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Growth and survival of Acidithiobacilli in Acidic, metal rich environments
Umeå University, Faculty of Science and Technology, Department of Molecular Biology (Faculty of Science and Technology). (Mark Dopson)
2012 (English)Doctoral thesis, comprehensive summary (Other academic)Alternative title
Tillväxt och överlevnad av Acidithiobacilli i sura, metallrika miljöer (Swedish)
Abstract [en]

Acidithiobacilli are acidophilic microorganisms that play important roles in many natural processes such as acidification of the environment, influencing metal mobility, and impacting on global sulfur and iron cycles. Due to their distinct metabolic properties they can be applied in the industrial extraction of valuable metals. Acidithiobacilli thrive in an environment which is extremely acidic and usually low in organic carbon but highly polluted with metals. In the quest to gain insight into how these microorganisms can thrive in their extreme environment, relevant facets of metabolism, metal resistance, and pH homeostasis were exploredwith the focus on two model organisms,

Acidithiobacillus caldus and Acidithiobacillus ferrooxidans. Understanding these fundamental aspects of an acidophilic lifestyle will help to eventually control detrimental effects on the environment due to acidification and metal pollution as well as improving metal extraction utilizing acidophilic microorganisms.

Bioinformatics can give information about the genetic capacity of an organism. Likewise, ‘omics’ techniques, such as transcriptomics and proteomics to study gene transcription profiles and differentially expressed proteins canyield insights into general responses as well as giving clues regarding specific mechanisms for adaptation to life in extreme environments. This approach was used to investigate the sulfur metabolism of

At. caldus which is an important sulfur oxidizer for industrial metal extraction. It was found that sulfur oxidation pathways were diverse within acidithiobacilli and a model of At. caldus sulfur oxidation was proposed. Furthermore, At. ferrooxidans anaerobic sulfur oxidation coupled to ferric iron reduction was studied which can be of importance for industrial processes. It was shown that anaerobic sulfur oxidation was, at least in part, indirectly coupled to ferric iron reduction via sulfide generation. Moreover, metal toxicity and resistance mechanisms in acidophiles are of major interest. Thus, zinc toxicity in three model organisms, At. caldus, Acidimicrobium ferrooxidans, and ‘Ferroplasma acidarmanus’, was explored. An important finding was that the speciation of metals and other chemical influences were of great importance for zinc toxicity in acidophiles. Additionally, the three organisms showed distinct responses to elevated zinc levels. Finally, the response of At. caldus to various suboptimal growth pH was evaluated to gain insights into pH homeostasis mechanisms. The results indicated that At. caldus used acid resistance mechanisms similar to those described for neutrophilic microorganisms. Analysis of fatty acid profiles demonstrated an active modulation of the cyctoplasmic membrane in response to proton concentration, likely resulting in a more rigid membrane at lower pH.

Place, publisher, year, edition, pages
Umeå: Umeå Universitet , 2012. , 70 p.
National Category
Microbiology
Identifiers
URN: urn:nbn:se:umu:diva-60439ISBN: 978-91-7459-474-4 (print)OAI: oai:DiVA.org:umu-60439DiVA: diva2:562081
Public defence
2012-11-23, NUS - Norrlands universitetssjukhus, 933 Unod B9, Norrlands universitetssjukhus, Umeå, 09:00
Opponent
Supervisors
Available from: 2012-11-02 Created: 2012-10-11 Last updated: 2012-10-23Bibliographically approved
List of papers
1. Sulfur metabolism in the extreme acidophile acidithiobacillus caldus
Open this publication in new window or tab >>Sulfur metabolism in the extreme acidophile acidithiobacillus caldus
2011 (English)In: Frontiers in microbiology, ISSN 1664-302X, Vol. 2, 17- p.Article in journal (Refereed) Published
Abstract [en]

Given the challenges to life at low pH, an analysis of inorganic sulfur compound (ISC) oxidation was initiated in the chemolithoautotrophic extremophile Acidithiobacillus caldus. A. caldus is able to metabolize elemental sulfur and a broad range of ISCs. It has been implicated in the production of environmentally damaging acidic solutions as well as participating in industrial bioleaching operations where it forms part of microbial consortia used for the recovery of metal ions. Based upon the recently published A. caldus type strain genome sequence, a bioinformatic reconstruction of elemental sulfur and ISC metabolism predicted genes included: sulfide-quinone reductase (sqr), tetrathionate hydrolase (tth), two sox gene clusters potentially involved in thiosulfate oxidation (soxABXYZ), sulfur oxygenase reductase (sor), and various electron transport components. RNA transcript profiles by semi quantitative reverse transcription PCR suggested up-regulation of sox genes in the presence of tetrathionate. Extensive gel based proteomic comparisons of total soluble and membrane enriched protein fractions during growth on elemental sulfur and tetrathionate identified differential protein levels from the two Sox clusters as well as several chaperone and stress proteins up-regulated in the presence of elemental sulfur. Proteomics results also suggested the involvement of heterodisulfide reductase (HdrABC) in A. caldus ISC metabolism. A putative new function of Hdr in acidophiles is discussed. Additional proteomic analysis evaluated protein expression differences between cells grown attached to solid, elemental sulfur versus planktonic cells. This study has provided insights into sulfur metabolism of this acidophilic chemolithotroph and gene expression during attachment to solid elemental sulfur.

