacteria, ...Hydrogenobaculum acidophilum (in the presence of reduced sulfur) and Acidithiobacillus (At.) ferrooxidans. To test the hypothesis that hydrogen may be utilized more widely by acidophilic bacteria, 38 strains of acidophilic bacteria, including representatives of 20 designated and four proposed species, were screened for their abilities to grow via the dissimilatory oxidation of hydrogen. Growth was demonstrated in several species of acidophiles that also use other inorganic electron donors (ferrous iron and sulfur) but in none of the obligately heterotrophic species tested. Strains of At. ferrooxidans, At. ferridurans and At. caldus, grew chemolithotrophically on hydrogen, though those of At. thiooxidans and At. ferrivorans did not. Growth was also observed with Sulfobacillus acidophilus, Sb. benefaciens and Sb. thermosulfidooxidans, though not with other iron-oxidizing Firmicutes. Similarly, Acidimicrobium ferrooxidans grew on hydrogen, closely related acidophilic actinobacteria did not. Growth yields of At. ferrooxidans and At. ferridurans grown aerobically on hydrogen (c. 1010 cells mL−1) were far greater than typically obtained using other electron donors. Several species also grew anaerobically by coupling hydrogen oxidation to the reduction of ferric iron.
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