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.

anoxygenic photosynthesis

Anoxygenic Photosynthesis

Anoxygenic photosynthesis is a phototrophic process that captures light energy to drive carbon fixation without producing molecular oxygen. Unlike oxygenic photosynthesis, which utilizes water as an electron donor and releases oxygen, anoxygenic phototrophs use alternative electron donors such as hydrogen sulfide (H&#8322;S), elemental sulfur (S&#8304;), or thiosulfate (S&#8322;O&#8323;&#178;&#8315;). This process is carried out by diverse groups of bacteria, including purple bacteria, green sulfur bacteria, heliobacteria, and other anoxygenic phototrophs, which have evolved specialized photosynthetic mechanisms using a single photosystem.Differences Between Oxygenic and Anoxygenic PhotosynthesisOxygenic and anoxygenic photosynthesis differ primarily in electron donors, oxygen production, and photosystem composition. Oxygenic photosynthesis, carried out by cyanobacteria, algae, and plants, uses water (H&#8322;O) as an electron donor, leading to oxygen (O&#8322;) generation as a byproduct. It operates with two photosystems (PSI and PSII) arranged in a Z-scheme, allowing the direct reduction of NADP&#8314; to NADPH. In contrast, anoxygenic photosynthesis relies on alternative electron donors such as hydrogen sulfide or organic compounds and does not release oxygen. It functions with a single photosystem, primarily utilizing cyclic electron flow for ATP synthesis, with some bacteria requiring reverse electron transport to generate reducing power. Additionally, anoxygenic phototrophs use bacteriochlorophylls instead of chlorophylls, enabling them to absorb infrared light and thrive in anaerobic or microaerophilic environments.Photosystems and Electron TransportAnoxygenic phototrophs rely on bacteriochlorophyll pigments to absorb light energy. These pigments are localized in distinct cellular structures: chromatophores in purple bacteria, chlorosomes in green sulfur bacteria, and other specialized membrane-associated structures in heliobacteria. The energy absorbed by these pigments excites electrons in specialized reaction centers&#8212;P870 in purple nonsulfur bacteria, P840 in green sulfur bacteria, and variations in other anoxygenic phototrophs.In purple bacteria, the excited electrons from the P870 reaction center are transferred sequentially through bacteriopheophytin, a quinone pool, iron-sulfur (FeS) cluster proteins, and cytochromes before returning to the reaction center. This cyclic electron flow generates a proton gradient across the membrane, leading to ATP synthesis via chemiosmosis. Additionally, purple bacteria require an external electron donor, such as hydrogen sulfide, to reduce NAD&#8314; to NADH. This reduction is achieved through reverse electron flow, which requires additional energy input from the proton motive force.Green sulfur bacteria operate with a different electron transport mechanism. The P840 reaction center donates high-energy electrons to a series of acceptors, including bacteriochlorophylls, FeS cluster proteins, quinones, and cytochromes. However, unlike purple bacteria, green sulfur bacteria utilize ferredoxins, which directly transfer electrons to NAD&#8314;, forming NADH without requiring reverse electron flow. This efficiency allows green sulfur bacteria to thrive in low-light environments, such as deep-sea hydrothermal vents and stratified lakes.Diversity of Anoxygenic PhototrophsBesides purple and green sulfur bacteria, other bacterial groups perform anoxygenic photosynthesis. Heliobacteria, belonging to the Firmicutes phylum, use a single photosystem with bacteriochlorophyll g. Unlike other anoxygenic phototrophs, they lack extensive internal membranes and perform photosynthesis in the cytoplasmic membrane. Chloroflexi, also known as green nonsulfur bacteria, employ a mix of phototrophic and heterotrophic metabolism, allowing them to survive in diverse ecological niches.Ecological and Evolutionary SignificanceAnoxygenic photosynthesis is crucial in global biogeochemical cycles by driving carbon and sulfur transformations in anaerobic environments. These bacteria contribute to primary production in oxygen-limited ecosystems and are considered evolutionary precursors to modern oxygenic phototrophs. The ability of different bacterial groups to utilize a variety of electron donors suggests that early photosynthetic life on Earth may have operated under anoxygenic conditions before the advent of water-splitting oxygenic photosynthesis. Furthermore, adapting bacteriochlorophylls to absorb infrared and low-intensity light enables these bacteria to thrive in environments where oxygenic phototrophs cannot compete, such as deep waters, sediments, and hydrothermal systems.

