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They can be divided into aerobics and anaerobics. The former use [[hydrogen]] as an [[electron donor]] and oxygen as an acceptor while the latter use sulphate or nitrogen dioxide as [[Electron acceptor|electron acceptors]] <ref>{{Citation|last=Aragno|first=Michel|title=The Hydrogen-Oxidizing Bacteria|date=1981|url=https://doi.org/10.1007/978-3-662-13187-9_70|work=The Prokaryotes: A Handbook on Habitats, Isolation, and Identification of Bacteria|pages=865–893|editor-last=Starr|editor-first=Mortimer P.|publisher=Springer Berlin Heidelberg|language=en|doi=10.1007/978-3-662-13187-9_70|isbn=978-3-662-13187-9|access-date=2019-12-05|last2=Schlegel|first2=Hans G.|editor2-last=Stolp|editor2-first=Heinz|editor3-last=Trüper|editor3-first=Hans G.|editor4-last=Balows|editor4-first=Albert}}</ref>. Some species of both bacteria types have been isolated in different environments, for example in fresh waters, sediments, soils, activated sludge, hot springs, hydrothermal vents and percolating water <ref>{{Cite journal|last=Koskinen|first=Perttu E.P.|last2=Beck|first2=Steinar R.|last3=Örlygsson|first3=Jóhann|last4=Puhakka|first4=Jaakko A.|date=2008-04-23|title=Ethanol and hydrogen production by two thermophilic, anaerobic bacteria isolated from Icelandic geothermal areas|url=http://dx.doi.org/10.1002/bit.21942|journal=Biotechnology and Bioengineering|volume=101|issue=4|pages=679–690|doi=10.1002/bit.21942|issn=0006-3592}}</ref>.
They can be divided into aerobics and anaerobics. The former use [[hydrogen]] as an [[electron donor]] and oxygen as an acceptor while the latter use sulphate or nitrogen dioxide as [[Electron acceptor|electron acceptors]] <ref>{{Citation|last=Aragno|first=Michel|title=The Hydrogen-Oxidizing Bacteria|date=1981|url=https://doi.org/10.1007/978-3-662-13187-9_70|work=The Prokaryotes: A Handbook on Habitats, Isolation, and Identification of Bacteria|pages=865–893|editor-last=Starr|editor-first=Mortimer P.|publisher=Springer Berlin Heidelberg|language=en|doi=10.1007/978-3-662-13187-9_70|isbn=978-3-662-13187-9|access-date=2019-12-05|last2=Schlegel|first2=Hans G.|editor2-last=Stolp|editor2-first=Heinz|editor3-last=Trüper|editor3-first=Hans G.|editor4-last=Balows|editor4-first=Albert}}</ref>. Some species of both bacteria types have been isolated in different environments, for example in fresh waters, sediments, soils, activated sludge, hot springs, hydrothermal vents and percolating water <ref>{{Cite journal|last=Koskinen|first=Perttu E.P.|last2=Beck|first2=Steinar R.|last3=Örlygsson|first3=Jóhann|last4=Puhakka|first4=Jaakko A.|date=2008-04-23|title=Ethanol and hydrogen production by two thermophilic, anaerobic bacteria isolated from Icelandic geothermal areas|url=http://dx.doi.org/10.1002/bit.21942|journal=Biotechnology and Bioengineering|volume=101|issue=4|pages=679–690|doi=10.1002/bit.21942|issn=0006-3592}}</ref>.


