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Elizabeth L.j. Watkin - One of the best experts on this subject based on the ideXlab platform.
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Draft Genome Sequence of Acidihalobacter ferrooxidans DSM 14175 (Strain V8), a New Iron- and Sulfur-Oxidizing, Halotolerant, Acidophilic Species.
Genome Announcements, 2017Co-Authors: Himel N. Khaleque, Joshua P. Ramsay, Riley J. T. Murphy, Anna H. Kaksonen, Naomi J. Boxall, Elizabeth L.j. WatkinAbstract:ABSTRACT The use of halotolerant Acidophiles for bioleaching provides a biotechnical approach for the extraction of metals from regions where high salinity exists in the ores and source water. Here, we describe the first draft genome of a new species of a halotolerant and iron- and sulfur-oxidizing Acidophile, Acidihalobacter ferrooxidans DSM-14175 (strain V8).
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RNA transcript sequencing reveals inorganic sulfur compound oxidation pathways in the Acidophile Acidithiobacillus ferrivorans
FEMS Microbiology Letters, 2016Co-Authors: Stephan Christel, Elizabeth L.j. Watkin, Jimmy Fridlund, Antoine Buetti-dinh, Moritz Buck, Mark DopsonAbstract:Acidithiobacillus ferrivorans is an Acidophile implicated in low-temperature biomining for the recovery of metals from sulfide minerals. Acidithiobacillus ferrivorans obtains its energy from the ox ...
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Bioleaching in brackish waters--effect of chloride ions on the Acidophile population and proteomes of model species.
Applied Microbiology and Biotechnology, 2011Co-Authors: Carla M. Zammit, Mark Dopson, Stefanie Mangold, Venkateswara Rao Jonna, Lesley Mutch, Helen R. Watling, Elizabeth L.j. WatkinAbstract:High concentrations of chloride ions inhibit the growth of acidophilic microorganisms used in biomining, a problem particularly relevant to Western Australian and Chilean biomining operations. Despite this, little is known about the mechanisms Acidophiles adopt in order to tolerate high chloride ion concentrations. This study aimed to investigate the impact of increasing concentrations of chloride ions on the population dynamics of a mixed culture during pyrite bioleaching and apply proteomics to elucidate how two species from this mixed culture alter their proteomes under chloride stress. A mixture consisting of well-known biomining microorganisms and an enrichment culture obtained from an acidic saline drain were tested for their ability to bioleach pyrite in the presence of 0, 3.5, 7, and 20 g L−1 NaCl. Microorganisms from the enrichment culture were found to out-compete the known biomining microorganisms, independent of the chloride ion concentration. The proteomes of the Gram-positive Acidophile Acidimicrobium ferrooxidans and the Gram-negative Acidophile Acidithiobacillus caldus grown in the presence or absence of chloride ions were investigated. Analysis of differential expression showed that acidophilic microorganisms adopted several changes in their proteomes in the presence of chloride ions, suggesting the following strategies to combat the NaCl stress: adaptation of the cell membrane, the accumulation of amino acids possibly as a form of osmoprotectant, and the expression of a YceI family protein involved in acid and osmotic-related stress.
David S Holmes - One of the best experts on this subject based on the ideXlab platform.
