Okenane

Last updated
Okenane
Okenane.svg
Names
IUPAC name
1-(3,7,12,16,20,24-Hexamethylpentacosyl)-2,3,4-trimethylbenzene
Other names
chi,psi-Carotane
Identifiers
3D model (JSmol)
PubChem CID
  • InChI=1S/C40H74/c1-31(2)17-13-20-34(5)23-15-25-35(6)24-14-21-32(3)18-11-12-19-33(4)22-16-26-36(7)27-29-40-30-28-37(8)38(9)39(40)10/h28,30-36H,11-27,29H2,1-10H3
    Key: SRAMWFMBIKLRNA-UHFFFAOYSA-N
  • C=1C=C(C(=C(C1C)C)C)CCC(C)CCCC(C)CCCCC(C)CCCC(C)CCCC(C)CCCC(C)C
Properties
C40H74
Molar mass 555.032 g·mol−1
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Okenane, the diagenetic end product of okenone, is a biomarker for Chromatiaceae, the purple sulfur bacteria. [1] These anoxygenic phototrophs use light for energy and sulfide as their electron donor and sulfur source. Discovery of okenane in marine sediments implies a past euxinic environment, where water columns were anoxic and sulfidic. This is potentially tremendously important for reconstructing past oceanic conditions, but so far okenane has only been identified in one Paleoproterozoic (1.6 billion years old) rock sample from Northern Australia. [2] [3]

Contents

Background

Purple sulfur bacteria produce the pigment molecule okenone, which is then diagenetically altered and preserved as the partially saturated okenane. Discovering okenane in sediments is considered evidence of purple sulfur bacteria, implying an anoxic and sulfidic environment. Okenone and Okenane.png
Purple sulfur bacteria produce the pigment molecule okenone, which is then diagenetically altered and preserved as the partially saturated okenane. Discovering okenane in sediments is considered evidence of purple sulfur bacteria, implying an anoxic and sulfidic environment.
In the Paleoproterozoic, the water column possibly became sulfidic and anoxic. Purple and green sulfur bacteria likely thrived in this euxinic environment. Purple sulfur bacteria produce the pigment okenone which, during diagenesis, degrades to okenane. Green sulfur bacteria with green pigments produce chlorobactene, which is altered to chlorobactane during burial. Green sulfur bacteria with brown pigments produce isorenieratene, which is preserved as isorenieratane. Each anoxygenic phototroph occupies a different depth range in the ocean, based on their pigment's light absorption. Biomarkers from these species may teach us about anoxic paleoenvironments. Purple and Green Sulfur Bacteria and Their Biomarkers.png
In the Paleoproterozoic, the water column possibly became sulfidic and anoxic. Purple and green sulfur bacteria likely thrived in this euxinic environment. Purple sulfur bacteria produce the pigment okenone which, during diagenesis, degrades to okenane. Green sulfur bacteria with green pigments produce chlorobactene, which is altered to chlorobactane during burial. Green sulfur bacteria with brown pigments produce isorenieratene, which is preserved as isorenieratane. Each anoxygenic phototroph occupies a different depth range in the ocean, based on their pigment's light absorption. Biomarkers from these species may teach us about anoxic paleoenvironments.

Okenone is a carotenoid, [4] a class of pigments ubiquitous across photosynthetic organisms. These conjugated molecules act as accessories in the light harvesting complex. Over 600 carotenoids are known, each with a variety of functional groups that alter their absorption spectrum. Okenone appears to be best adapted to the yellow-green transition (520 nm) of the visible spectrum, capturing light below marine plankton in the ocean. This depth varies based on the community structure of the water column. A survey of microbial blooms found Chromatiaceae anywhere between 1.5m and 24m depth, but more than 75% occurred above 12 meters. [5] Further planktonic sulfur bacteria occupy other niches: green sulfur bacteria, the Chlorobiaceae, that produce the carotenoid chlorobactene were found in greatest abundance above 6m while green sulfur bacteria that produce isorenieratene were predominantly identified above 17m. Finding any of these carotenoids in ancient rocks could constrain the depth of the oxic to anoxic transition as well as confine past ecology. Okenane and chlorobactane discovered in Australian Paleoproterozoic samples allowed conclusions of a temporarily shallow anoxic transition, likely between 12 and 25m. [2]