These organisms are able to exploit the special properties of molecular hydrogen (for instance redox potential and diffusion coefficient) thanks to the presence of hydrogenases <ref>{{Cite journal|last=Barz|first=Martin|last2=Beimgraben|first2=Christian|last3=Staller|first3=Torsten|last4=Germer|first4=Frauke|last5=Opitz|first5=Friederike|last6=Marquardt|first6=Claudia|last7=Schwarz|first7=Christoph|last8=Gutekunst|first8=Kirstin|last9=Vanselow|first9=Klaus Heinrich|last10=Schmitz|first10=Ruth|last11=LaRoche|first11=Julie|date=2010-11-05|title=Distribution Analysis of Hydrogenases in Surface Waters of Marine and Freshwater Environments|url=http://dx.doi.org/10.1371/journal.pone.0013846|journal=PLoS ONE|volume=5|issue=11|pages=e13846|doi=10.1371/journal.pone.0013846|issn=1932-6203}}</ref>. The aerobic hydrogen oxidizing bacteria are facultative [[Autotroph|autotrophs]], but they can also have mixotrophic or completely [[Heterotroph|heterotrophic]] growth. Most of them show greater growth on organic substrates.The use of hydrogen as an electron donor coupled with the ability to synthesize organic mutter, through the reductive assimilation of CO<sub>2</sub>, characterize the hydrogen oxidizing bacteria. Among the most represented genres of these organisms we find: [[Caminibacter]], [[Aquifex]], [[Ralstonia]] and [[Paracoccus]].
These organisms are able to exploit the special properties of molecular hydrogen (for instance redox potential and diffusion coefficient) thanks to the presence of hydrogenases <ref>{{Cite journal|last=Barz|first=Martin|last2=Beimgraben|first2=Christian|last3=Staller|first3=Torsten|last4=Germer|first4=Frauke|last5=Opitz|first5=Friederike|last6=Marquardt|first6=Claudia|last7=Schwarz|first7=Christoph|last8=Gutekunst|first8=Kirstin|last9=Vanselow|first9=Klaus Heinrich|last10=Schmitz|first10=Ruth|last11=LaRoche|first11=Julie|date=2010-11-05|title=Distribution Analysis of Hydrogenases in Surface Waters of Marine and Freshwater Environments|url=http://dx.doi.org/10.1371/journal.pone.0013846|journal=PLoS ONE|volume=5|issue=11|pages=e13846|doi=10.1371/journal.pone.0013846|issn=1932-6203}}</ref>. The aerobic hydrogen oxidizing bacteria are facultative [[Autotroph|autotrophs]], but they can also have mixotrophic or completely [[Heterotroph|heterotrophic]] growth. Most of them show greater growth on organic substrates.The use of hydrogen as an electron donor coupled with the ability to synthesize organic mutter, through the reductive assimilation of CO<sub>2</sub>, characterize the hydrogen oxidizing bacteria. Among the most represented genres of these organisms we find: [[Caminibacter]], [[Aquifex]], [[Ralstonia]] and [[Paracoccus]].


== Hydrogen production and its distribution in the oceans ==
The most widespread compound on our [[Earth]] is [[hydrogen]], which represents around three-quarters of all the [[Chemical element|elements]].<ref name=":0">{{Cite journal|last=Das|first=Debabrata|last2=Veziroǧlu|first2=T. Nejat|date=2001-01-01|title=Hydrogen production by biological processes: a survey of literature|url=http://www.sciencedirect.com/science/article/pii/S0360319900000586|journal=International Journal of Hydrogen Energy|volume=26|issue=1|pages=13–28|doi=10.1016/S0360-3199(00)00058-6|issn=0360-3199}}</ref> In the [[atmosphere]], its concentration is about 0.5-0.6 ppm and so here it represents the most abundant [[trace gas]], after [[methane]].<ref name=":4">{{Cite journal|last=Barz|first=Martin|last2=Beimgraben|first2=Christian|last3=Staller|first3=Torsten|last4=Germer|first4=Frauke|last5=Opitz|first5=Friederike|last6=Marquardt|first6=Claudia|last7=Schwarz|first7=Christoph|last8=Gutekunst|first8=Kirstin|last9=Vanselow|first9=Klaus Heinrich|last10=Schmitz|first10=Ruth|last11=LaRoche|first11=Julie|date=2010-11-05|title=Distribution Analysis of Hydrogenases in Surface Waters of Marine and Freshwater Environments|url=http://dx.doi.org/10.1371/journal.pone.0013846|journal=PLoS ONE|volume=5|issue=11|pages=e13846|doi=10.1371/journal.pone.0013846|issn=1932-6203}}</ref> Therefore, H<sub>2</sub> can be used as [[energy]] source in several biological processes, also because it has a highly negative [[redox potential]] (E<sub>0</sub>’= -0.414 V) . It can be coupled with different compounds:

-       O<sub>2</sub>: the oxic respiration is performed (H<sub>2</sub>+1/2O<sub>2</sub> → H<sub>2</sub>O)

-       Oxidized compounds, such as [[carbon dioxide]] or [[sulfate]]. <ref>{{Cite journal|last=Heimann|first=Axel|last2=Jakobsen|first2=Rasmus|last3=Blodau|first3=Christian|date=January 2010|title=Energetic Constraints on H 2 -Dependent Terminal Electron Accepting Processes in Anoxic Environments: A Review of Observations and Model Approaches|url=https://pubs.acs.org/doi/10.1021/es9018207|journal=Environmental Science & Technology|language=en|volume=44|issue=1|pages=24–33|doi=10.1021/es9018207|issn=0013-936X|via=}}</ref>

In the ecosystems, hydrogen can be produced through biological and abiotic processes .

