“Purple bacteria”的意思、由来-开放百科全书

Purple bacteria are mainly photoautotrophic, but are also known to be chemoautotrophic and photoheterotrophic. They can be mixotrophs, capable of aerobic respiration and fermentation.^[4]

Location

Photosynthesis occurs at reaction centers on the cell membrane, where the photosynthetic pigments (i.e. bacteriochlorophyll, carotenoids) and pigment-binding proteins are invaginated to form vesicle sacs, tubules, or single-paired or stacked lamellar sheets.^[5]^[6] This is called the intracytoplasmic membrane (ICM) which has increased surface area to maximize light absorption.

Mechanism

Purple bacteria use cyclic electron transport driven by a series of redox reactions.^[7] Light-harvesting complexes surrounding a reaction centre (RC) harvest photons in the form of resonance energy, exciting chlorophyll pigments P870 or P960 located in the RC. Excited electrons are cycled from P870 to quinones Q_A and Q_B, then passed to cytochrome bc₁, cytochrome c₂, and back to P870. The reduced quinone Q_B attracts two cytoplasmic protons and becomes QH₂, eventually being oxidized and releasing the protons to be pumped into the periplasm by the cytochrome bc₁ complex.^[6]^[8] The resulting charge separation between the cytoplasm and periplasm generates a proton motive force used by ATP synthase to produce ATP energy.^[9]^[10]

Electron donors for anabolism

Purple bacteria also transfer electrons from external electron donors directly to cytochrome bc₁ to generate NADH or NADPH used for anabolism.^[11] They are anoxygenic because they do not use water as an electron donor to produce oxygen. One type of purple bacteria, called purple sulfur bacteria (PSB), use sulfide or sulfur as electron donors.^[12] Another type, called purple non-sulfur bacteria, typically use hydrogen as an electron donor but can also use sulfide or organic compounds at lower concentrations compared to PSB.

Purple bacteria lack external electron carriers to spontaneously reduce NAD(P)⁺ to NAD(P)H, so they must use their reduced quinones to endergonically reduce NAD(P)+. This process is driven by the proton motive force and is called reverse electron flow.^[11]

History

Purple bacteria were the first bacteria discovered to photosynthesize without having an oxygen byproduct. Instead, their byproduct is sulfur. This was demonstrated by first establishing the bacteria's reactions to different concentrations of oxygen. What was found was that the bacteria moved quickly away from even the slightest trace of oxygen. Then a dish of the bacteria was taken, and a light was focused on one part of the dish leaving the rest dark. As the bacteria cannot survive without light, all the bacteria moved into the circle of light, becoming very crowded. If the bacteria's byproduct was oxygen, the distances between individuals would become larger and larger as more oxygen was produced. But because of the bacteria's behavior in the focused light, it was concluded that the bacteria's photosynthetic byproduct could not be oxygen.

Evolution

Researchers have theorized that some purple bacteria are related to the mitochondria, symbiotic bacteria in plant and animal cells today that act as organelles. Comparisons of their protein structure suggests that there is a common ancestor.^[13]

Taxonomy

Purple non-sulfur bacteria are found among the alpha and beta subgroups, including:

Purple sulfur bacteria are included among the gamma subgroup, and make up the order Chromatiales. The similarity between the photosynthetic machinery in these different lines indicates it had a common origin, either from some common ancestor or passed by lateral transfer.

