Name: bacterial light capture without oxygen
Uploaded: 2025-06-12T09:36:37.000Z
Duration: 1 min 30 s
Channel: JoVE

Anoxygenic photosynthesis is a light-driven process in purple and green sulfur bacteria that converts carbon dioxide and alternate electron donors, such as hydrogen sulfide, into organic compounds without producing oxygen.Anoxygenic phototrophs operate with a single photosystem and rely on bacteriochlorophyll pigments located in the chromatophores, chlorosomes, or cytoplasmic membranes.In purple bacteria, the P870 reaction center excites electrons, transferring them through bacteriopheophytin to a quinone pool, iron-sulfur cluster proteins, and cytochromes, ultimately returning them to the reaction center.This electron transfer process generates the proton motive force for ATP synthesis.Additionally, these bacteria use reverse electron flow, powered by the proton motive force, to reduce NAD+ using external electron donors like hydrogen sulfide or elemental sulfur.Green sulfur bacteria, with P840 as their reaction center, transfer electrons via bacteriochlorophylls, FeS cluster proteins, quinones, and cytochromes.These bacteria use ferredoxins to directly reduce NAD+ to NADH, bypassing the reverse electron flow.

atp-synthase

Anoxygenic Photosynthesis

Anoxygene fotosynthese is een fototroof proces waarbij lichtenergie wordt vastgelegd om koolstofvastlegging aan te drijven zonder de productie van moleculaire zuurstof. In tegenstelling tot oxygene fotosynthese, die water als elektrondonor gebruikt en zuurstof vrijgeeft, maken anoxygene fototrofen gebruik van alternatieve elektrondonoren zoals waterstofsulfide (H_2S), elementaire zwavel (S&#8304;) of thiosulfaat (S_2O_3^2-). Dit proces wordt uitgevoerd door diverse groepen bacteri&#235;n, waaronder paarse bacteri&#235;n, groene zwavelbacteri&#235;n, heliobacteri&#235;n en andere anoxygene fototrofen, die gespecialiseerde fotosynthetische mechanismen hebben ontwikkeld op basis van een enkel fotosysteem.
Verschillen tussen oxygene en anoxygene fotosynthese
Oxygene en anoxygene fotosynthese verschillen voornamelijk in elektrondonoren, zuurstofproductie en de samenstelling van het fotosysteem. Oxygene fotosynthese, uitgevoerd door cyanobacteri&#235;n, algen en planten, gebruikt water (H_2O) als elektrondonor, wat leidt tot de productie van zuurstof (O_2) als bijproduct. Het werkt met twee fotosystemen (PSI en PSII), gerangschikt in een Z-schema, waarmee de directe reductie van NADP&#8314; tot NADPH mogelijk is. Anoxygene fotosynthese daarentegen vertrouwt op alternatieve elektrondonoren zoals waterstofsulfide of organische verbindingen en geeft geen zuurstof af. Het functioneert met een enkel fotosysteem, waarbij voornamelijk gebruik wordt gemaakt van cyclische elektronenstroom voor ATP-synthese. Sommige bacteri&#235;n vereisen omgekeerde elektronenstroom om reducerend vermogen op te wekken. Bovendien gebruiken anoxygene fototrofen bacteriochlorofyllen in plaats van chlorofyllen, waardoor ze in staat zijn infrarood licht te absorberen en te overleven in anaerobe of microaerofiele omgevingen.
Fotosystemen en elektronentransport
Anoxygene fototrofen maken gebruik van bacteriochlorofylpigmenten om lichtenergie te absorberen. Deze pigmenten bevinden zich in specifieke cellulaire structuren: chromatoforen bij paarse bacteri&#235;n, chlorosomen bij groene zwavelbacteri&#235;n en andere gespecialiseerde membraangeassocieerde structuren bij heliobacteri&#235;n. De energie die door deze pigmenten wordt geabsorbeerd, wekt elektronen op in gespecialiseerde reactiecentra&#8212;P870 bij paarse niet-zwavelbacteri&#235;n, P840 bij groene zwavelbacteri&#235;n, en variaties bij andere anoxygene fototrofen.