The abiotic processes are mainly due to geothermal production <ref name=":1">{{Citation|last=Aragno|first=Michel|title=Thermophilic, Aerobic, Hydrogen-Oxidizing (Knallgas) Bacteria|date=1992|url=https://doi.org/10.1007/978-1-4757-2191-1_55|work=The Prokaryotes: A Handbook on the Biology of Bacteria: Ecophysiology, Isolation, Identification, Applications|pages=3917–3933|editor-last=Balows|editor-first=Albert|publisher=Springer New York|language=en|doi=10.1007/978-1-4757-2191-1_55|isbn=978-1-4757-2191-1|access-date=2019-12-03|editor2-last=Trüper|editor2-first=Hans G.|editor3-last=Dworkin|editor3-first=Martin|editor4-last=Harder|editor4-first=Wim}}</ref> and [[serpentinization]] <ref name=":2">{{Cite journal|last=Brazelton|first=William J.|last2=Nelson|first2=Bridget|last3=Schrenk|first3=Matthew O.|date=2012|title=Metagenomic Evidence for H2 Oxidation and H2 Production by Serpentinite-Hosted Subsurface Microbial Communities|url=http://journal.frontiersin.org/article/10.3389/fmicb.2011.00268/abstract|journal=Frontiers in Microbiology|volume=2|doi=10.3389/fmicb.2011.00268|issn=1664-302X|pmc=PMC3252642|pmid=22232619}}</ref>. In the first case, hydrogen is usually present as a [[gas]] and probably can be obtained by different reactions:

1.      Water may react with [[silicon]] radical at high temperature:

Si· + H<sub>2</sub>O → SiOH + H·

H· + H· → H<sub>2</sub>

2.      The proposed reaction between [[iron]] oxides and [[water]], at [[Temperature|temperatures]] higher than 800°C:

2FeO + H<sub>2</sub>O → Fe<sub>2</sub>O<sub>3</sub> + H<sub>2</sub>

2Fe<sub>3</sub>O<sub>4</sub> + H<sub>2</sub>O → 3Fe<sub>2</sub>O<sub>3</sub> + H<sub>2</sub> <ref name=":1" />

On the other hand, serpentinization is an exothermic geochemical mechanism that occurs when, thanks to the [[Tectonics|tectonic]] movements, the ultramafic rocks raise and reach the water. This process can bring to the production of large quantities of H<sub>2</sub>, but also of [[methane]] and organic substances. <ref name=":2" />

The main mechanisms that lead to the formation of hydrogen, involving different microorganisms, are [[nitrogen fixation]] and [[fermentation]]. The first one happens in some bacteria, such as heterocystous and non-heterocystous [[cyanobacteria]], that have a specialized enzyme, the [[nitrogenase]], which catalizes the reduction of N<sub>2</sub> to NH<sub>4</sub><sup>+</sup>. In addition, these microorganisms have another enzyme, the [[hydrogenase]], that oxidizes the H<sub>2</sub> realeased as a by-product. <ref name=":0" /> Therefore, in this type of bacteria, the amount of hydrogen produced depends on the ratio between H<sub>2</sub> production and consumption.<ref name=":3">{{Cite journal|last=Tiwari|first=Archana|last2=Pandey|first2=Anjana|date=January 2012|title=Cyanobacterial hydrogen production – A step towards clean environment|url=http://dx.doi.org/10.1016/j.ijhydene.2011.09.100|journal=International Journal of Hydrogen Energy|volume=37|issue=1|pages=139–150|doi=10.1016/j.ijhydene.2011.09.100|issn=0360-3199|via=}}</ref> In some cases, the H<sub>2</sub> can be present in the environments because the N<sub>2</sub>-fixing bacteria can have a low quantity of hydrogenases. <ref>{{Cite journal|last=Pumphrey|first=Graham M.|last2=Ranchou-Peyruse|first2=Anthony|last3=Spain|first3=Jim C.|date=2011-05-27|title=Cultivation-Independent Detection of Autotrophic Hydrogen-Oxidizing Bacteria by DNA Stable-Isotope Probing|url=http://dx.doi.org/10.1128/aem.00285-11|journal=Applied and Environmental Microbiology|volume=77|issue=14|pages=4931–4938|doi=10.1128/aem.00285-11|issn=0099-2240}}</ref><ref name=":3" /> Instead, [[fermentation]] is performed by some strict or facultative anaerobic [[Heterotroph|heterotrophic]] bacteria, in particular [[Clostridia]] <ref>{{Cite journal|last=Adams|first=Michael W. W.|last2=Stiefel|first2=Edward I.|date=1998-12-04|title=Biological Hydrogen Production: Not So Elementary|url=https://science.sciencemag.org/content/282/5395/1842|journal=Science|language=en|volume=282|issue=5395|pages=1842–1843|doi=10.1126/science.282.5395.1842|issn=0036-8075|pmid=9874636}}</ref> ,that degrade organic molecules, producing hydrogen as one of the products. Therefore, this type of [[metabolism]] mainly occurs in anoxic sites, such as lake [[Sediment|sediments]], deep-sea [[Hydrothermal vent|hydrothermal vents]] and human gut. <ref>{{Cite journal|last=Adam|first=Nicole|last2=Perner|first2=Mirjam|date=2018|title=Microbially Mediated Hydrogen Cycling in Deep-Sea Hydrothermal Vents|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6265342/|journal=Frontiers in Microbiology|language=en|volume=9|doi=10.3389/fmicb.2018.02873|pmid=30532749}}</ref>