Okenone is synthesized in 12 species of Chromatiaceae, spanning eight genera. Other purple sulfur bacteria have acyclic carotenoid pigments like lycopene and rhodopin. However, geochemists largely study okenone because it is structurally unique. It is the only pigment with a 2,3,4 trimethylaryl substitution pattern. In contrast, the green sulfur bacteria produce 2,3,6 trimethylaryl isoprenoids. [6] The synthesis of these structures produce biological specificity that can distinguish the ecology of past environments. Okenone, chlorobactene, and isorenieratene are produced by sulfur bacteria through modification of lycopene. In okenone, the end group of lycopene produces a χ-ring, while chlorobactene has a φ-ring. [7] The first step in biosynthesis of these two pigments is similar, formation of a β-ring by a β-cyclase enzyme. Then the syntheses diverge, with carotene desaturase/methyltransferase enzyme transforming the β-ring end group into a χ-ring. Other reactions complete the synthesis to okenone: elongating the conjugation, adding a methoxy group, and inserting a ketone. However, only the first synthetic steps are well characterized biologically.

Preservation

One diagenetic pathway proposed to saturate okenone to okenane is reductive desulphurization, where hydrogen sulfide adds to a double bond and is then removed. More research is needed on other reactions that remove functional groups before preservation. Okenone Reductive Desulphurization to Okenane.png
One diagenetic pathway proposed to saturate okenone to okenane is reductive desulphurization, where hydrogen sulfide adds to a double bond and is then removed. More research is needed on other reactions that remove functional groups before preservation.

Pigments and other biomarkers produced by organisms can evade microbial and chemical degradation and persist in sedimentary rocks. [8] Under conditions of preservation, the environment is often anoxic and reducing, leading to chemical loss of functional groups like double bonds and hydroxyl groups. The exact reactions during diagenesis are poorly understood, although some have proposed reductive desulphurization as a mechanism for saturation of okenone to okenane. [9] [10] There is always the possibility that okenane is created by abiotic reactions, possibly from methyl shifts in β-carotene. [11] If this reaction was occurring, okenane would have multiple precursors and the biological specificity of the biomarker would be diminished. However, it is unlikely that isomer specific rearrangements of two methyl groups are occurring without enzymatic activity. The majority of studies conclude that okenane is a true biomarker of purple sulfur bacteria. However, other biological arguments against this interpretation hold merit. [12] Past organisms that synthesized okenone may not be modern analogues of purple sulfur bacteria. There may also be other okenone producing photosynthesizers in today's ocean that are uncharacterized. A further complication is horizontal gene transfer. [13] If Chromatiaceae gained the ability to create okenone more recently that the Paleoproterozoic, then the okenane does not track purple sulfur bacteria, but rather the original gene donor. These ambiguities indicate that interpretation of biomarkers in billion-year-old rocks will be limited by understanding of ancient metabolisms.

Measurement techniques

GC/MS

Prior to analysis, sedimentary rocks are extracted for organic matter. Typically, only less than one percent is extractable due to the thermal maturity of the source rock. The organic content is often separated into saturates, aromatics, and polars. Gas chromatography can be coupled to mass spectrometry to analyze the extracted aromatic fraction. Compounds elute from the column based on their mass-to-charge ratio (M/Z) and are displayed based on relative intensity. Peaks are assigned to compounds based on library searches, standards, and relative retention times. Some molecules have characteristic peaks that allow easy searches at particular mass-to-charge ratios. For the trimethylaryl isoprenoid okenane this characteristic peak occurs at M/Z of 134.

Isotope ratios

Carbon isotope ratios of purple and green sulfur bacteria are significantly different that other photosynthesizing organisms. The biomass of the purple sulfur bacteria, Chromatiaceae is often depleted in δ13C compared to typical oxygenic phototrophs while the green sulfur bacteria, Chlorobiaceae, are often enriched. [14] This offers an additional discrimination to determine ecological communities preserved in sedimentary rocks. For the biomarker okenane, the δ13C could be determined by an Isotope Ratio Mass Spectrometer.