Bij paarse bacteri&#235;n worden de ge&#235;xciteerde elektronen van het P870-reactiecentrum opeenvolgend getransporteerd via bacteriofeofytine, een quinonpool, ijzer-zwavel (FeS) cluster-eiwitten en cytochromen, voordat ze terugkeren naar het reactiecentrum. Deze cyclische elektronenstroom genereert een protonengradi&#235;nt over het membraan, wat leidt tot ATP-synthese via chemiosmose. Daarnaast hebben paarse bacteri&#235;n een externe elektrondonor nodig, zoals waterstofsulfide, om NAD^+ te reduceren tot NADH. Deze reductie wordt bereikt via omgekeerde elektronenstroom, die extra energie nodig heeft van de protonmotorkracht.
Groene zwavelbacteri&#235;n hanteren een ander mechanisme voor elektronenoverdracht. Het P840-reactiecentrum doneert hoogenergetische elektronen aan een reeks acceptoren, waaronder bacteriochlorofyllen, FeS-cluster-eiwitten, quinonen en cytochromen. In tegenstelling tot paarse bacteri&#235;n gebruiken groene zwavelbacteri&#235;n echter ferredoxinen, die elektronen rechtstreeks overdragen aan NAD^+, waarbij NADH wordt gevormd zonder dat omgekeerde elektronenstroom nodig is. Deze effici&#235;ntie stelt groene zwavelbacteri&#235;n in staat om te overleven in omgevingen met weinig licht, zoals diepzeehydrothermale bronnen en gelaagde meren.
Diversiteit van anoxygene fototrofen
Naast paarse en groene zwavelbacteri&#235;n voeren andere bacteriegroepen anoxygene fotosynthese uit. Heliobacteri&#235;n, behorend tot het fylum Firmicutes, gebruiken een enkel fotosysteem met bacteriochlorofyl g. In tegenstelling tot andere anoxygene fototrofen missen zij uitgebreide interne membranen en voeren zij fotosynthese uit in het cytoplasmatische membraan. Chloroflexi, ook wel groene niet-zwavelbacteri&#235;n genoemd, combineren fototrofe en heterotrofe metabolisme, waardoor zij kunnen overleven in uiteenlopende ecologische niches.
Ecologische en evolutionaire betekenis
Anoxygene fotosynthese speelt een cruciale rol in wereldwijde biogeochemische cycli door koolstof- en zwaveltransformaties aan te drijven in anaerobe omgevingen. Deze bacteri&#235;n dragen bij aan de primaire productie in zuurstofarme ecosystemen en worden beschouwd als evolutionaire voorlopers van moderne oxygene fototrofen. Het vermogen van verschillende bacteriegroepen om een verscheidenheid aan elektrondonoren te gebruiken, suggereert dat het vroege fotosynthetische leven op aarde onder anoxygene omstandigheden functioneerde v&#243;&#243;r de opkomst van zuurstofproducerende fotosynthese via wateroxidatie. Bovendien stelt de aanpassing van bacteriochlorofyllen om infrarood en zwak licht te absorberen deze bacteri&#235;n in staat om te gedijen in omgevingen waar oxygene fototrofen niet kunnen concurreren, zoals diepe wateren, sedimenten en hydrothermale systemen.

ATP-synthase

Anoxygene fotosynthese is een fototroof proces waarbij lichtenergie wordt vastgelegd om koolstofvastlegging aan te drijven zonder de productie van ...

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bacterial light capture without oxygen

Anoxygenic photosynthesis is a bacterial way to capture light energy without making oxygen. It supports carbon fixation, but it does not use water as the electron donor. Instead, these phototrophs use other electron donors such as hydrogen sulfide, elemental sulfur, thiosulfate, or organic compounds.

This process is carried out by several groups of bacteria, including purple bacteria, green sulfur bacteria, heliobacteria, and other anoxygenic phototrophs. These organisms have evolved a photosynthetic system built around a single photosystem. That is different from oxygenic photosynthesis in plants, algae, and cyanobacteria, which uses water and releases oxygen.