Probably mainly due to the biotic processes, in the marine habitats it was observed that the concentrations of hydrogen were supersaturated. In all these environments, the highest concentrations were in the first metres, decreasing to the [[thermocline]] and reaching the lowest concentrations in the deep [[Ocean|oceans]]. <ref name=":4" /> Globally, [[Tropics|tropical]] and [[Subtropics|subtropical]] oceans appear to have the most abundant quantity of H<sub>2</sub> <ref name=":5">{{Cite journal|last=Herr|first=Frank L.|last2=Frank|first2=Ernest C.|last3=Leone|first3=Gerald M.|last4=Kennicutt|first4=Mahlon C.|date=January 1984|title=Diurnal variability of dissolved molecular hydrogen in the tropical South Atlantic Ocean|url=http://dx.doi.org/10.1016/0198-0149(84)90069-4|journal=Deep Sea Research Part A. Oceanographic Research Papers|volume=31|issue=1|pages=13–20|doi=10.1016/0198-0149(84)90069-4|issn=0198-0149|via=}}</ref><ref name=":4" /><ref name=":6">{{Cite journal|last=Conrad|first=Ralf|last2=Seiler|first2=Wolfgang|date=December 1988|title=Methane and hydrogen in seawater (Atlantic Ocean)|url=http://dx.doi.org/10.1016/0198-0149(88)90116-1|journal=Deep Sea Research Part A. Oceanographic Research Papers|volume=35|issue=12|pages=1903–1917|doi=10.1016/0198-0149(88)90116-1|issn=0198-0149|via=}}</ref>, while the least amount is present in higher [[Latitude|latitudes]] <ref name=":4" /><ref>{{Cite journal|last=Herr|first=Frank L.|last2=Scranton|first2=Mary I.|last3=Barger|first3=William R.|date=September 1981|title=Dissolved hydrogen in the Norwegian Sea: Mesoscale surface variability and deep-water distribution|url=http://dx.doi.org/10.1016/0198-0149(81)90014-5|journal=Deep Sea Research Part A. Oceanographic Research Papers|volume=28|issue=9|pages=1001–1016|doi=10.1016/0198-0149(81)90014-5|issn=0198-0149|via=}}</ref><ref>{{Cite journal|last=Punshon|first=Stephen|last2=Moore|first2=Robert M.|last3=Xie|first3=Huixiang|date=April 2007|title=Net loss rates and distribution of molecular hydrogen (H2) in mid-latitude coastal waters|url=http://dx.doi.org/10.1016/j.marchem.2007.01.009|journal=Marine Chemistry|volume=105|issue=1-2|pages=129–139|doi=10.1016/j.marchem.2007.01.009|issn=0304-4203|via=}}</ref>. However, it was observed that the realease of hydrogen in the oceans is dependent on the solar [[radiation]], showing a daily change with the maximum peak at noon <ref name=":4" /><ref name=":5" /><ref name=":6" />. Nitrogen fixation, performed by cyanobacteria, leads to the production of one molecule of H<sub>2</sub> at least. This metabolism is thought to be the major one involved in the increase of H<sub>2</sub> in the oceans <ref name=":4" />. Despite there are some evidences of this <ref>{{Cite journal|last=Lindberg|first=P.|last2=Lindblad|first2=P.|last3=Cournac|first3=L.|date=2004-04-01|title=Gas Exchange in the Filamentous Cyanobacterium Nostoc punctiforme Strain ATCC 29133 and Its Hydrogenase-Deficient Mutant Strain NHM5|url=http://dx.doi.org/10.1128/aem.70.4.2137-2145.2004|journal=Applied and Environmental Microbiology|volume=70|issue=4|pages=2137–2145|doi=10.1128/aem.70.4.2137-2145.2004|issn=0099-2240}}</ref><ref>{{Cite journal|last=Wilson|first=ST|last2=Foster|first2=RA|last3=Zehr|first3=JP|last4=Karl|first4=DM|date=2010-04-08|title=Hydrogen production by Trichodesmium erythraeum Cyanothece sp. and Crocosphaera watsonii|url=http://dx.doi.org/10.3354/ame01407|journal=Aquatic Microbial Ecology|volume=59|pages=197–206|doi=10.3354/ame01407|issn=0948-3055}}</ref>, more data need to be collected to finally correlate the two phenomena.