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Effect of CO2 Concentration on Uptake and Assimilation of Inorganic Carbon in the Extreme Acidophile Acidithiobacillus ferrooxidans
Frontiers in Microbiology, 2019Co-Authors: Mario Esparza, Mark Dopson, Eugenia Jedlicki, Carolina González, David S HolmesAbstract:This study was motivated by surprising gaps in the current knowledge of microbial inorganic carbon (Ci) uptake and assimilation at acidic pH values (pH < 3). Particularly striking is the limited understanding of the differences between Ci uptake mechanisms in acidic versus circumneutral environments where the Ci predominantly occurs either as a dissolved gas (CO2) or as bicarbonate (HCO3-), respectively. In order to gain initial traction on the problem, the relative abundance of transcripts encoding proteins involved in Ci uptake and assimilation was studied in the autotrophic, polyextreme Acidophile Acidithiobacillus ferrooxidans whose optimum pH for growth is 2.5 using ferrous iron as an energy source, although they are able to grow at pH 5 when using sulfur as an energy source. The relative abundance of transcripts of five operons (cbb1-5) and one gene cluster (can-sulP) was monitored by RT-qPCR and, in selected cases, at the protein level by Western blotting, when cells were grown under different regimens of CO2 concentration in elemental sulfur. Of particular note was the absence of a classical bicarbonate uptake system in A. ferrooxidans. However, bioinformatic approaches predict that sulP, previously annotated as a sulfate transporter, is a novel type of bicarbonate transporter. A conceptual model of CO2 fixation was constructed from combined bioinformatic and experimental approaches that suggests strategies for providing ecological flexibility under changing concentrations of CO2 and provides a portal to elucidating Ci uptake and regulation in acidic conditions. The results could advance the understanding of industrial bioleaching processes to recover metals such as copper at acidic pH. In addition, they may also shed light on how chemolithoautotrophic Acidophiles influence the nutrient and energy balance in naturally occurring low pH environments.
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Data_Sheet_4_Effect of CO2 Concentration on Uptake and Assimilation of Inorganic Carbon in the Extreme Acidophile Acidithiobacillus ferrooxidans.PDF
2019Co-Authors: Mario Esparza, Mark Dopson, Eugenia Jedlicki, Carolina González, David S HolmesAbstract:This study was motivated by surprising gaps in the current knowledge of microbial inorganic carbon (Ci) uptake and assimilation at acidic pH values (pH < 3). Particularly striking is the limited understanding of the differences between Ci uptake mechanisms in acidic versus circumneutral environments where the Ci predominantly occurs either as a dissolved gas (CO2) or as bicarbonate (HCO3-), respectively. In order to gain initial traction on the problem, the relative abundance of transcripts encoding proteins involved in Ci uptake and assimilation was studied in the autotrophic, polyextreme Acidophile Acidithiobacillus ferrooxidans whose optimum pH for growth is 2.5 using ferrous iron as an energy source, although they are able to grow at pH 5 when using sulfur as an energy source. The relative abundance of transcripts of five operons (cbb1-5) and one gene cluster (can-sulP) was monitored by RT-qPCR and, in selected cases, at the protein level by Western blotting, when cells were grown under different regimens of CO2 concentration in elemental sulfur. Of particular note was the absence of a classical bicarbonate uptake system in A. ferrooxidans. However, bioinformatic approaches predict that sulP, previously annotated as a sulfate transporter, is a novel type of bicarbonate transporter. A conceptual model of CO2 fixation was constructed from combined bioinformatic and experimental approaches that suggests strategies for providing ecological flexibility under changing concentrations of CO2 and provides a portal to elucidating Ci uptake and regulation in acidic conditions. The results could advance the understanding of industrial bioleaching processes to recover metals such as copper at acidic pH. In addition, they may also shed light on how chemolithoautotrophic Acidophiles influence the nutrient and energy balance in naturally occurring low pH environments.