Oxygenic and anoxygenic photosynthesis also differ in how electrons move. Oxygenic photosynthesis uses two photosystems, PSI and PSII, in a Z-scheme that directly reduces NADP+ to NADPH. Anoxygenic photosynthesis usually depends on cyclic electron flow to make ATP, and some bacteria also need reverse electron transport to build reducing power. Bacteriochlorophylls, not chlorophylls, absorb the light in these bacteria. This lets them use infrared light and live in anaerobic or microaerophilic settings.

The light-absorbing pigments are arranged in special cell structures. Purple bacteria place them in chromatophores, green sulfur bacteria use chlorosomes, and heliobacteria use other membrane-linked structures. Light excites electrons in reaction centers such as P870 in purple nonsulfur bacteria and P840 in green sulfur bacteria. The exact reaction center can vary in other anoxygenic phototrophs.

In purple bacteria, electrons move from P870 through bacteriopheophytin, a quinone pool, iron-sulfur cluster proteins, and cytochromes before returning to the reaction center. This cyclic path builds a proton gradient across the membrane. Chemiosmosis then uses that gradient to make ATP. Purple bacteria still need an outside electron donor, such as hydrogen sulfide, to reduce NAD+ to NADH. They do this by reverse electron flow, which costs energy from the proton motive force.

Green sulfur bacteria use a different electron transport route. Their P840 reaction center passes electrons to bacteriochlorophylls, FeS cluster proteins, quinones, and cytochromes. They also use ferredoxins, which can transfer electrons directly to NAD+ to form NADH. Because they do not need reverse electron flow for this step, they can live well in very low light. Examples include deep-sea hydrothermal vents and stratified lakes.

Other bacterial groups also carry out anoxygenic photosynthesis. Heliobacteria, which belong to the Firmicutes phylum, use bacteriochlorophyll g and a single photosystem in the cytoplasmic membrane. They do not have extensive internal membranes like some other phototrophs. Chloroflexi, also called green nonsulfur bacteria, can use both phototrophic and heterotrophic metabolism, which helps them survive in a range of niches.

Anoxygenic photosynthesis matters in both ecology and evolution. It helps drive carbon and sulfur cycles in anaerobic environments and supports primary production where oxygen is limited. These bacteria are also thought to be evolutionary precursors to modern oxygenic phototrophs. Their ability to use different electron donors and absorb low-intensity infrared light helps them thrive in places where oxygenic phototrophs cannot compete, such as deep waters, sediments, and hydrothermal systems.

Bacterial Light Capture Without Oxygen

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chemiosmosis and atp synthesis

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respiration pathways

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microbial fermentation

Fermentation Products in Microbes

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Microbes Use Proteins for Energy

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oxygenic photosynthesis

How Plants Make Oxygen and ATP

Oxygenic photosynthesis is the process plants, algae, and cyanobacteria use to capture light energy and turn it into chemical energy. It uses water as the source of electrons and releases molecular oxygen, or O2. The process also produces ATP and NADPH, which cells need for later energy use and carbon fixation. The main reactions happen in the thylakoid membranes, where chlorophyll pigments absorb light. In cyanobacteria, these membranes come from folds in the plasma membrane. Two photosystems...

anoxygenic photosynthesis

Anoxygenic photosynthesis is a bacterial way to capture light energy without making oxygen. It supports carbon fixation, but it does not use water as the electron donor. Instead, these phototrophs use other electron donors such as hydrogen sulfide, elemental sulfur, thiosulfate, or organic compounds. This process is carried out by several groups of bacteria, including purple bacteria, green sulfur bacteria, heliobacteria, and other anoxygenic phototrophs. These organisms have evolved a...

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biosynthesis of polysaccharides

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Nitrogen Uptake by Microbes

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Amino Acid Building from Cell Metabolites

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key terms and concepts

Explore how purple bacteria, green sulfur bacteria, and other phototrophs use light without releasing oxygen, and compare their electron transport systems.

Bacterial Light Capture Without Oxygen | JoVE K12

JoVE Core Microbiology provides an engaging introduction to the microbial world and its influence on health, industry, and the environment. This comprehensive collection covers key concepts such as microbial structure, metabolism, genetics, and ecology. It introduces essential laboratory techniques and microscopy methods through visually engaging animations. Corresponding scientist-in-action videos bridge classroom concepts with real-world research and applications.

microbiology

Bacterial Light Capture Without Oxygen

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