=='''References'''==
<references />

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Revision as of 09:57, 23 December 2019

Hydrogen oxidizing bacteria are a group of facultative autotrophs that can use hydrogen as electron donor.

They can be divided into aerobics and anaerobics. The former use hydrogen as an electron donor and oxygen as an acceptor while the latter use sulphate or nitrogen dioxide as electron acceptors [1]. Some species of both bacteria types have been isolated in different environments, for example in fresh waters, sediments, soils, activated sludge, hot springs, hydrothermal vents and percolating water [2].

These organisms are able to exploit the special properties of molecular hydrogen (for instance redox potential and diffusion coefficient) thanks to the presence of hydrogenases [3]. The aerobic hydrogen oxidizing bacteria are facultative autotrophs, but they can also have mixotrophic or completely heterotrophic growth. Most of them show greater growth on organic substrates.The use of hydrogen as an electron donor coupled with the ability to synthesize organic mutter, through the reductive assimilation of CO2, characterize the hydrogen oxidizing bacteria. Among the most represented genres of these organisms we find: Caminibacter, Aquifex, Ralstonia and Paracoccus.

Hydrogen production and its distribution in the oceans

The most widespread compound on our Earth is hydrogen, which represents around three-quarters of all the elements.[4] In the atmosphere, its concentration is about 0.5-0.6 ppm and so here it represents the most abundant trace gas, after methane.[5] Therefore, H2 can be used as energy source in several biological processes, also because it has a highly negative redox potential (E0’= -0.414 V) . It can be coupled with different compounds:

-       O2: the oxic respiration is performed (H2+1/2O2 → H2O)

-       Oxidized compounds, such as carbon dioxide or sulfate. [6]

In the ecosystems, hydrogen can be produced through biological and abiotic processes .

The abiotic processes are mainly due to geothermal production [7] and serpentinization [8]. In the first case, hydrogen is usually present as a gas and probably can be obtained by different reactions:

1.      Water may react with silicon radical at high temperature:

Si· + H2O → SiOH + H·

H· + H· → H2

2.      The proposed reaction between iron oxides and water, at temperatures higher than 800°C:

2FeO + H2O → Fe2O3 + H2

2Fe3O4 + H2O → 3Fe2O3 + H2 [7]

On the other hand, serpentinization is an exothermic geochemical mechanism that occurs when, thanks to the tectonic movements, the ultramafic rocks raise and reach the water. This process can bring to the production of large quantities of H2, but also of methane and organic substances. [8]

The main mechanisms that lead to the formation of hydrogen, involving different microorganisms, are nitrogen fixation and fermentation. The first one happens in some bacteria, such as heterocystous and non-heterocystous cyanobacteria, that have a specialized enzyme, the nitrogenase, which catalizes the reduction of N2 to NH4+. In addition, these microorganisms have another enzyme, the hydrogenase, that oxidizes the H2 realeased as a by-product. [4] Therefore, in this type of bacteria, the amount of hydrogen produced depends on the ratio between H2 production and consumption.[9] In some cases, the H2 can be present in the environments because the N2-fixing bacteria can have a low quantity of hydrogenases. [10][9] Instead, fermentation is performed by some strict or facultative anaerobic heterotrophic bacteria, in particular Clostridia [11] ,that degrade organic molecules, producing hydrogen as one of the products. Therefore, this type of metabolism mainly occurs in anoxic sites, such as lake sediments, deep-sea hydrothermal vents and human gut. [12]

Probably mainly due to the biotic processes, in the marine habitats it was observed that the concentrations of hydrogen were supersaturated. In all these environments, the highest concentrations were in the first metres, decreasing to the thermocline and reaching the lowest concentrations in the deep oceans. [5] Globally, tropical and subtropical oceans appear to have the most abundant quantity of H2 [13][5][14], while the least amount is present in higher latitudes [5][15][16]. However, it was observed that the realease of hydrogen in the oceans is dependent on the solar radiation, showing a daily change with the maximum peak at noon [5][13][14]. Nitrogen fixation, performed by cyanobacteria, leads to the production of one molecule of H2 at least. This metabolism is thought to be the major one involved in the increase of H2 in the oceans [5]. Despite there are some evidences of this [17][18], more data need to be collected to finally correlate the two phenomena.