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Draft Genome Sequence of the Nominated Type Strain of “Ferrovum myxofaciens, ” an Acidophilic, Iron-Oxidizing Betaproteobacterium
2016Co-Authors: Ana Moya-beltrán, David S Holmes, Juan Pablo A Cárdenas, Paulo B C. Covarrubias, Francisco B Issotta, Francisco A J. Oss, Barry A M. Grail, Raquel B Quatrini, B Barrie D. JohnsoncAbstract:“Ferrovummyxofaciens ” is an iron-oxidizing betaproteobacterium with widespread distribution in acidic low-temperature en-vironments, such as acid mine drainage streams. Here, we describe the genomic features of this novel Acidophile and investigate the relevant metabolic pathways that enable its survival in these environments
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α-fur, an antisense RNA gene to fur in the extreme Acidophile Acidithiobacillus ferrooxidans
Microbiology, 2014Co-Authors: Claudia Lefimil, Eugenia Jedlicki, David S HolmesAbstract:A large non-coding RNA, termed α-Fur, of ~1000 nt has been detected in the extreme Acidophile Acidithiobacillus ferrooxidans encoded on the antisense strand to the iron-responsive master regulator fur (ferric uptake regulator) gene. A promoter for α-fur was predicted bioinformatically and validated using gene fusion experiments. The promoter is situated within the coding region and in the same sense as proB, potentially encoding a glutamate 5-kinase. The 3′ termination site of the α-fur transcript was determined by 3′ rapid amplification of cDNA ends to lie 7 nt downstream of the start of transcription of fur. Thus, α-fur is antisense to the complete coding region of fur, including its predicted ribosome-binding site. The genetic context of α-fur is conserved in several members of the genus Acidithiobacillus but not in all Acidophiles, indicating that it is monophyletic but not niche specific. It is hypothesized that α-Fur regulates the cellular level of Fur. This is the fourth example of an antisense RNA to fur, although it is the first in an extreme Acidophile, and underscores the growing importance of cis-encoded non-coding RNAs as potential regulators involved in the microbial iron-responsive stimulon.
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Metal resistance or tolerance? Acidophiles confront high metal loads via both abiotic and biotic mechanisms
Frontiers Media S.A., 2014Co-Authors: Mark Edopson, Francisco Eossandon, Lars Elövgren, David S HolmesAbstract:All metals are toxic at high concentrations and consequently their intracellular concentrations must be regulated. Acidophilic microorganisms have an optimum growth pH < 3 and proliferate in natural and anthropogenic low pH environments. Some Acidophiles are involved in the catalysis of sulfide mineral dissolution, resulting in high concentrations of metals in solution. Acidophiles are often described as highly metal resistant via mechanisms such as multiple and/or more efficient active resistance systems than are present in neutrophiles. However, this is not the case for all Acidophiles and we contend that their growth in high metal concentrations is partially due to an intrinsic tolerance as a consequence of the environment in which they live. In this perspective, we highlight metal tolerance via complexation of free metals by sulfate ions and passive tolerance to metal influx via an internal positive cytoplasmic transmembrane potential. These tolerance mechanisms have been largely ignored in past studies of Acidophile growth in the presence of metals and should be taken into account
Mark Dopson - One of the best experts on this subject based on the ideXlab platform.
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Effect of CO2 Concentration on Uptake and Assimilation of Inorganic Carbon in the Extreme Acidophile Acidithiobacillus ferrooxidans
Frontiers in Microbiology, 2019Co-Authors: Mario Esparza, Mark Dopson, Eugenia Jedlicki, Carolina González, David S HolmesAbstract:This study was motivated by surprising gaps in the current knowledge of microbial inorganic carbon (Ci) uptake and assimilation at acidic pH values (pH < 3). Particularly striking is the limited understanding of the differences between Ci uptake mechanisms in acidic versus circumneutral environments where the Ci predominantly occurs either as a dissolved gas (CO2) or as bicarbonate (HCO3-), respectively. In order to gain initial traction on the problem, the relative abundance of transcripts encoding proteins involved in Ci uptake and assimilation was studied in the autotrophic, polyextreme Acidophile Acidithiobacillus ferrooxidans whose optimum pH for growth is 2.5 using ferrous iron as an energy source, although they are able to grow at pH 5 when using sulfur as an energy source. The relative abundance of transcripts of five operons (cbb1-5) and one gene cluster (can-sulP) was monitored by RT-qPCR and, in selected cases, at the protein level by Western blotting, when cells were grown under different regimens of CO2 concentration in elemental sulfur. Of particular note was the absence of a classical bicarbonate uptake system in A. ferrooxidans. However, bioinformatic approaches predict that sulP, previously annotated as a sulfate transporter, is a novel type of bicarbonate transporter. A conceptual model of CO2 fixation was constructed from combined bioinformatic and experimental approaches that suggests strategies for providing ecological flexibility under changing concentrations of CO2 and provides a portal to elucidating Ci uptake and regulation in acidic conditions. The results could advance the understanding of industrial bioleaching processes to recover metals such as copper at acidic pH. In addition, they may also shed light on how chemolithoautotrophic Acidophiles influence the nutrient and energy balance in naturally occurring low pH environments.
