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

La fotosintesi anossigena è un processo guidato dalla luce nei batteri di zolfo viola e verde che converte l'anidride carbonica e i donatori di elettroni alternativi, come l'idrogeno solforato, in composti organici senza produrre ossigeno. I fototrofi anossigenici operano con un unico fotosistema e si basano su pigmenti batterioclorofilliani situati nei cromatofori, nei clorosomi o nelle membrane citoplasmatiche. Nei batteri viola, il centro di reazione P870 eccita gli elettroni, trasferendoli attraverso la batteriofietina a un pool di chinoni, alle proteine del cluster ferro-zolfo e ai citocromi, restituendoli infine al centro di reazione. Questo processo di trasferimento di elettroni genera la forza motrice del protone per la sintesi dell'ATP. Inoltre, questi batteri utilizzano il flusso di elettroni inverso, alimentato dalla forza motrice del protone, per ridurre il NAD+ utilizzando donatori di elettroni esterni come l'idrogeno solforato o lo zolfo elementare. I batteri verdi dello zolfo, con P840 come centro di reazione, trasferiscono elettroni tramite batterioclorofille, proteine del cluster FeS, chinoni e citocromi. Questi batteri usano le ferredossine per ridurre direttamente il NAD+ a NADH, bypassando il flusso di elettroni inverso.

atp sintasi

Anoxygenic Photosynthesis

La fotosintesi anossigenica &#232; un processo fototrofico che cattura l&#8217;energia luminosa per guidare la fissazione del carbonio senza produrre ossigeno molecolare. A differenza della fotosintesi ossigenica, che utilizza l&#8217;acqua come donatore di elettroni e rilascia ossigeno, i fototrofi anossigenici usano donatori di elettroni alternativi come il solfuro di idrogeno (H_2S), lo zolfo elementare (S^0) o il tiosolfato (S_2O_3^2-). Questo processo &#232; realizzato da diversi gruppi di batteri, inclusi batteri porpora, batteri verdi dello zolfo, eliobatteri e altri fototrofi anossigenici, i quali hanno evoluto meccanismi fotosintetici specializzati basati su un singolo fotosistema.
Differenze tra fotosintesi ossigenica e anossigenica
La fotosintesi ossigenica e quella anossigenica differiscono principalmente per quanto riguarda i donatori di elettroni, la produzione di ossigeno e la composizione dei fotosistemi. La fotosintesi ossigenica, svolta da cianobatteri, alghe e piante, utilizza l&#8217;acqua (H_2O) come donatore di elettroni, generando ossigeno (O_2) come sottoprodotto. Essa impiega due fotosistemi (PSI e PSII) disposti secondo uno schema a Z, che consente la riduzione diretta di NADP^+ a NADPH. Al contrario, la fotosintesi anossigenica si basa su donatori alternativi come il solfuro di idrogeno o i composti organici e non rilascia ossigeno. Funziona attraverso un singolo fotosistema, impiegando principalmente il flusso ciclico degli elettroni per la sintesi di ATP, con alcuni batteri che richiedono il trasporto elettronico inverso per generare potere riducente. Inoltre, i fototrofi anossigenici utilizzano batterioclorofille al posto delle clorofille, permettendo loro di assorbire luce nell&#8217;infrarosso e prosperare in ambienti anaerobici o microaerofili.
Fotosistemi e trasporto degli elettroni
I fototrofi anossigenici si affidano a pigmenti di batterioclorofilla per assorbire l&#8217;energia luminosa. Questi pigmenti sono localizzati in strutture cellulari distinte: cromatofori nei batteri porpora, clorosomi nei batteri verdi dello zolfo e altre strutture specializzate associate alla membrana negli eliobatteri. L&#8217;energia assorbita da questi pigmenti eccita gli elettroni in centri di reazione specializzati&#8212;P870 nei batteri porpora non solforosi, P840 nei batteri verdi dello zolfo e varianti in altri fototrofi anossigenici.
Nei batteri porpora, gli elettroni eccitati dal centro di reazione P870 vengono trasferiti in sequenza tramite batteriofeofitina, una &#8220;pool&#8221; di chinoni, proteine con cluster ferro-zolfo (FeS) e citocromi, prima di tornare al centro di reazione. Questo flusso ciclico di elettroni genera un gradiente protonico attraverso la membrana, portando alla sintesi di ATP tramite chemiosmosi. Inoltre, i batteri porpora necessitano di un donatore di elettroni esterno, come il solfuro di idrogeno, per ridurre il NAD^+ a NADH. Tale riduzione avviene tramite trasporto elettronico inverso, che richiede un ulteriore apporto energetico fornito dalla forza proton-motrice.
I batteri verdi dello zolfo operano secondo un meccanismo di trasporto elettronico differente. Il centro di reazione P840 dona elettroni ad alta energia a una serie di accettori, tra cui batterioclorofille, proteine con cluster FeS, chinoni e citocromi. Tuttavia, a differenza dei batteri porpora, i batteri verdi dello zolfo utilizzano ferredoxine, che trasferiscono direttamente gli elettroni a NAD^+, formando NADH senza necessit&#224; di trasporto elettronico inverso. Questa efficienza consente ai batteri verdi dello zolfo di prosperare in ambienti a bassa intensit&#224; luminosa, come le sorgenti idrotermali profonde e i laghi stratificati.
Diversit&#224; dei fototrofi anossigenici
Oltre ai batteri porpora e ai batteri verdi dello zolfo, altri gruppi batterici eseguono la fotosintesi anossigenica. Gli eliobatteri, appartenenti al phylum Firmicutes, utilizzano un singolo fotosistema con batterioclorofilla g. A differenza degli altri fototrofi anossigenici, essi non possiedono estese membrane interne e realizzano la fotosintesi nella membrana citoplasmatica. I Chloroflexi, noti anche come batteri verdi non solforosi, impiegano una combinazione di metabolismo fototrofico ed eterotrofico, permettendo loro di sopravvivere in nicchie ecologiche diverse.
Significato ecologico ed evolutivo
La fotosintesi anossigenica &#232; fondamentale nei cicli biogeochimici globali, promuovendo le trasformazioni del carbonio e dello zolfo in ambienti anaerobici. Questi batteri contribuiscono alla produzione primaria in ecosistemi poveri di ossigeno e sono considerati come i precursori evolutivi dei fototrofi ossigenici moderni. La capacit&#224; di diversi gruppi batterici di utilizzare una variet&#224; di donatori di elettroni suggerisce che la vita fotosintetica primordiale sulla Terra potrebbe aver operato in condizioni anossigeniche prima dell&#8217;avvento della fotosintesi ossigenica con scissione dell&#8217;acqua. Inoltre, l&#8217;adattamento delle batterioclorofille all&#8217;assorbimento della luce infrarossa e a bassa intensit&#224; permette a questi batteri di prosperare in ambienti in cui i fototrofi ossigenici non sono competitivi, come acque profonde, sedimenti e sistemi idrotermali.

ATP Sintasi

La fotosintesi anossigenica &#232; un processo fototrofico che cattura l&#8217;energia luminosa per guidare la fissazione del carbonio senza produrre ...

Education

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Microbiology

Microbiologia

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Microbial Metabolism

Metabolismo microbico

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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

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

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