References

  1. ^ Aragno, Michel; Schlegel, Hans G. (1981), Starr, Mortimer P.; Stolp, Heinz; Trüper, Hans G.; Balows, Albert (eds.), "The Hydrogen-Oxidizing Bacteria", The Prokaryotes: A Handbook on Habitats, Isolation, and Identification of Bacteria, Springer Berlin Heidelberg, pp. 865–893, doi:10.1007/978-3-662-13187-9_70, ISBN 978-3-662-13187-9, retrieved 2019-12-05
  2. ^ Koskinen, Perttu E.P.; Beck, Steinar R.; Örlygsson, Jóhann; Puhakka, Jaakko A. (2008-04-23). "Ethanol and hydrogen production by two thermophilic, anaerobic bacteria isolated from Icelandic geothermal areas". Biotechnology and Bioengineering. 101 (4): 679–690. doi:10.1002/bit.21942. ISSN 0006-3592.
  3. ^ Barz, Martin; Beimgraben, Christian; Staller, Torsten; Germer, Frauke; Opitz, Friederike; Marquardt, Claudia; Schwarz, Christoph; Gutekunst, Kirstin; Vanselow, Klaus Heinrich; Schmitz, Ruth; LaRoche, Julie (2010-11-05). "Distribution Analysis of Hydrogenases in Surface Waters of Marine and Freshwater Environments". PLoS ONE. 5 (11): e13846. doi:10.1371/journal.pone.0013846. ISSN 1932-6203.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  4. ^ a b Das, Debabrata; Veziroǧlu, T. Nejat (2001-01-01). "Hydrogen production by biological processes: a survey of literature". International Journal of Hydrogen Energy. 26 (1): 13–28. doi:10.1016/S0360-3199(00)00058-6. ISSN 0360-3199.
  5. ^ a b c d e f Barz, Martin; Beimgraben, Christian; Staller, Torsten; Germer, Frauke; Opitz, Friederike; Marquardt, Claudia; Schwarz, Christoph; Gutekunst, Kirstin; Vanselow, Klaus Heinrich; Schmitz, Ruth; LaRoche, Julie (2010-11-05). "Distribution Analysis of Hydrogenases in Surface Waters of Marine and Freshwater Environments". PLoS ONE. 5 (11): e13846. doi:10.1371/journal.pone.0013846. ISSN 1932-6203.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  6. ^ Heimann, Axel; Jakobsen, Rasmus; Blodau, Christian (January 2010). "Energetic Constraints on H 2 -Dependent Terminal Electron Accepting Processes in Anoxic Environments: A Review of Observations and Model Approaches". Environmental Science & Technology. 44 (1): 24–33. doi:10.1021/es9018207. ISSN 0013-936X.
  7. ^ a b Aragno, Michel (1992), Balows, Albert; Trüper, Hans G.; Dworkin, Martin; Harder, Wim (eds.), "Thermophilic, Aerobic, Hydrogen-Oxidizing (Knallgas) Bacteria", The Prokaryotes: A Handbook on the Biology of Bacteria: Ecophysiology, Isolation, Identification, Applications, Springer New York, pp. 3917–3933, doi:10.1007/978-1-4757-2191-1_55, ISBN 978-1-4757-2191-1, retrieved 2019-12-03
  8. ^ a b Brazelton, William J.; Nelson, Bridget; Schrenk, Matthew O. (2012). "Metagenomic Evidence for H2 Oxidation and H2 Production by Serpentinite-Hosted Subsurface Microbial Communities". Frontiers in Microbiology. 2. doi:10.3389/fmicb.2011.00268. ISSN 1664-302X. PMC 3252642. PMID 22232619.{{cite journal}}: CS1 maint: PMC format (link) CS1 maint: unflagged free DOI (link)
  9. ^ a b Tiwari, Archana; Pandey, Anjana (January 2012). "Cyanobacterial hydrogen production – A step towards clean environment". International Journal of Hydrogen Energy. 37 (1): 139–150. doi:10.1016/j.ijhydene.2011.09.100. ISSN 0360-3199.
  10. ^ Pumphrey, Graham M.; Ranchou-Peyruse, Anthony; Spain, Jim C. (2011-05-27). "Cultivation-Independent Detection of Autotrophic Hydrogen-Oxidizing Bacteria by DNA Stable-Isotope Probing". Applied and Environmental Microbiology. 77 (14): 4931–4938. doi:10.1128/aem.00285-11. ISSN 0099-2240.
  11. ^ Adams, Michael W. W.; Stiefel, Edward I. (1998-12-04). "Biological Hydrogen Production: Not So Elementary". Science. 282 (5395): 1842–1843. doi:10.1126/science.282.5395.1842. ISSN 0036-8075. PMID 9874636.
  12. ^ Adam, Nicole; Perner, Mirjam (2018). "Microbially Mediated Hydrogen Cycling in Deep-Sea Hydrothermal Vents". Frontiers in Microbiology. 9. doi:10.3389/fmicb.2018.02873. PMID 30532749.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  13. ^ a b Herr, Frank L.; Frank, Ernest C.; Leone, Gerald M.; Kennicutt, Mahlon C. (January 1984). "Diurnal variability of dissolved molecular hydrogen in the tropical South Atlantic Ocean". Deep Sea Research Part A. Oceanographic Research Papers. 31 (1): 13–20. doi:10.1016/0198-0149(84)90069-4. ISSN 0198-0149.
  14. ^ a b Conrad, Ralf; Seiler, Wolfgang (December 1988). "Methane and hydrogen in seawater (Atlantic Ocean)". Deep Sea Research Part A. Oceanographic Research Papers. 35 (12): 1903–1917. doi:10.1016/0198-0149(88)90116-1. ISSN 0198-0149.
  15. ^ Herr, Frank L.; Scranton, Mary I.; Barger, William R. (September 1981). "Dissolved hydrogen in the Norwegian Sea: Mesoscale surface variability and deep-water distribution". Deep Sea Research Part A. Oceanographic Research Papers. 28 (9): 1001–1016. doi:10.1016/0198-0149(81)90014-5. ISSN 0198-0149.
  16. ^ Punshon, Stephen; Moore, Robert M.; Xie, Huixiang (April 2007). "Net loss rates and distribution of molecular hydrogen (H2) in mid-latitude coastal waters". Marine Chemistry. 105 (1–2): 129–139. doi:10.1016/j.marchem.2007.01.009. ISSN 0304-4203.
  17. ^ Lindberg, P.; Lindblad, P.; Cournac, L. (2004-04-01). "Gas Exchange in the Filamentous Cyanobacterium Nostoc punctiforme Strain ATCC 29133 and Its Hydrogenase-Deficient Mutant Strain NHM5". Applied and Environmental Microbiology. 70 (4): 2137–2145. doi:10.1128/aem.70.4.2137-2145.2004. ISSN 0099-2240.
  18. ^ Wilson, ST; Foster, RA; Zehr, JP; Karl, DM (2010-04-08). "Hydrogen production by Trichodesmium erythraeum Cyanothece sp. and Crocosphaera watsonii". Aquatic Microbial Ecology. 59: 197–206. doi:10.3354/ame01407. ISSN 0948-3055.