Case study: Northern Australia

In modern environments, purple sulfur bacteria thrive in meromictic (permanently stratified) lakes [15] and silled fjords and are seen in few marine ecosystems. Hypersaline waters like the Black Sea are exceptions. [16] However, billions of years ago, when the oceans were anoxic and sulfidic, phototrophic sulfur bacteria had more habitable space. Researchers at the Australian National University and the Massachusetts Institute of Technology investigated 1.6-billion-year-old rocks to examine the chemical conditions of the Paleoproterozoic ocean. Many believe that this time had deeply penetrating oxic water columns because of the disappearance of banded iron formations roughly 1.8 billion years ago. Others, spearheaded by Donald Canfield's 1998 Nature paper, believe that waters were euxinic. Examining rocks from the time uncovered biomarkers of both purple and green sulfur bacteria, adding evidence to support the Canfield Ocean hypothesis. The sedimentary outcrop analyzed was the Barney Creek Formation from the McArthur group in northern Australia. Sample analysis identified both the 2,3,6 trimethylarl isoprenoids (chlorobactane) of Chlorobiaceae and the 2,3,4 trimethylaryl isoprenoids (okenane) of Chromatiaceae. Both chlorobactane and okenane indicate a euxinic ocean, with sulfidic and anoxic surface conditions below 12-25m. The authors concluded that although oxygen was in the atmosphere, the Paleoproterozoic oceans were not completely oxygenated. [2]

See also

Related Research Articles

<span class="mw-page-title-main">Green sulfur bacteria</span> Family of bacteria

The green sulfur bacteria, Chlorobiota, are a phylum of obligately anaerobic photoautotrophic bacteria that metabolize sulfur.

The purple sulfur bacteria (PSB) are part of a group of Pseudomonadota capable of photosynthesis, collectively referred to as purple bacteria. They are anaerobic or microaerophilic, and are often found in stratified water environments including hot springs, stagnant water bodies, as well as microbial mats in intertidal zones. Unlike plants, algae, and cyanobacteria, purple sulfur bacteria do not use water as their reducing agent, and therefore do not produce oxygen. Instead, they can use sulfur in the form of sulfide, or thiosulfate (as well, some species can use H2, Fe2+, or NO2−) as the electron donor in their photosynthetic pathways. The sulfur is oxidized to produce granules of elemental sulfur. This, in turn, may be oxidized to form sulfuric acid.

<span class="mw-page-title-main">Purple bacteria</span> Group of phototrophic bacteria

Purple bacteria or purple photosynthetic bacteria are Gram-negative proteobacteria that are phototrophic, capable of producing their own food via photosynthesis. They are pigmented with bacteriochlorophyll a or b, together with various carotenoids, which give them colours ranging between purple, red, brown, and orange. They may be divided into two groups – purple sulfur bacteria and purple non-sulfur bacteria. Purple bacteria are anoxygenic phototrophs widely spread in nature, but especially in aquatic environments, where there are anoxic conditions that favor the synthesis of their pigments.

<span class="mw-page-title-main">Green Lake (New York)</span> Lake in New York

Green Lake is the larger of the two lakes in Green Lakes State Park, which lies about 9 miles (14 km) east of downtown Syracuse in Onondaga County, New York. Round Lake is the smaller lake located west of Green Lake. Both lakes are meromictic, which means no seasonal mixing of surface and bottom waters occurs. Meromictic lakes are fairly rare; they have been extensively studied, in part because their sediments can preserve a historical record extending back thousands of years, and because of the euxinic conditions which can form in the deep water.

<span class="mw-page-title-main">Chromatiaceae</span> Family of purple sulfur bacteria

The Chromatiaceae are one of the two families of purple sulfur bacteria, together with the Ectothiorhodospiraceae. They belong to the order Chromatiales of the class Gammaproteobacteria, which is composed by unicellular Gram-negative organisms. Most of the species are photolithoautotrophs and conduct an anoxygenic photosynthesis, but there are also representatives capable of growing under dark and/or microaerobic conditions as either chemolithoautotrophs or chemoorganoheterotrophs.

Photoheterotrophs are heterotrophic phototrophs – that is, they are organisms that use light for energy, but cannot use carbon dioxide as their sole carbon source. Consequently, they use organic compounds from the environment to satisfy their carbon requirements; these compounds include carbohydrates, fatty acids, and alcohols. Examples of photoheterotrophic organisms include purple non-sulfur bacteria, green non-sulfur bacteria, and heliobacteria. These microorganisms are ubiquitous in aquatic habitats, occupy unique niche-spaces, and contribute to global biogeochemical cycling. Recent research has also indicated that the oriental hornet and some aphids may be able to use light to supplement their energy supply.