References

1. ^{{cite journal|author=D.A. Bryant & N.-U. Frigaard|date=November 2006|title=Prokaryotic photosynthesis and phototrophy illuminated|journal=Trends Microbiol.|volume=14|issue=11|pages=488–96|doi=10.1016/j.tim.2006.09.001|pmid=16997562}}
2. ^{{cite web|url=https://www.sciencedaily.com/releases/2018/11/181113080903.htm |title=Purple bacteria 'batteries' turn sewage into clean energy |author= |date=November 13, 2018 |website=Science Daily |publisher= |access-date=November 14, 2018 |quote=}}
3. ^{{cite web|url=https://www.frontiersin.org/articles/10.3389/fenrg.2018.00107/full |title=Biological and Bioelectrochemical Systems for Hydrogen Production and Carbon Fixation Using Purple Phototrophic Bacteria |authors=Ioanna A. Vasiliadou|display-authors=etal|date=13 November 2018 |website=FrontiersIn.org |publisher= |access-date=14 November 2018 |quote=}}
4. ^{{cite journal|author1=A. A. Tsygankov|author2=A. N. Khusnutdinova|title=Hydrogen in metabolism of purple bacteria and prospects of practical application|journal=Microbiology|date=January 2015|volume=84|issue=1|pages=1–22|doi=10.1134/S0026261715010154}}
5. ^{{Cite web|url=https://www.researchgate.net/publication/225649180|title=Structure, Function and Formation of Bacterial Intracytoplasmic Membranes|website=ResearchGate|language=en|access-date=2017-10-08}}
6. ^¹{{cite journal|author1=Alastair G. McEwan|title=Photosynthetic electron transport and anaerobic metabolism in purple non-sulfur phototrophic bacteria|journal=Antonie van Leeuwenhoek|date=March 1994|volume=66|issue=1–3|pages=151–164|doi=10.1007/BF00871637}}
7. ^{{Cite journal|last=Klamt|first=Steffen|last2=Grammel|first2=Hartmut|last3=Straube|first3=Ronny|last4=Ghosh|first4=Robin|last5=Gilles|first5=Ernst Dieter|date=2008-01-15|title=Modeling the electron transport chain of purple non-sulfur bacteria|journal=Molecular Systems Biology|volume=4|pages=156|doi=10.1038/msb4100191|issn=1744-4292|pmc=2238716|pmid=18197174}}
8. ^{{cite journal|author1=Cogdell, Richard J|author2=Gall, Andrew|author3=Köhler, Jürgen|title=The architecture andfunction of the light-harvesting apparatus of purple bacteria: from singlemolecules to in vivomembranes|journal=Quarterly Reviews of Biophysics|date=August 2006|volume=39|issue=3|pages=227–324|doi=10.1017/S0033583506004434|pmid=17038210|url=https://search.proquest.com/openview/13232d7ed817133145ca93359068ecae/1?pq-origsite=gscholar&cbl=47475|accessdate=8 October 2017}}
9. ^{{Cite book|title=Molecular mechanisms of photosynthesis|last=E.|first=Blankenship, Robert|date=2002|publisher=Blackwell Science|isbn=9780632043217|location=Oxford|oclc=49273347}}
10. ^{{Cite journal|last=Hu|first=Xiche|last2=Damjanović|first2=Ana|last3=Ritz|first3=Thorsten|last4=Schulten|first4=Klaus|date=1998-05-26|title=Architecture and mechanism of the light-harvesting apparatus of purple bacteria|url=http://www.pnas.org/content/95/11/5935|journal=Proceedings of the National Academy of Sciences|language=en|volume=95|issue=11|pages=5935–5941|issn=0027-8424|pmid=9600895|doi=10.1073/pnas.95.11.5935|pmc=34498}}
11. ^¹{{Cite web|url=https://search.proquest.com/openview/13232d7ed817133145ca93359068ecae/1?pq-origsite=gscholar&cbl=47475|title=The architecture and function of the light-harvesting apparatus of purple bacteria: from single molecules to in vivo membranes - ProQuest|website=search.proquest.com|language=en|access-date=2017-10-08}}
12. ^{{Cite journal|last=Basak|first=Nitai|last2=Das|first2=Debabrata|date=2007-01-01|title=The Prospect of Purple Non-Sulfur (PNS) Photosynthetic Bacteria for Hydrogen Production: The Present State of the Art|journal=World Journal of Microbiology and Biotechnology|language=en|volume=23|issue=1|pages=31–42|doi=10.1007/s11274-006-9190-9|issn=0959-3993}}
13. ^{{cite journal|last1=Bui|first1=E. T.|last2=Bradley|first2=P. J.|last3=Johnson|first3=P. J.|url=http://www.pnas.org/content/93/18/9651.full.pdf+html|title=A Common Evolutionary Origin for Mitochondria and Hydrogenosomes|journal=Proceedings of the National Academy of Sciences of the United States of America|date=3 September 1996|volume=93|issue=18|pages=9651–9656|doi=10.1073/pnas.93.18.9651|pmid=8790385|pmc=38483}}