Anoxygenic photosynthesis is a phototrophic process that captures light energy to drive carbon fixation without producing molecular oxygen. Unlike ...

Education

JoVE Core

Microbiology

Unit

Microbial Metabolism

KEY TERMS AND CONCEPTS

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

microbial nutrition

Microbial Energy and Carbon Sources

Microbial energy and carbon sources determine how microorganisms live and grow. These metabolic strategies help microbes survive in many habitats and keep energy moving through ecosystems. They also support nutrient cycling in nature. Microbes are grouped by where they get energy, electrons, and carbon. Phototrophs use light, while chemotrophs use chemical compounds for energy. Lithotrophs take electrons from reduced inorganic substances, and organotrophs take them from organic compounds.

atp and energy production

How Cells Make and Use ATP

ATP is the main energy carrier in cells. It is made of adenosine, which includes adenine and ribose, plus three phosphate groups. The bonds between the phosphate groups hold a large amount of potential energy. When ATP is hydrolyzed, it becomes ADP or AMP and releases energy for cell work. Cells use that energy for many essential tasks. It supports macromolecule synthesis, intracellular transport, and mechanical movement. ATP also acts as an energy manager by linking catabolic and anabolic...

redox reactions

Electron Carriers in Redox Metabolism

Redox reactions move electrons through metabolic pathways in cells. Oxidation is the loss of electrons, and reduction is the gain of electrons. These two steps happen together, which keeps electron flow moving through metabolism. A clear example appears in bacterial metabolism. Glucose is oxidized to carbon dioxide, while oxygen is reduced to water. This shows how one molecule loses electrons as another gains them. Cells use special electron carriers to make these transfers happen.

introduction to metabolism

Metabolism: Energy Use and Biomolecule Synthesis

Metabolism is the set of chemical reactions that keep living cells working. It includes reactions that break down biomolecules and reactions that build them up. These two sides of metabolism work together to support energy balance and cell function. Catabolic pathways break large molecules into smaller parts. Carbohydrates, lipids, and proteins can be broken down into monosaccharides, fatty acids, and amino acids. These reactions release energy, and cells store much of that energy as ATP, or...

carbohydrate catabolism

Glucose Breakdown and ATP Production

Glucose breakdown is a key part of cell metabolism that lets cells make ATP, the usable form of energy. The process follows two main paths: cellular respiration and fermentation. Both start with glycolysis, which does not require oxygen. Glycolysis splits one glucose molecule into two molecules of pyruvic acid. It also produces a net gain of two ATP molecules and two NADH molecules. This step sets up the cell to continue with respiration or switch to fermentation, depending on whether oxygen...

glycolysis

Glycolysis and Pyruvate Fate

Glycolysis is a central pathway in glucose catabolism and a major way cells make energy. It is also called the Embden-Meyerhof pathway. This process takes place in the cytoplasm and can work with or without oxygen, which makes it useful in many organisms and conditions. Glycolysis has ten steps and turns one glucose molecule into two pyruvate molecules. It has two phases. In the preparatory phase, the cell uses two ATP to add phosphate groups to glucose and split it into two three-carbon...

other glycolytic pathways

Pentose Phosphate Pathway and Entner-Doudoroff

The pentose phosphate pathway works alongside glycolysis in cells that need both sugar breakdown and building blocks for growth. It handles pentoses, which are five-carbon sugars, and also uses glucose as a starting point. The pathway has two parts, an oxidative phase and a non-oxidative phase. It does not make ATP directly, but its products can feed back into glycolysis when the cell needs them. The oxidative phase mainly makes NADPH, a reduced electron carrier. In this phase,...

cellular respiration

Cellular Respiration: ATP Production Pathways

Cellular respiration is the process cells use to turn glucose into ATP, the main energy molecule in the cell. It depends on oxidation and the transfer of electrons to a separate electron acceptor. This sequence of reactions supports energy production in both aerobic and anaerobic settings. Glycolysis is the first step. It takes place in the cytoplasm of both prokaryotic and eukaryotic cells. One glucose molecule is broken into two pyruvate molecules, and the cell gains a net 2 ATP and 2 NADH.