Hydrogen oxidizing bacteria, or sometimes Knallgas-bacteria, are bacteria that oxidize hydrogen as a source of energy with oxygen as final electron acceptor. See microbial metabolism (hydrogen oxidation). These bacteria include Hydrogenobacter thermophilus, Cupriavidus necator, Hydrogenovibrio marinus, and Helicobacter pylori.[1] There are both Gram positive and Gram negative knallgas bacteria.

Most grow best under microaerobic conditions. They do this because the hydrogenase enzyme used in hydrogen oxidation is inhibited by the presence of oxygen, but oxygen is still needed as a terminal electron acceptor.[2]

The word Knallgas means "oxyhydrogen" (a mixture of hydrogen and oxygen, literally "bang-gas") in Germanic languages.


Knallgas bacteria : metabolism

The aerobic hydrogen oxidizing bacteria, more known as Knallgas bacteria, are a group of bacteria which are able to fix carbon dioxide using H2 as electron donor and energy source and O2 as terminal electron acceptor. Actually, Knallgas bacteria stand out from the hydrogen oxydizing bacteria which, although using H2 as an electron donor, are not able to fix CO2, as Knallgas do. [3]

This aerobic hydrogen oxidation, also known as the Knallgas reaction, which releases a considerable amount of energy, determines the formation of proton motive force (PMF).

H2 + O2 H2O ΔG0 = -237 Kj

The key enzymes involved in this reaction are the hydrogenase which lead the electrons through the electron transport chain, from hydrogen to the final acceptor, that is O2 which is actually reduced in water, the only by-product.[4] The hydrogenases that are divided into three categories according to the type of metal present in the active site, are the enzymes that allow the oxidation of hydrogen. The first evidence of the presence of these enzymes has been found for the first time in Pseudomonas saccharophila, Alcaligenes ruhlandii and Alcaligenese eutrophus in which there were two types of hydrogenases: cytoplasmatic and membrane-bound. If the first enzyme takes up hydrogen and reduce the NAD+ in NADH for carbon fixation, the second is involved in the generation of the proton motive force. [5][6] Anyway, in most of the knallgas bacteria only one type of hydrogensase was observed, the one bound to the membrane that provided hydrogen activation.[7]

These microorganisms are also defined as facultative authotrophs, neverthless some of them are also able to live in completly heterotrophic conditions using organic substances as electron donor and energy source, even if in this case the hydrogenase activity takes on less importance or is completely absent. [8]

However, Knallgas bacteria, growing as chemolithoautotrophs, as soon as they integrate every molecule of Co2, they can produce, through the Calvin Benson Cycle or reverse citric acid cycle (TCA cycle), biomolecules necessary for the cell.[9][10]

