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Oxygen-dependent regulation of key components in microbial chlorate respiration
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Contamination of perchlorate and chlorate in nature is primarily the result of various industrial processes. The microbial respiration of these oxyanions of chlorine plays a major role in reducing the society’s impact on the environment. The focus with this thesis is to investigate the oxygen-dependent regulation of key components involved in the chlorate respiration in the gram‑negative bacterium Ideonella dechloratans. Chlorate metabolism is based on the action of the enzymes chlorate reductase and chlorite dismutase and results in the end products molecular oxygen and chloride ion. Up‑regulation of chlorite dismutase activity in the absence of oxygen is demonstrated to occur at the transcriptional level, with the participation of the transcriptional fumarate and nitrate reduction regulator (FNR). Also, the chlorate reductase enzyme was shown to be regulated at the transcriptional level with the possible involvement of additional regulating mechanisms as well. Interestingly, the corresponding chlorate reductase operon was found to be part of a polycistronic mRNA which also comprises the gene for a cytochrome c and a putative transcriptional regulator protein.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2016.
Series
Karlstad University Studies, ISSN 1403-8099 ; 13
Keyword [en]
Anaerobic respiration, Gene expression, Chlorate, Chlorate reductase, Chlorite dismutase
National Category
Chemical Engineering
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:kau:diva-40698ISBN: 978-91-7063-692-9 (print)OAI: oai:DiVA.org:kau-40698DiVA: diva2:906974
Public defence
2016-04-08, Rejmersalen, 9C204, Karlstad, 09:00 (Swedish)
Opponent
Supervisors
Available from: 2016-03-18 Created: 2016-02-25 Last updated: 2016-04-20Bibliographically approved
List of papers
1. Expression of Chlorite Dismutase and Chlorate Reductase in the Prescence of Oxygen and/or Chlorate as the Terminal Electron Acceptor in Ideonella dechloratans
Open this publication in new window or tab >>Expression of Chlorite Dismutase and Chlorate Reductase in the Prescence of Oxygen and/or Chlorate as the Terminal Electron Acceptor in Ideonella dechloratans
2012 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 78, no 12, 4380-4385 p.Article in journal (Refereed) Published
Abstract [en]

The ability of microorganisms to perform dissimilatory (per)chlorate reduction is, for most species, known to be oxygen sensitive. Consequently, bioremediation processes for the removal of oxochlorates will be disturbed if oxygen is present. We measured the expression of chlorite dismutase and chlorate reductase in the presence of different terminal electron acceptors in the chlorate reducer Ideonella dechloratans. Enzyme activity assays and mRNA analyses by real-time quantitative reverse transcription (qRT)-PCR were performed on cell extracts from cells grown aerobically with and without chlorate and on cells grown anaerobically in the presence of chlorate. Our results showed that both chlorite dismutase and chlorate reductase are expressed during aerobic growth. However, transfer to anaerobic conditions with chlorate resulted in significantly enhanced enzyme activities and mRNA levels for both enzymes. Absence of oxygen was necessary for the induction to occur, since chlorate addition under aerobic conditions produced neither increased enzyme activities nor higher relative levels of mRNA. For chlorite dismutase, the observed increase in activity was on the same order of magnitude as the increase in the relative mRNA level, indicating gene regulation at the transcriptional level. However, chlorate reductase showed about 200 times higher enzyme activity in anaerobically induced cells, whereas the increase in mRNA was only about 10-fold, suggesting additional mechanisms influence the enzyme activity.

National Category
Natural Sciences
Identifiers
urn:nbn:se:kau:diva-13406 (URN)10.1128/AEM.07303-11 (DOI)000304788500042 ()
Available from: 2012-05-29 Created: 2012-05-29 Last updated: 2017-12-07Bibliographically approved
2. Chlorate reductase is cotranscribed with cytochrome c and other downstream genes in the gene cluster for chlorate respiration of Ideonella dechloratans
Open this publication in new window or tab >>Chlorate reductase is cotranscribed with cytochrome c and other downstream genes in the gene cluster for chlorate respiration of Ideonella dechloratans
2015 (English)In: FEMS Microbiology Letters, ISSN 0378-1097, E-ISSN 1574-6968, Vol. 362, no 6Article in journal (Refereed) Published
Abstract [en]

The chlorate-respiring bacterium Ideonella dechloratans is a facultative anaerobe that can use both oxygen and chlorate as terminal electron acceptors. The genes for the enzymes chlorate reductase (clrABDC) and chlorite dismutase, necessary for chlorate metabolism and probably acquired by lateral gene transfer, are located in a gene cluster that also includes other genes potentially important for chlorate metabolism. Among those are a gene for cytochrome c (cyc) whose gene product may serve as an electron carrier during chlorate reduction, a cofactor biosynthesis gene (mobB) and a predicted transcriptional regulator (arsR). Only chlorate reductase and chlorite dismutase have been shown to be expressed in vivo. Here, we report the in vivo production of a single polycistronic transcript covering eight open reading frames including clrABDC, cyc, mobB and arsR. Transcription levels of the cyc and clrA genes were compared to each other by the use of qRT-PCR in RNA preparations from cells grown under aerobic or chlorate reducing anaerobic conditions. The two genes showed the same mRNA levels under both growth regimes, indicating that no transcription termination occurs between them. Higher transcription levels were observed at growth without external oxygen supply. Implications for electron pathway integration following lateral gene transfer are discussed.

Keyword
anaerobic respiration; gene expression; oxochlorates
National Category
Biological Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:kau:diva-40700 (URN)10.1093/femsle/fnv019 (DOI)000356885900007 ()
Available from: 2016-02-25 Created: 2016-02-25 Last updated: 2017-12-06Bibliographically approved
3. Anoxic induction of the chlorite dismutase gene of Ideonella dechloratans is dependent of the fumarate and nitrate reduction regulator
Open this publication in new window or tab >>Anoxic induction of the chlorite dismutase gene of Ideonella dechloratans is dependent of the fumarate and nitrate reduction regulator
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Chemical Engineering
Research subject
Chemistry
Identifiers
urn:nbn:se:kau:diva-40714 (URN)
Available from: 2016-02-25 Created: 2016-02-25 Last updated: 2017-02-15
4. An Fnr-type transcriptional regulator is responsible for anoxic up-regulation of chlorite dismutase in Ideonella dechloratans
Open this publication in new window or tab >>An Fnr-type transcriptional regulator is responsible for anoxic up-regulation of chlorite dismutase in Ideonella dechloratans
(English)Manuscript (preprint) (Other academic)
Abstract
National Category
Chemical Engineering
Research subject
Chemistry
Identifiers
urn:nbn:se:kau:diva-40715 (URN)
Available from: 2016-02-25 Created: 2016-02-25 Last updated: 2016-07-11

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