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Data_Sheet_4_Effect of CO2 Concentration on Uptake and Assimilation of Inorganic Carbon in the Extreme Acidophile Acidithiobacillus ferrooxidans.PDF
2019Co-Authors: Mario Esparza, Mark Dopson, Eugenia Jedlicki, Carolina González, David S HolmesAbstract:This study was motivated by surprising gaps in the current knowledge of microbial inorganic carbon (Ci) uptake and assimilation at acidic pH values (pH < 3). Particularly striking is the limited understanding of the differences between Ci uptake mechanisms in acidic versus circumneutral environments where the Ci predominantly occurs either as a dissolved gas (CO2) or as bicarbonate (HCO3-), respectively. In order to gain initial traction on the problem, the relative abundance of transcripts encoding proteins involved in Ci uptake and assimilation was studied in the autotrophic, polyextreme Acidophile Acidithiobacillus ferrooxidans whose optimum pH for growth is 2.5 using ferrous iron as an energy source, although they are able to grow at pH 5 when using sulfur as an energy source. The relative abundance of transcripts of five operons (cbb1-5) and one gene cluster (can-sulP) was monitored by RT-qPCR and, in selected cases, at the protein level by Western blotting, when cells were grown under different regimens of CO2 concentration in elemental sulfur. Of particular note was the absence of a classical bicarbonate uptake system in A. ferrooxidans. However, bioinformatic approaches predict that sulP, previously annotated as a sulfate transporter, is a novel type of bicarbonate transporter. A conceptual model of CO2 fixation was constructed from combined bioinformatic and experimental approaches that suggests strategies for providing ecological flexibility under changing concentrations of CO2 and provides a portal to elucidating Ci uptake and regulation in acidic conditions. The results could advance the understanding of industrial bioleaching processes to recover metals such as copper at acidic pH. In addition, they may also shed light on how chemolithoautotrophic Acidophiles influence the nutrient and energy balance in naturally occurring low pH environments.
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RNA transcript sequencing reveals inorganic sulfur compound oxidation pathways in the Acidophile Acidithiobacillus ferrivorans
FEMS Microbiology Letters, 2016Co-Authors: Stephan Christel, Elizabeth L.j. Watkin, Jimmy Fridlund, Antoine Buetti-dinh, Moritz Buck, Mark DopsonAbstract:Acidithiobacillus ferrivorans is an Acidophile implicated in low-temperature biomining for the recovery of metals from sulfide minerals. Acidithiobacillus ferrivorans obtains its energy from the ox ...
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Architecture and gene repertoire of the flexible genome of the extreme Acidophile Acidithiobacillus caldus.
PLoS ONE, 2013Co-Authors: Lillian G. Acuña, Juan Pablo Cárdenas, Paulo C. Covarrubias, Amir Shmaryahu, Juan José Haristoy, Rodrigo Flores, Harold Nuñez, Gonzalo Riadi, Jorge Valdés, Mark DopsonAbstract:CITATION: Acuna, L. G. et al. 2013. Architecture and gene repertoire of the flexible genome of the extreme Acidophile Acidithiobacillus caldus. PLoS ONE, 8(11):e78237, doi:10.1371/journal.pone.0078237.