<span class="mw-page-title-main">Sulfur cycle</span> Biogeochemical cycle of sulfur

The sulfur cycle is a biogeochemical cycle in which the sulfur moves between rocks, waterways and living systems. It is important in geology as it affects many minerals and in life because sulfur is an essential element (CHNOPS), being a constituent of many proteins and cofactors, and sulfur compounds can be used as oxidants or reductants in microbial respiration. The global sulfur cycle involves the transformations of sulfur species through different oxidation states, which play an important role in both geological and biological processes. Steps of the sulfur cycle are:

<span class="mw-page-title-main">Great Oxidation Event</span> Paleoproterozoic surge in atmospheric oxygen

The Great Oxidation Event (GOE), also called the Great Oxygenation Event, the Oxygen Catastrophe, the Oxygen Revolution, the Oxygen Crisis, or the Oxygen Holocaust, was a time interval during the Early Earth's Paleoproterozoic era when the Earth's atmosphere and the shallow ocean first experienced a rise in the concentration of oxygen. This began approximately 2.460–2.426 Ga (billion years) ago, during the Siderian period, and ended approximately 2.060 Ga, during the Rhyacian. Geological, isotopic, and chemical evidence suggests that biologically-produced molecular oxygen (dioxygen or O2) started to accumulate in Earth's atmosphere and changed it from a weakly reducing atmosphere practically absent of oxygen into an oxidizing one containing abundant free oxygen, with oxygen levels being as high as 10% of their present atmospheric level by the end of the GOE.

γ-Carotene (gamma-carotene) is a carotenoid, and is a biosynthetic intermediate for cyclized carotenoid synthesis in plants. It is formed from cyclization of lycopene by lycopene cyclase epsilon. Along with several other carotenoids, γ-carotene is a vitamer of vitamin A in herbivores and omnivores. Carotenoids with a cyclized, beta-ionone ring can be converted to vitamin A, also known as retinol, by the enzyme beta-carotene 15,15'-dioxygenase; however, the bioconversion of γ-carotene to retinol has not been well-characterized. γ-Carotene has tentatively been identified as a biomarker for green and purple sulfur bacteria in a sample from the 1.640 ± 0.003-Gyr-old Barney Creek Formation in Northern Australia which comprises marine sediments. Tentative discovery of γ-carotene in marine sediments implies a past euxinic environment, where water columns were anoxic and sulfidic. This is significant for reconstructing past oceanic conditions, but so far γ-carotene has only been potentially identified in the one measured sample.

A chemocline is a type of cline, a layer of fluid with different properties, characterized by a strong, vertical chemistry gradient within a body of water. In bodies of water where chemoclines occur, the cline separates the upper and lower layers, resulting in different properties for those layers. The lower layer shows a change in the concentration of dissolved gases and solids compared to the upper layer.

<span class="mw-page-title-main">Anoxygenic photosynthesis</span> Process used by obligate anaerobes

Anoxygenic photosynthesis is a special form of photosynthesis used by some bacteria and archaea, which differs from the better known oxygenic photosynthesis in plants in the reductant used and the byproduct generated.

<span class="mw-page-title-main">Isorenieratene</span> Chemical compound

Isorenieratene /ˌaɪsoʊrəˈnɪərətiːn/ is a carotenoid light harvesting pigment produced exclusively by the genus Chlorobium. Chlorobium are the brown-colored strains of the family of green sulfur bacteria (Chlorobiaceae). Green sulfur bacteria are anaerobic photoautotrophic organisms meaning they perform photosynthesis in the absence of oxygen using hydrogen sulfide in the following reaction:

Chlorobaculum tepidum, previously known as Chlorobium tepidum, is an anaerobic, thermophilic green sulfur bacteria first isolated from New Zealand. Its cells are gram-negative and non-motile rods of variable length. They contain chlorosomes and bacteriochlorophyll a and c.

In some forms of photosynthetic bacteria, a chromatophore is a pigmented(coloured), membrane-associated vesicle used to perform photosynthesis. They contain different coloured pigments.

Crocetane, or 2,6,11,15-tetramethylhexadecane, is an isoprenoid hydrocarbon compound. Unlike its isomer phytane, crocetane has a tail-to-tail linked isoprenoid skeleton. Crocetane has been detected in modern sediments and geological records as a biomarker, often associated with anaerobic methane oxidation.

Euxinia or euxinic conditions occur when water is both anoxic and sulfidic. This means that there is no oxygen (O2) and a raised level of free hydrogen sulfide (H2S). Euxinic bodies of water are frequently strongly stratified, have an oxic, highly productive, thin surface layer, and have anoxic, sulfidic bottom water. The word euxinia is derived from the Greek name for the Black Sea (Εὔξεινος Πόντος (Euxeinos Pontos)) which translates to "hospitable sea". Euxinic deep water is a key component of the Canfield ocean, a model of oceans during the Proterozoic period (known as the Boring Billion) proposed by Donald Canfield, an American geologist, in 1998. There is still debate within the scientific community on both the duration and frequency of euxinic conditions in the ancient oceans. Euxinia is relatively rare in modern bodies of water, but does still happen in places like the Black Sea and certain fjords.

