Recombinant Sulfurimonas denitrificans ATP synthase subunit c (atpE)

What is the basic structure and function of ATP synthase subunit c in Sulfurimonas denitrificans?

ATP synthase subunit c (atpE) in Sulfurimonas denitrificans is a 104 amino acid protein that forms part of the F₀ sector of the F₀F₁-ATP synthase complex. The protein functions as a critical component of the c-ring structure that rotates during ATP synthesis. The full amino acid sequence is: MKKILFLMVALATAALANDGDVANQTLKAYSMIAAGLGLGLAALGGAIGMGHTAAATIAG TARNPGLGAKLMTTMFIALAMIEAQVIYALVIALIALYANPYLG .

This c-subunit, like in other organisms, participates in proton translocation through the F₀ domain, which drives the rotation of the c-ring relative to the a-subunit. This mechanical motion is ultimately coupled to ATP synthesis in the F₁ domain of the complex. The protein contains hydrophobic regions that anchor it in the membrane, with specific residues that participate in proton binding and release during the rotary catalysis mechanism .

How does the atpE gene in Sulfurimonas denitrificans compare to other prokaryotic ATP synthase c-subunits?

The atpE gene in Sulfurimonas denitrificans encodes a protein that shares structural similarities with other prokaryotic ATP synthase c-subunits while maintaining species-specific adaptations. Comparative analysis shows that like other bacterial c-subunits, it contains a conserved carboxylate residue (typically glutamate or aspartate) crucial for proton binding and translocation.

The c-subunit of S. denitrificans is notably similar in function to those found in other chemolithoautotrophic bacteria, but exhibits sequence variations that may reflect adaptations to the organism's specific environmental niche. Unlike some other ATP synthases where mutations in a single c-subunit moderately affect function, studies on other bacterial ATP synthases (like Bacillus PS3) have shown that multiple mutations in the c-ring can have compounding effects on ATP synthesis and proton pumping activities .

What are the optimal storage conditions for recombinant Sulfurimonas denitrificans ATP synthase subunit c?

For optimal storage of recombinant S. denitrificans ATP synthase subunit c, follow these methodological guidelines based on experimental evidence:

• Store lyophilized powder at -20°C/-80°C upon receipt

• After reconstitution, prepare working aliquots to avoid repeated freeze-thaw cycles

• Reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL

• Add glycerol to a final concentration of 50% for long-term storage

• Store working aliquots at 4°C for up to one week only

These guidelines ensure protein stability and prevent activity loss due to degradation. Research has shown that repeated freeze-thaw cycles significantly diminish protein functionality by disrupting secondary and tertiary structures. The addition of glycerol acts as a cryoprotectant by preventing ice crystal formation that can damage protein structure.

How does the c-subunit cooperate with other subunits in the ATP synthase complex during proton translocation and ATP synthesis?

The c-subunit of ATP synthase functions within a complex cooperative mechanism that enables energy conversion. Recent research indicates that the oligomeric c-ring demonstrates functional cooperation among individual c-subunits that impacts the efficiency of the entire complex. Studies on similar ATP synthases have shown that key glutamic acid residues in different c-subunits contribute to both proton release to and uptake from the a-subunit during rotation .

This cooperative mechanism involves:

• Sequential protonation/deprotonation of conserved carboxylate residues

• Coordinated conformational changes that enable rotation

• Interaction with the a-subunit at the a/c interface to form the proton translocation pathway

• Transmission of torque to the central stalk of the F₁ sector

Research on Bacillus PS3 ATP synthase has demonstrated that introducing mutations (such as E56D) in multiple c-subunits has a more pronounced negative effect on activity than single mutations. Notably, the effect is magnified when mutations are spatially separated within the c-ring, providing strong evidence for long-range cooperation among c-subunits .

For experimental investigation of this cooperation in S. denitrificans, researchers should consider creating genetically fused single-chain c-rings with various combinations of wild-type and mutant subunits, similar to approaches used with other bacterial ATP synthases.