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Gene Identification and Substrate Regulation Provide Insights into Sulfur Accumulation during Bioleaching with the Psychrotolerant Acidophile Acidithiobacillus ferrivorans
Applied and Environmental Microbiology, 2012Co-Authors: Maria Liljeqvist, Olena Rzhepishevska, Mark DopsonAbstract:The psychrotolerant Acidophile Acidithiobacillus ferrivorans has been identified from cold environments and has been shown to use ferrous iron and inorganic sulfur compounds as its energy sources. A bioinformatic evaluation presented in this study suggested that Acidithiobacillus ferrivorans utilized a ferrous iron oxidation pathway similar to that of the related species Acidithiobacillus ferrooxidans. However, the inorganic sulfur oxidation pathway was less clear, since the Acidithiobacillus ferrivorans genome contained genes from both Acidithiobacillus ferrooxidans and Acidithiobacillus caldus encoding enzymes whose assigned functions are redundant. Transcriptional analysis revealed that the petA1 and petB1 genes (implicated in ferrous iron oxidation) were downregulated upon growth on the inorganic sulfur compound tetrathionate but were on average 10.5-fold upregulated in the presence of ferrous iron. In contrast, expression of cyoB1 (involved in inorganic sulfur compound oxidation) was decreased 6.6-fold upon growth on ferrous iron alone. Competition assays between ferrous iron and tetrathionate with Acidithiobacillus ferrivorans SS3 precultured on chalcopyrite mineral showed a preference for ferrous iron oxidation over tetrathionate oxidation. Also, pure and mixed cultures of psychrotolerant Acidophiles were utilized for the bioleaching of metal sulfide minerals in stirred tank reactors at 5 and 25°C in order to investigate the fate of ferrous iron and inorganic sulfur compounds. Solid sulfur accumulated in bioleaching cultures growing on a chalcopyrite concentrate. Sulfur accumulation halted mineral solubilization, but sulfur was oxidized after metal release had ceased. The data indicated that ferrous iron was preferentially oxidized during growth on chalcopyrite, a finding with important implications for biomining in cold environments.
Watkin Elizabeth - One of the best experts on this subject based on the ideXlab platform.
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Multiple osmotic stress responses in acidihalobacter prosperus result in tolerance to chloride ions
'Frontiers Media SA', 2017Co-Authors: Dopson M., Holmes D., Lazcano M., Mccredden T., Bryan C., Mulroney K., Steuart R., Jackaman Connie, Watkin ElizabethAbstract:Extremely acidophilic microorganisms (pH optima for growth of =3) are utilized for the extraction of metals from sulfide minerals in the industrial biotechnology of "biomining." A long term goal for biomining has been development of microbial consortia able to withstand increased chloride concentrations for use in regions where freshwater is scarce. However, when challenged by elevated salt, Acidophiles experience both osmotic stress and an acidification of the cytoplasm due to a collapse of the inside positive membrane potential, leading to an influx of protons. In this study, we tested the ability of the halotolerant Acidophile Acidihalobacter prosperus to grow and catalyze sulfide mineral dissolution in elevated concentrations of salt and identified chloride tolerance mechanisms in Ac. prosperus as well as the chloride susceptible species, Acidithiobacillus ferrooxidans. Ac. prosperus had optimum iron oxidation at 20 g L-1 NaCl while At. ferrooxidans iron oxidation was inhibited in the presence of 6 g L-1 NaCl. The tolerance to chloride in Ac. prosperus was consistent with electron microscopy, determination of cell viability, and bioleaching capability. The Ac. prosperus proteomic response to elevated chloride concentrations included the production of osmotic stress regulators that potentially induced production of the compatible solute, ectoine uptake protein, and increased iron oxidation resulting in heightened electron flow to drive proton export by the F0F1 ATPase. In contrast, At. ferrooxidans responded to low levels of Cl- with a generalized stress response, decreased iron oxidation, and an increase in central carbon metabolism. One potential adaptation to high chloride in the Ac. prosperus Rus protein involved in ferrous iron oxidation was an increase in the negativity of the surface potential of Rus Form I (and Form II) that could help explain how it can be active under elevated chloride concentrations. These data have been used to create a model of chloride tolerance in the salt tolerant and susceptible species Ac. prosperus and At. ferrooxidans, respectively. © 2017 The Authors
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Draft Genome Sequence of the Acidophilic, Halotolerant, and Iron/Sulfur-Oxidizing Acidihalobacter prosperus DSM 14174 (Strain V6).