Place, publisher, year, edition, pages
Frontiers Media, 2011
National Category
Natural Sciences
Identifiers
urn:nbn:se:umu:diva-56532 (URN)10.3389/fmicb.2011.00017 (DOI)21687411 (PubMedID)
Available from: 2012-06-20 Created: 2012-06-20 Last updated: 2012-10-23Bibliographically approved
2. Anaerobic Sulfur Metabolism Coupled to Dissimilatory Iron Reduction in the Extremophile Acidithiobacillus ferrooxidans
Open this publication in new window or tab >>Anaerobic Sulfur Metabolism Coupled to Dissimilatory Iron Reduction in the Extremophile Acidithiobacillus ferrooxidans
Show others...
2013 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 79, no 7, 2172-2181 p.Article in journal (Refereed) Published
Abstract [en]

Gene transcription (microarrays) and protein levels (proteomics) were compared in cultures of the acidophilic chemolithotroph Acidithiobacillus ferrooxidans grown on elemental sulfur as the electron donor under aerobic and anaerobic conditions, using either molecular oxygen or ferric iron as the electron acceptor, respectively. No evidence supporting the role of either tetrathionate hydrolase or arsenic reductase in mediating the transfer of electrons to ferric iron (as suggested by previous studies) was obtained. In addition, no novel ferric iron reductase was identified. However, data suggested that sulfur was disproportionated under anaerobic conditions, forming hydrogen sulfide via sulfur reductase and sulfate via heterodisulfide reductase and ATP sulfurylase. Supporting physiological evidence for H2S production came from the observation that soluble Cu2+ included in anaerobically incubated cultures was precipitated (seemingly as CuS). Since H2S reduces ferric iron to ferrous in acidic medium, its production under anaerobic conditions indicates that anaerobic iron reduction is mediated, at least in part, by an indirect mechanism. Evidence was obtained for an alternative model implicating the transfer of electrons from S-0 to Fe3+ via a respiratory chain that includes a bc(1) complex and a cytochrome c. Central carbon pathways were upregulated under aerobic conditions, correlating with higher growth rates, while many Calvin-Benson-Bassham cycle components were upregulated during anaerobic growth, probably as a result of more limited access to carbon dioxide. These results are important for understanding the role of A. ferrooxidans in environmental biogeochemical metal cycling and in industrial bioleaching operations.

Place, publisher, year, edition, pages
American Society for Microbiology, 2013
National Category
Microbiology
Identifiers
urn:nbn:se:umu:diva-60633 (URN)10.1128/AEM.03057-12 (DOI)000316183500008 ()
Note

Originally published in thesis in manuscript form

Available from: 2012-10-22 Created: 2012-10-22 Last updated: 2017-12-07Bibliographically approved
3. Extreme Zinc tolerance in Acidophilic microorganisms from the bacterial and Archaeal domains
Open this publication in new window or tab >>Extreme Zinc tolerance in Acidophilic microorganisms from the bacterial and Archaeal domains
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2013 (English)In: Extremophiles, ISSN 1431-0651, E-ISSN 1433-4909, Vol. 17, no 1, 75-85 p.Article in journal (Refereed) Published
Abstract [en]

Zinc can occur in extremely high concentrations in acidic, heavy metal polluted environments inhabited by acidophilic prokaryotes. Although these organisms are able to thrive in such severely contaminated ecosystems their resistance mechanisms have not been well studied. Bioinformatic analysis of a range of acidophilic bacterial and archaeal genomes identified homologues of several known zinc homeostasis systems. These included primary and secondary transporters, such as the primary heavy metal exporter ZntA and Nramp super-family secondary importer MntH. Three acidophilic model microorganisms, the archaeon 'Ferroplasma acidarmanus', the Gram negative bacterium Acidithiobacillus caldus, and the Gram positive bacterium Acidimicrobium ferrooxidans, were selected for detailed analyses. Zinc speciation modeling of the growth media demonstrated that a large fraction of the free metal ion is complexed, potentially affecting its toxicity. Indeed, many of the putative zinc homeostasis genes were constitutively expressed and with the exception of 'F. acidarmanus' ZntA, they were not up-regulated in the presence of excess zinc. Proteomic analysis revealed that zinc played a role in oxidative stress in At. caldus and Am. ferrooxidans. Furthermore, 'F. acidarmanus' kept a constant level of intracellular zinc over all conditions tested whereas the intracellular levels increased with increasing zinc exposure in the remaining organisms.

National Category
Microbiology
Identifiers
urn:nbn:se:umu:diva-60634 (URN)10.1007/s00792-012-0495-3 (DOI)
Available from: 2012-10-22 Created: 2012-10-22 Last updated: 2017-12-07Bibliographically approved
4. Response of Acidithiobacillus caldus towards suboptimal pH conditions
Open this publication in new window or tab >>Response of Acidithiobacillus caldus towards suboptimal pH conditions
(English)Manuscript (preprint) (Other academic)
National Category
Microbiology
Identifiers
urn:nbn:se:umu:diva-60635 (URN)
Available from: 2012-10-22 Created: 2012-10-22 Last updated: 2016-02-25

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