What are the structural differences between ATP synthase subunit c (atpE) and subunit a (atpB) in Sulfurimonas denitrificans, and how do these differences relate to their functions?

ATP synthase subunits c (atpE) and a (atpB) in Sulfurimonas denitrificans exhibit significant structural and functional differences despite their cooperative roles in the F₀ sector:

Functionally, subunit c forms a rotary ring that carries protons across the membrane as it turns, while subunit a provides the stationary half-channel that allows protons to access the c-ring from opposite sides of the membrane. The a-subunit (atpB) contains essential arginine residues that participate in the proton release mechanism, interacting with the conserved carboxylate residues on the c-subunits .

This structural complementarity is essential for the proton motive force to drive rotation of the c-ring relative to the a-subunit, ultimately powering ATP synthesis in the F₁ sector of the complex.

What experimental approaches can determine the oligomeric state of the c-ring in Sulfurimonas denitrificans ATP synthase?

Determining the oligomeric state of the c-ring in S. denitrificans ATP synthase requires multiple complementary approaches:

• X-ray Crystallography:

  • Purify the c-ring using affinity chromatography with His-tagged constructs

  • Conduct crystallization trials in detergent-lipid mixed micelles

  • Analyze diffraction patterns to resolve the number of c-subunits per ring

  • Compare with similar bacterial ATP synthases that typically contain 8-15 c-subunits

• Cryo-Electron Microscopy (Cryo-EM):

  • Prepare purified ATP synthase complexes on EM grids

  • Collect and process images to generate 3D reconstructions

  • Count the number of c-subunits from the symmetry of the c-ring

  • Validate results against biochemical data

• Mass Spectrometry Approaches:

  • Perform native mass spectrometry on purified c-rings

  • Calculate the oligomeric state from the observed molecular weight

  • Cross-validate using chemical cross-linking followed by SDS-PAGE analysis

• Genetic Fusion Strategy:

  • Create genetically fused single-chain c-rings with defined numbers of subunits

  • Test the functionality of these constructs in complementation assays

  • Determine the native stoichiometry by comparing activity profiles

The c-ring stoichiometry is particularly important as it determines the H⁺/ATP ratio, which affects the bioenergetic efficiency of the enzyme. Researchers should note that c-ring size varies across species as an adaptation to different environmental conditions and energy requirements.

How can I design experiments to assess the effect of site-directed mutations in the atpE gene on ATP synthase activity?

To systematically assess the effects of site-directed mutations in the S. denitrificans atpE gene, implement the following experimental design:

• Mutation Selection Strategy:

  • Target conserved residues identified through multiple sequence alignment

  • Focus on the conserved carboxylate residue essential for proton binding

  • Design conservative (e.g., E→D) and non-conservative (e.g., E→A) mutations

  • Create mutations at both the proton-binding site and peripheral regions

• Expression System Setup:

  • Clone the wild-type and mutant atpE genes into an E. coli expression vector

  • Include an N-terminal His-tag for purification purposes

  • Express in E. coli as demonstrated for other recombinant S. denitrificans proteins

  • Optimize expression conditions (temperature, induction time, IPTG concentration)

• Functional Assays:

  • ATP Synthesis Activity: Measure ATP production using luciferase-based assays

  • ATP Hydrolysis Activity: Quantify Pi release using malachite green or enzyme-coupled assays

  • Proton Pumping: Assess using pH-sensitive fluorescent dyes in reconstituted proteoliposomes

  • Binding Studies: Examine proton or inhibitor binding using isothermal titration calorimetry

• Advanced Approaches:

  • Create a single-chain c-ring with multiple copies of atpE (wild-type or mutant)

  • Test combinations of mutations at different positions within the c-ring

  • Assess positional effects by varying the distance between mutations

  • Investigate potential cooperative effects among c-subunits

This comprehensive approach will provide insights into the structure-function relationship of the c-subunit and its role in the ATP synthase complex. Comparing results with similar studies on other bacterial ATP synthases will contextualize findings within the broader understanding of ATP synthase mechanisms.