'American Society for Microbiology', 2017Co-Authors: Khaleque H., Murphy R., Kaksonen A., Boxall N., Ramsay J., Watkin ElizabethAbstract:The principal genomic features of Acidihalobacter prosperus DSM 14174 (strain V6) are presented here. This is a mesophilic, halotolerant, and iron/sulfur-oxidizing Acidophile that was isolated from seawater at Vulcano, Italy. It has potential for use in biomining applications in regions where high salinity exists in the source water and ores
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Draft Genome Sequence of the Iron-Oxidizing, Acidophilic, and Halotolerant “Thiobacillus prosperus” Type Strain DSM 5130
'American Society for Microbiology', 2014Co-Authors: Ossandon F., Holmes D., Cardenas J., Corbett Melissa, Quatrini R., Watkin ElizabethAbstract:“Thiobacillus prosperus” is a halotolerant mesophilic Acidophile that gains energy through iron and sulfur oxidation. Its physiology is poorly understood. Here, we describe the principal genomic features of the type strain of T. prosperus, DSM 5130. This is the first public genome sequence of an acidophilic halotolerant bacterium
Barrie D. Johnson - One of the best experts on this subject based on the ideXlab platform.
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Acidophile microbiology in space and time
Current Issues in Molecular Biology, 2020Co-Authors: Barrie D. Johnson, Raquel QuatriniAbstract:The study of extreme Acidophiles, broadly defined as microorganisms that grow optimally at pH values below 3, was initiated by the discovery by Waksman and Joffe in the early 1900s of a bacterium that was able to live in the dilute sulfuric acid it generated by oxidizing elemental sulfur. The number of known Acidophiles remained relatively small until the second half of the 20th century, but since then has greatly expanded to include representatives of living organisms from within all three domains of life on earth, and notably within many of the major divisions and phyla of Bacteria and Archaea. Environments that are naturally acidic are found throughout the world, and others that are man-made (principally from mining metals and coal) are also widely distributed. These continue to be sites for isolating new species, (and sometimes new genera) which thrive in acidic liquor solutions that contain concentrations of metals and metalloids that are lethal to most life forms. The development and application of molecular techniques and, more recently, next generation sequencing technologies has, as with other areas of biology, revolutionized the study of Acidophile microbiology. Not only have these studies provided greater understanding of the diversity of organisms present in extreme acidic environments and aided in the discovery of largely overlooked taxa (such as the ultra-small uncultivated archaea), but have also helped uncover some of the unique adaptations of life forms that live in extremely acidic environments. Thanks to the relatively low biological complexity of these ecosystems, systems-level spatio-temporal studies of model communities have been achieved, laying the foundations for 'multi-omic' exploration of other ecosystems. This article introduces the subject of Acidophile microbiology, tracing its origins to the current status quo, and provides the reader with general information which provides a backdrop to the more specific topics described in Quatrini and Johnson (2016).