<span class="mw-page-title-main">Microbial oxidation of sulfur</span>

Microbial oxidation of sulfur is the oxidation of sulfur by microorganisms to build their structural components. The oxidation of inorganic compounds is the strategy primarily used by chemolithotrophic microorganisms to obtain energy to survive, grow and reproduce. Some inorganic forms of reduced sulfur, mainly sulfide (H2S/HS−) and elemental sulfur (S0), can be oxidized by chemolithotrophic sulfur-oxidizing prokaryotes, usually coupled to the reduction of oxygen (O2) or nitrate (NO3−). Anaerobic sulfur oxidizers include photolithoautotrophs that obtain their energy from sunlight, hydrogen from sulfide, and carbon from carbon dioxide (CO2).

Chlorobactane is the diagenetic product of an aromatic carotenoid produced uniquely by green-pigmented green sulfur bacteria (GSB) in the order Chlorobiales. Observed in organic matter as far back as the Paleoproterozoic, its identity as a diagnostic biomarker has been used to interpret ancient environments.

<span class="mw-page-title-main">Tetrahymanol</span> Chemical compound

Tetrahymanol is a gammacerane-type membrane lipid first found in the marine ciliate Tetrahymena pyriformis. It was later found in other ciliates, fungi, ferns, and bacteria. After being deposited in sediments that compress into sedimentary rocks over millions of years, tetrahymanol is dehydroxylated into gammacerane. Gammacerane has been interpreted as a proxy for ancient water column stratification.

<span class="mw-page-title-main">Lycopane</span> Chemical compound

Lycopane (C40H82; 2,6,10,14,19,23,27,31-octamethyldotriacontane), a 40 carbon alkane isoprenoid, is a widely present biomarker that is often found in anoxic settings. It has been identified in anoxically deposited lacustrine sediments (such as the Messel formation and the Condor oil shale deposit). It has been found in sulfidic and anoxic hypersaline environments (such as the Sdom Formation). It has been widely identified in modern marine sediments, including the Peru upwelling zone, the Black Sea, and the Cariaco Trench. It has been found only rarely in crude oils.