electron transport chain components

Electron Transport Chain and ATP Production

The electron transport chain helps cells make ATP by moving electrons through membrane protein complexes. In eukaryotic cells, it sits in the inner mitochondrial membrane. In prokaryotic cells, it is found in the plasma membrane and can differ in the number and type of complexes, depending on the organism and its environment. The chain uses several electron carriers to pass electrons along in redox reactions, which are reactions that involve oxidation and reduction. These carriers include...

chemiosmosis and atp synthesis

Electron Transport Chain Powers ATP Output

The electron transport chain powers ATP production during cellular respiration. It sits in the inner mitochondrial membrane and moves high-energy electrons from NADH and FADH2 to molecular oxygen, the final electron acceptor. As electrons move through the chain, protons are pushed across the membrane to build the gradient needed for ATP synthesis. Electrons from NADH enter the chain at Complex I, also called NADH: ubiquinone oxidoreductase. In prokaryotes, this step helps pump protons from the...

respiration pathways

TCA Cycle and Energy Pathways

Cellular respiration uses the TCA cycle, also called the Krebs cycle, to help cells make usable energy from organic molecules. This pathway is a central part of aerobic respiration and also supports biosynthesis. It links the breakdown of food molecules to the cell's energy needs. Pyruvate from glycolysis enters this process first. The pyruvate dehydrogenase complex converts pyruvate into acetyl-CoA through oxidative decarboxylation. This step produces one NADH and one carbon dioxide molecule.

microbial fermentation

Fermentation Products in Microbes

Fermentation is an anaerobic process that lets microbes make energy from sugar without oxygen or an electron transport chain. It is important in both biology and industry. The process is grouped by the products it makes. Pyruvate and its derivatives act as key electron acceptors in fermentative pathways. This step helps oxidize NADH back to NAD+, which is needed for glycolysis to keep running. Without NAD+ regeneration, glycolysis would stop and the cell would lose its main source of ATP under...

metabolism of chemolithotrophs

How Chemolithotrophs Make ATP

Chemolithotrophs make ATP by using inorganic chemicals as an energy source. They oxidize molecules such as hydrogen gas, ammonia, reduced sulfur compounds, and ferrous iron. Instead of relying on organic carbon like heterotrophs, they move electrons from these inorganic donors into the electron transport chain, or ETC. That electron flow builds a proton motive force, or PMF. The PMF drives ATP synthesis through oxidative phosphorylation. Because inorganic electron donors usually release less...

amino acid catabolism

Microbes Use Proteins for Energy

Microbes can use proteins as a carbon and energy source, especially when polysaccharides or lipids are scarce. But proteins are too large to pass through the plasma membrane on their own. To solve this, microbes secrete extracellular proteases and peptidases that break proteins into peptides. The peptides are then transported into the cell, where intracellular proteases cut them into free amino acids. Once amino acids are available, microbes break them down in two main ways: deamination and...

lipid catabolism

How Microbes Break Down Fats for Energy

Microbes break down triglycerides and fatty acids to make energy. Triglycerides are important long-term energy storage molecules in microorganisms. Lipases hydrolyze, or split with water, triglycerides into glycerol and free fatty acids. Each product then enters a different metabolic route that helps the cell make ATP, the main energy currency. Glycerol metabolism begins after glycerol is released from triglyceride hydrolysis. Glycerol kinase adds a phosphate group to form glycerol-3-phosphate.

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 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...

biosynthesis in bacteria

How Bacteria Build Key Macromolecules

Bacteria build essential macromolecules through tightly controlled biosynthetic pathways. These anabolic reactions make proteins, nucleic acids, lipids, and polysaccharides. The products support growth, cell division, and normal cell function. Bacterial biosynthesis starts with precursor metabolites from glycolysis, the pentose phosphate pathway, and the Krebs cycle. Important precursors include pyruvate, acetyl-CoA, and glucose-6-phosphate. Cells use these compounds to make the monomers that...