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Recent Advances in Acidophile Microbiology: Fundamentals and Applications
Frontiers Media SA, 2017Co-Authors: Axel Schippers, Barrie D. JohnsonAbstract:There is considerable interest in pure and applied studies of extremophilic microorganisms, including those (Acidophiles) that are active in low pH environments. As elsewhere in microbiology, this is a fast-developing field, and the proposed special issue of Frontiers highlights many of the more recent advances that have been made in this area. Authors from leading scientific groups located in North and South America, Australasia and Europe have contributed to this e-book, and the topics covered include advances in molecular, biochemical, biogeochemical and industrial aspects of Acidophile microbiology
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Iron Kinetics and Evolution of Microbial Populations in Low-pH, Ferrous Iron-Oxidizing Bioreactors
2016Co-Authors: Rose M. Jones, Barrie D. JohnsonAbstract:Iron-rich, acidic wastewaters are commonplace pollutants associated with metal and coal mining. Continuous-flow bioreactors were commissioned and tested for their capacities to oxidize ferrous iron in synthetic and actual acid mine drainage waters using (initially) pure cultures of the recently described acidophilic, iron-oxidizing heterotrophic bacterium Acidithrix ferrooxidans grown in the presence of glucose and yeast extract. The bioreactors became rapidly colonized by this bacterium, which formed macroscopic streamer growths in the flowing waters. Over 97% of ferrous iron in pH 2.0–2.2 synthetic mine water was oxidized (at up to 225 mg L–1 h–1) at dilution rates (D) of 0.6 h–1. Rates of iron oxidation decreased with pH but were still significant, with influent liquors as low as pH 1.37. When fed with actual mine water, >90% of ferrous iron was oxidized at D values of 0.4 h–1, and microbial communities within the bioreactors changed over time, with Atx. ferrooxidans becoming increasingly displaced by the autotrophic iron-oxidizing Acidophiles Ferrovum myxofaciens, Acidithiobacillus ferrivorans, and Leptospirillum ferrooxidans (which were all indigenous to the mine water), although this did not have a negative impact on net ferrous-iron oxidation. The results confirmed the potential of using a heterotrophic Acidophile to facilitate the rapid commissioning of iron-oxidizing bioreactors and illustrated how microbial communities within them can evolve without compromising the performances of the bioreactors
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reductive dissolution of minerals and selective recovery of metals using acidophilic iron and sulfate reducing Acidophiles
Hydrometallurgy, 2012Co-Authors: Barrie D. JohnsonAbstract:Abstract Most microbiological applications in biohydrometallurgy use the abilities of some acidophilic bacteria and archaea to catalyze oxidative transformations of metals (e.g. iron) and non-metals (e.g. sulfur), and thereby either to facilitate metal extraction and recovery (bioleaching and bio-oxidation), or to immobilize metals and metalloids (iron, arsenic etc.) in bioremediation of mine wastes. Many Acidophiles, including species more well known as iron- and sulfur-oxidizers, can also catalyze reductive transformations of these elements in anoxic or micro-aerobic environments, though the biotechnological potential of the latter has, for the most part, been ignored. Three potential applications of iron- and sulfate-reduction mediated by acidophilic bacteria are described in this review. The first of these uses the chemolithotroph Acidithiobacillus ferrooxidans to accelerate the dissolution of ferric iron oxy-hydroxides by coupling the oxidation of elemental sulfur to iron reduction when, grown under anaerobic conditions. This is the key reaction in the “ Ferredox ” process for extracting nickel from lateritic ores. Secondly, a continuous flow ferrous iron-generating bioreactor is described in which the heterotrophic Acidophile Acidiphilium SJH, immobilized on porous beads, is used to couple the oxidation of glycerol to the reduction of soluble ferric iron in feed liquors. Iron-reducing bioreactors have potential both in mineral bio-processing (e.g. indirect leaching of oxidized ores) and mine water remediation. A laboratory-scale (2 L) reactor was demonstrated to reduce between 90 and 99.9% of ferric iron at dilution rates of up to 0.87 h − 1 , with ~ 1 g of ferric iron being reduced h − 1 at the highest flow rates. The heterotrophic iron-reducing system also has the advantage of not requiring anoxic conditions to operate efficiently. Thirdly, selective precipitation of copper and zinc from synthetic mine waters containing a variety of soluble metals has been demonstrated in anaerobic bioreactors, operated at pH 2.2–3.8, using novel consortia of acidophilic sulfate-reducing bacteria. Environmentally-benign technologies for remediating acid mine and process waters, using controlled biosulfidogenesis in acidic liquors to ameliorate pH and to recover dissolved metals, have many advantages over conventional remediation strategies.