References

  1. ↑ Imhoff, Johannes F. (1995-01-01). "Taxonomy and Physiology of Phototrophic Purple Bacteria and Green Sulfur Bacteria". In Blankenship, Robert E.; Madigan, Michael T.; Bauer, Carl E. (eds.). Anoxygenic Photosynthetic Bacteria. Advances in Photosynthesis and Respiration. Vol. 2. Springer Netherlands. pp. 1–15. doi:10.1007/0-306-47954-0_1. ISBN   9780792336815.
  2. 1 2 3 Brocks, Jochen J.; Schaeffer, Philippe (2008-03-01). "Okenane, a biomarker for purple sulfur bacteria (Chromatiaceae), and other new carotenoid derivatives from the 1640 Ma Barney Creek Formation". Geochimica et Cosmochimica Acta. 72 (5): 1396–1414. Bibcode:2008GeCoA..72.1396B. doi:10.1016/j.gca.2007.12.006.
  3. ↑ Brocks, Jochen J.; Love, Gordon D.; Summons, Roger E.; Knoll, Andrew H.; Logan, Graham A.; Bowden, Stephen A. (2005). "Biomarker evidence for green and purple sulphur bacteria in a stratified Palaeoproterozoic sea". Nature. 437 (7060): 866–870. Bibcode:2005Natur.437..866B. doi:10.1038/nature04068. PMID   16208367. S2CID   4427285.
  4. ↑ Schaeffer, Philippe; Adam, Pierre; Wehrung, Patrick; Albrecht, Pierre (1997-12-01). "Novel aromatic carotenoid derivatives from sulfur photosynthetic bacteria in sediments". Tetrahedron Letters. 38 (48): 8413–8416. doi:10.1016/S0040-4039(97)10235-0.
  5. ↑ Gemerden, Hans Van; Mas, Jordi (1995-01-01). Blankenship, Robert E.; Madigan, Michael T.; Bauer, Carl E. (eds.). Anoxygenic Photosynthetic Bacteria. Advances in Photosynthesis and Respiration. Springer Netherlands. pp. 49–85. doi:10.1007/0-306-47954-0_4. ISBN   9780792336815.
  6. ↑ Summons, R. E.; Powell, T. G. (1987-03-01). "Identification of aryl isoprenoids in source rocks and crude oils: Biological markers for the green sulphur bacteria". Geochimica et Cosmochimica Acta. 51 (3): 557–566. Bibcode:1987GeCoA..51..557S. doi:10.1016/0016-7037(87)90069-X.
  7. ↑ Vogl, K.; Bryant, D. A. (2012-05-01). "Biosynthesis of the biomarker okenone: χ-ring formation". Geobiology. 10 (3): 205–215. Bibcode:2012Gbio...10..205V. doi:10.1111/j.1472-4669.2011.00297.x. ISSN   1472-4669. PMID   22070388. S2CID   205627793.
  8. ↑ Brocks, Jochen J.; Grice, Kliti (2011-01-01). Reitner, Joachim; Thiel, Volker (eds.). Encyclopedia of Geobiology. Encyclopedia of Earth Sciences Series. Springer Netherlands. pp. 147–167. doi:10.1007/978-1-4020-9212-1_30. ISBN   9781402092114.
  9. ↑ Hebting, Y.; Schaeffer, P.; Behrens, A.; Adam, P.; Schmitt, G.; Schneckenburger, P.; Bernasconi, S. M.; Albrecht, P. (2006-06-16). "Biomarker Evidence for a Major Preservation Pathway of Sedimentary Organic Carbon". Science. 312 (5780): 1627–1631. Bibcode:2006Sci...312.1627H. doi:10.1126/science.1126372. ISSN   0036-8075. PMID   16690819. S2CID   45660326.
  10. ↑ Werne, Josef P.; Lyons, Timothy W.; Hollander, David J.; Schouten, Stefan; Hopmans, Ellen C.; Sinninghe Damsté, Jaap S. (2008-07-15). "Investigating pathways of diagenetic organic matter sulfurization using compound-specific sulfur isotope analysis". Geochimica et Cosmochimica Acta. 72 (14): 3489–3502. Bibcode:2008GeCoA..72.3489W. doi:10.1016/j.gca.2008.04.033.
  11. ↑ Koopmans, Martin P.; Schouten, Stefan; Kohnen, Math E. L.; Sinninghe Damsté, Jaap S. (1996-12-01). "Restricted utility of aryl isoprenoids as indicators for photic zone anoxia". Geochimica et Cosmochimica Acta. 60 (23): 4873–4876. Bibcode:1996GeCoA..60.4873K. doi:10.1016/S0016-7037(96)00303-1. hdl: 1874/4427 .
  12. ↑ Brocks, Jochen J.; Banfield, Jillian (2009). "Unravelling ancient microbial history with community proteogenomics and lipid geochemistry". Nature Reviews Microbiology. 7 (8): 601–609. doi:10.1038/nrmicro2167. PMID   19609261. S2CID   20913191.
  13. ↑ Cobbs, Cassidy; Heath, Jeremy; Stireman III, John O.; Abbot, Patrick (2013-08-01). "Carotenoids in unexpected places: Gall midges, lateral gene transfer, and carotenoid biosynthesis in animals". Molecular Phylogenetics and Evolution. 68 (2): 221–228. doi:10.1016/j.ympev.2013.03.012. PMID   23542649.
  14. ↑ Zyakun, A. M.; Lunina, O. N.; Prusakova, T. S.; Pimenov, N. V.; Ivanov, M. V. (2009-12-06). "Fractionation of stable carbon isotopes by photoautotrophically growing anoxygenic purple and green sulfur bacteria". Microbiology. 78 (6): 757. doi:10.1134/S0026261709060137. ISSN   0026-2617. S2CID   34430255.
  15. ↑ Overmann, Jörg; Beatty, J. Thomas; Hall, Ken J.; Pfennig, Norbert; Northcote, Tom G. (1991-07-01). "Characterization of a dense, purple sulfur bacterial layer in a meromictic salt lake" (PDF). Limnology and Oceanography. 36 (5): 846–859. Bibcode:1991LimOc..36..846O. doi: 10.4319/lo.1991.36.5.0846 . ISSN   1939-5590.
  16. ↑ Hashwa, F. A.; Trüper, H. G. (1978). "Viable phototrophic sulfur bacteria from the Black-Sea bottom". Helgoländer Wissenschaftliche Meeresuntersuchungen. 31 (1–2): 249–253. Bibcode:1978HWM....31..249H. doi: 10.1007/BF02297000 . ISSN   0017-9957.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.