carbon-dioxide fixation

Microbial Carbon Fixation Pathways

Microbial carbon fixation pathways let prokaryotes turn carbon dioxide into organic molecules. This process supports biosynthesis, helps sustain ecosystems, and plays a role in the global carbon cycle. It also has industrial uses in carbon capture and bioproduct synthesis. Autotrophic organisms depend on this process to use CO2 as a carbon source in many environments. The Calvin cycle is the most common carbon fixation pathway. Cyanobacteria and other autotrophic prokaryotes use it, and it...

biosynthesis of polysaccharides

Activated Sugars for Polysaccharide Synthesis

Activated sugars drive polysaccharide synthesis in cells. Glycogen and starch are built from nucleoside diphosphate sugars, mainly uridine diphosphate glucose (UDPG) and adenosine diphosphate glucose (ADPG). These sugar donors act as high-energy intermediates in carbohydrate metabolism and biosynthesis. UDPG supports glycogen synthesis in animals and many bacteria. It forms when glucose-1-phosphate reacts with uridine triphosphate (UTP). UDP-glucose pyrophosphorylase catalyzes this reaction.

inorganic nitrogen assimilation

Nitrogen Uptake by Microbes

Nitrogen uptake by microbes is essential for making proteins, nucleic acids, and other cell parts. Many bacteria and archaea take in nitrogen as nitrate or ammonia. They then convert it into forms that can be built into biomolecules. When nitrate enters a cell, it goes through assimilatory nitrate reduction. This is a two-step process. First, nitrate reductase changes nitrate to nitrite using NADH or FAD as an electron donor, depending on environmental and cellular conditions. Then nitrite...

sulfur assimilation

Sulfur Uptake and Cysteine Synthesis

Sulfur uptake and cysteine synthesis are key parts of microbial metabolism. Sulfur is needed to build important biomolecules, including the amino acids cysteine and methionine, as well as cofactors such as coenzyme A and biotin. Microorganisms usually take in sulfur from the environment as sulfate, but sulfate must be changed before cells can use it. Because sulfate is highly oxidized, it must go through assimilatory sulfate reduction to become biologically useful. Some microorganisms can also...

amino acid biosynthetic pathways

Amino Acid Building from Cell Metabolites

Amino acid biosynthesis lets cells build amino acids from common metabolic intermediates. These amino acids support cell growth, protein synthesis, and metabolic regulation. The main source molecules come from glycolysis, the tricarboxylic acid (TCA) cycle, and the pentose phosphate pathway. Key precursors include alpha-ketoglutarate, pyruvate, oxaloacetate, phosphoenolpyruvate, and erythrose-4-phosphate. They supply the carbon skeletons needed to form amino acids. Nitrogen must also be added...

biosynthesis of nucleic acids

Nucleotide Building Blocks for DNA and RNA

Nucleotide biosynthesis makes the building blocks needed for DNA and RNA. Cells use this pathway to make purine and pyrimidine nucleotides and keep their supply balanced. That balance helps protect genetic integrity and supports normal cell function. Purine nucleotide synthesis starts with ribose-5-phosphate, a sugar made in the pentose phosphate pathway. PRPP synthetase adds phosphate groups to form phosphoribosyl pyrophosphate, or PRPP, which is the activated starting point for the pathway.

biosynthesis of lipids

How Membrane Lipids Vary Across Life

Membrane lipids vary across Bacteria, Archaea, and Eukarya, and these differences help cells survive in different environments. The three domains of life make lipids through distinct biosynthetic pathways. Those pathways create membranes with different stability, permeability, and flexibility. Bacteria and eukaryotes both build fatty acid-based lipids from acetyl-CoA and malonyl-CoA. The pathway includes condensation, reduction, and dehydration steps. Bacteria use a type II fatty acid...

formation of lipopolysaccharides

Lipopolysaccharides and Gram-Negative Defense

Lipopolysaccharides (LPS) are important parts of the outer membrane of Gram-negative bacteria. They help stabilize the membrane and help protect bacteria from host immune responses. LPS has three main parts: lipid A, a core oligosaccharide, and an O antigen. LPS biosynthesis and assembly depend on a coordinated set of enzymes and transport steps. The molecule is also known as an endotoxin. It can activate Toll-like receptor 4 (TLR4) in the host and trigger strong immune responses. In severe...

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

Description

Transcript

Tags