6H2 + 2O2 + CO2 (CH2O) + 5H2O

In particular, a recent study carried out on Alcaligenes eutropha, one of the most representative species of Knallgas bacteria,  highlighted that at low concentrations of O2 (about 10 mol %) and consequently with a low ΔH2/ΔCO2 molar ratio (3.3), the energy efficiency of Co2 fixation increasing until of 50%.This is an interesting characteristic of these microorganisms because once assimilated, the carbon dioxide is reduced to polyhydroxybutyrate , from which its derivatives, being biodegradable, are used in various eco-sustainable applications.[11][12]

References

  1. ^ Olson JW and Maier RJ (2002) Molecular hydrogen as an energy source for Helicobacter pylori. Science 298:1788-90. full text
  2. ^ Jugder, Bat-Erdene; Welch, Jeffrey; Aguey-Zinsou, Kondo-Francois; Marquis, Christopher P. (2013). "Fundamentals and electrochemical applications of [Ni–Fe]-uptake hydrogenases". RSC Advances. 3 (22): 8142. doi:10.1039/c3ra22668a. ISSN 2046-2069.
  3. ^ "Physiological and phylogenetic studies of thermophilic, hydrogen and sulfur oxidizing bacteria isolated from Icelandic geothermal areas" (PDF). 2008. {{cite web}}: |first= missing |last= (help)CS1 maint: url-status (link)
  4. ^ Bowien, B; Schlegel, H G (1981-10-01). "Physiology and Biochemistry of Aerobic Hydrogen-Oxidizing Bacteria". Annual Review of Microbiology. 35 (1): 405–452. doi:10.1146/annurev.mi.35.100181.002201. ISSN 0066-4227.
  5. ^ Schink, Bernhard; Schlegel, Hans-Günter (1978-06-13). "Hydrogen metabolism in aerobic hydrogen-oxidizing bacteria". Biochimie. 60 (3): 297–305. doi:10.1016/S0300-9084(78)80826-8. ISSN 0300-9084.
  6. ^ Appel, Jens; Schulz, Rüdiger (1998-11-01). "Hydrogen metabolism in organisms with oxygenic photosynthesis: hydrogenases as important regulatory devices for a proper redox poising?". Journal of Photochemistry and Photobiology B: Biology. 47 (1): 1–11. doi:10.1016/S1011-1344(98)00179-1. ISSN 1011-1344.
  7. ^ Schneider, Klaus; Schlegel, Hans G. (1977). "Localization and stability of hydrogenases from aerobic hydrogen bacteria". Archives of Microbiology. 112 (3): 229–238. doi:10.1007/BF00413086. ISSN 0302-8933.
  8. ^ Aragno, Michel; Schlegel, Hans G. (1981), Starr, Mortimer P.; Stolp, Heinz; Trüper, Hans G.; Balows, Albert (eds.), "The Hydrogen-Oxidizing Bacteria", The Prokaryotes: A Handbook on Habitats, Isolation, and Identification of Bacteria, Springer Berlin Heidelberg, pp. 865–893, doi:10.1007/978-3-662-13187-9_70, ISBN 978-3-662-13187-9, retrieved 2019-12-03
  9. ^ Schlegel, H. G.; Eberhardt, U. (1972-01-01), Rose, A. H.; Tempest, D. W. (eds.), "Regulatory Phenomena in the Metabolism of Knallgasbacteria", Advances in Microbial Physiology, vol. 7, Academic Press, pp. 205–242, doi:10.1016/s0065-2911(08)60079-x, retrieved 2019-12-03
  10. ^ Madigan, Michael T.; Martinko, John M; Parker, Jack; Brock, Thomas D. (2003). Brock, biology of microorganisms (10th ed / Michael T. Madigan, John M. Martinko, Jack Parker ed.). Upper Saddle River, N.J Prentice Hall. ISBN 978-0-13-049147-3.{{cite book}}: CS1 maint: date and year (link)
  11. ^ Yu, Jian; Dow, Allexa; Pingali, Sricanth (2013-07-17). "The energy efficiency of carbon dioxide fixation by a hydrogen-oxidizing bacterium". International Journal of Hydrogen Energy. 38 (21): 8683–8690. doi:10.1016/j.ijhydene.2013.04.153. ISSN 0360-3199. {{cite journal}}: no-break space character in |title= at position 52 (help)
  12. ^ Ishizaki, Ayaaki; Tanaka, Kenji (1990-01-01). "Batch culture of Alcaligenes eutrophus ATCC 17697T using recycled gas closed circuit culture system". Journal of Fermentation and Bioengineering. 69 (3): 170–174. doi:10.1016/0922-338X(90)90041-T. ISSN 0922-338X.


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