What purification strategy would yield the highest purity of recombinant Sulfurimonas denitrificans ATP synthase subunit c for structural studies?

For high-purity recombinant S. denitrificans ATP synthase subunit c suitable for structural studies, implement this optimized purification protocol:

• Expression Optimization:

  • Express the His-tagged protein in E. coli BL21(DE3) or C43(DE3) (specialized for membrane proteins)

  • Culture at lower temperatures (16-20°C) after induction to enhance proper folding

  • Use auto-induction media to achieve higher cell density and protein yields

• Extraction and Solubilization:

  • Harvest cells and disrupt by sonication or high-pressure homogenization

  • Isolate membrane fraction by ultracentrifugation

  • Solubilize membrane proteins using mild detergents such as n-dodecyl-β-D-maltoside (DDM) or lauryl maltose neopentyl glycol (LMNG)

• Multi-step Purification Strategy:

  • Step 1: Immobilized metal affinity chromatography (IMAC) using Ni-NTA

    • Apply solubilized protein to Ni-NTA column equilibrated with buffer containing detergent

    • Wash extensively to remove non-specifically bound proteins

    • Elute with imidazole gradient (50-300 mM)

  • Step 2: Size exclusion chromatography (SEC)

    • Further purify using Superdex 200 column

    • Analyze fractions using SDS-PAGE and Western blotting

  • Step 3: Ion exchange chromatography (optional)

    • Apply pooled SEC fractions to resource Q or S column

    • Elute with salt gradient

• Quality Control Assessments:

  • Verify purity by SDS-PAGE (>95% purity required for structural studies)

  • Confirm identity by mass spectrometry and N-terminal sequencing

  • Assess protein homogeneity using dynamic light scattering

  • Evaluate secondary structure using circular dichroism spectroscopy

• Buffer Optimization for Structural Studies:

  • Screen various detergents and buffer conditions using thermal shift assays

  • For crystallization, concentrate to 5-10 mg/mL in optimal buffer

  • For cryo-EM, prepare in appropriate grid conditions

This protocol incorporates recent advances in membrane protein purification techniques to achieve the high purity required for structural studies while maintaining the native conformation of the protein .

How can I reconstitute purified Sulfurimonas denitrificans ATP synthase subunit c into liposomes for functional studies?

For functional reconstitution of purified S. denitrificans ATP synthase subunit c into liposomes, follow this detailed methodological approach:

• Liposome Preparation:

  • Prepare lipid mixture (recommended: 75% phosphatidylcholine, 20% phosphatidylethanolamine, 5% cardiolipin)

  • Dissolve lipids in chloroform, evaporate under nitrogen gas to form a thin film

  • Hydrate lipid film with reconstitution buffer (e.g., 20 mM HEPES, 100 mM KCl, pH 7.4)

  • Perform freeze-thaw cycles (5-10 times) followed by extrusion through polycarbonate filters (400 nm, then 200 nm)

• Protein-Liposome Integration:

  • Method A: Detergent-mediated reconstitution

    • Solubilize preformed liposomes with detergent (DDM at a concentration just above CMC)

    • Add purified protein at lipid-to-protein ratio of 50:1 to 100:1 (w/w)

    • Remove detergent by dialysis or adsorption to Bio-Beads SM-2

  • Method B: Direct incorporation during liposome formation

    • Add purified protein directly to the detergent-solubilized lipids

    • Form proteoliposomes by detergent removal

• Verification of Reconstitution:

  • Confirm protein incorporation using freeze-fracture electron microscopy

  • Assess protein orientation by limited proteolysis

  • Determine reconstitution efficiency using protein assays before and after reconstitution

• Functional Assays for Reconstituted Systems:

  • Proton Translocation Assay:

    • Load proteoliposomes with pH-sensitive fluorescent dye (ACMA or pyranine)

    • Measure fluorescence changes upon establishment of pH gradient

  • ATP Synthesis/Hydrolysis:

    • For complete ATP synthase, impose pmf by acid-base transition or K⁺/valinomycin

    • Measure ATP production using luciferase-based assays

  • Patch-Clamp Electrophysiology:

    • Form giant unilamellar vesicles (GUVs) containing the reconstituted protein

    • Perform patch-clamp to measure single-channel conductance

• Control Experiments:

  • Use protein-free liposomes as negative controls

  • Incorporate known ATP synthase inhibitors to validate specific activity

  • Compare with reconstituted wild-type ATP synthase complex as positive control

This methodological framework enables rigorous investigation of the functional properties of S. denitrificans ATP synthase subunit c in a controlled membrane environment, closely resembling its native conditions.

What bioinformatic approaches can identify key functional residues in Sulfurimonas denitrificans ATP synthase subunit c?

To identify key functional residues in S. denitrificans ATP synthase subunit c (atpE), implement these comprehensive bioinformatic approaches:

• Sequence Conservation Analysis:

  • Perform multiple sequence alignment (MSA) using CLUSTAL W, MUSCLE, or T-Coffee

  • Include c-subunits from diverse bacterial species, particularly other epsilon-proteobacteria

  • Calculate conservation scores using ConSurf or similar tools

  • Identify highly conserved residues, particularly focusing on carboxylate residues (Glu/Asp)

• Structural Prediction and Analysis:

  • Generate homology models using SWISS-MODEL, Phyre2, or AlphaFold

  • Use known crystal structures of c-subunits (e.g., from E. coli or Bacillus PS3) as templates

  • Identify residues located at interfaces with other subunits, particularly the a-subunit

  • Map conserved residues onto the structural model to visualize functional sites

• Molecular Dynamics Simulations:

  • Embed the predicted structure in a lipid bilayer using CHARMM-GUI

  • Perform equilibrium MD simulations to identify stable conformations

  • Analyze proton coordination sites and conformational flexibility

  • Simulate protonation/deprotonation events to model functional cycle

• Evolutionary Analysis:

  • Construct phylogenetic trees of c-subunits across species

  • Perform evolutionary trace analysis to identify class-specific residues

  • Use coevolution analysis to identify residue networks functionally linked

• Integrated Functional Prediction:

  • Combine conservation, structural, and evolutionary data to score each residue

  • Compare with known functional residues in well-studied ATP synthases

  • Prioritize residues for experimental validation

Example of predicted key functional residues:

*Hypothetical positions based on typical c-subunit structures; actual positions would be determined through analysis of the S. denitrificans sequence.

These methodological approaches provide a robust framework for predicting key functional residues, which can then be targeted for site-directed mutagenesis experiments to validate their roles.

How can I interpret the differences in ATP synthase activity between wild-type and mutant forms of Sulfurimonas denitrificans ATP synthase subunit c?

When interpreting differences in ATP synthase activity between wild-type and mutant forms of S. denitrificans ATP synthase subunit c, apply this systematic analytical framework:

• Quantitative Activity Assessment:

  • Compare absolute activity values (μmol ATP/min/mg protein)

  • Calculate relative activity (% of wild-type)

  • Determine kinetic parameters (Km, Vmax) for ATP synthesis/hydrolysis

  • Analyze proton translocation rates and H⁺/ATP ratios

• Statistical Analysis Approach:

  • Perform experiments with at least three biological replicates

  • Apply appropriate statistical tests (t-test, ANOVA with post-hoc analysis)

  • Calculate p-values and establish significance thresholds

  • Present data with error bars representing standard deviation or standard error

• Structure-Function Correlation:

  • Map mutations onto structural models

  • Correlate activity changes with specific structural features

  • Analyze potential disruptions to protein-protein interfaces

  • Consider effects on proton-binding residues vs. structural residues

• Cooperative Effects Analysis:

  • For c-ring with multiple mutations, analyze position-dependent effects

  • Compare single vs. double mutations to identify cooperative or additive effects

  • Assess whether mutations at different positions show distance-dependent effects

  • Create a heat map of activity based on mutation position combinations

• Integrated Data Interpretation Framework:

• Control Considerations:

  • Verify protein expression levels are comparable between wild-type and mutants

  • Confirm proper membrane insertion and complex assembly

  • Rule out secondary effects on protein stability

  • Account for potential compensatory mechanisms

This methodological framework allows researchers to systematically interpret differences between wild-type and mutant forms, distinguishing between direct effects on catalytic function and indirect effects on structure or assembly. Studies on other bacterial F₀F₁-ATP synthases have shown that positional effects of mutations in the c-ring can reveal important insights about the cooperative mechanism of proton translocation .

What does differential expression of ATP synthase genes in Sulfurimonas denitrificans reveal about its metabolic adaptations?

Differential expression of ATP synthase genes in Sulfurimonas denitrificans provides significant insights into the organism's metabolic adaptations to various environmental conditions. A methodological approach to interpreting this data includes:

• Transcriptomic Analysis Framework:

  • Compare expression levels of atpE (c-subunit) and other ATP synthase genes under different growth conditions

  • Analyze co-expression patterns with other metabolic genes

  • Identify regulatory elements in promoter regions of ATP synthase genes

  • Correlate expression changes with environmental parameters (O₂, pH, nitrate, sulfur compounds)

• Metabolic Context Integration:

  • Analyze expression patterns in relation to S. denitrificans' chemolithoautotrophic lifestyle

  • Connect ATP synthase expression to nitrate-dependent oxidation pathways

  • Examine correlation with genes involved in U(IV) and Fe(II) oxidation

  • Map expression changes onto metabolic network models

• Comparative Expression Analysis:

  • Compare S. denitrificans expression patterns with other Epsilonproteobacteria

  • Identify unique expression signatures related to its ecological niche

  • Contrast with expression patterns in heterotrophic bacteria

• Functional Correlation Table:

• Evolutionary Adaptation Insights:

  • Identify gene duplication or specialized isoforms of ATP synthase components

  • Analyze selection pressure on ATP synthase genes

  • Compare c-subunit sequence with organisms from similar and different ecological niches

  • Evaluate potential horizontal gene transfer events

S. denitrificans, as a chemolithoautotrophic bacterium capable of anaerobic, nitrate-dependent U(IV) and Fe(II) oxidation , likely shows specific ATP synthase expression patterns reflecting its unique energy conservation strategies. The ATP synthase complex plays a crucial role in capturing the energy generated from these electron transfer pathways, and expression changes would reflect adaptation to different electron donors and acceptors available in its environment.

How can I use Sulfurimonas denitrificans ATP synthase subunit c as a model system to study proton-coupled energy transduction?

Sulfurimonas denitrificans ATP synthase subunit c offers a valuable model system for studying proton-coupled energy transduction, particularly in chemolithoautotrophic organisms. Here's a methodological framework for utilizing this system:

• Experimental System Establishment:

  • Develop an expression system for S. denitrificans atpE gene product

  • Create chimeric ATP synthases with c-subunits from S. denitrificans in a well-characterized bacterial background

  • Establish reconstituted systems with purified components

  • Generate single-chain c-rings with defined composition

• Proton Transport Mechanism Studies:

  • Identify key proton-binding residues through site-directed mutagenesis

  • Measure proton binding affinity and pKa values using pH-dependent spectroscopic methods

  • Characterize proton translocation pathways using molecular dynamics simulations

  • Correlate proton binding/release with conformational changes

• Bioenergetic Analysis Approaches:

  • Determine H⁺/ATP ratio through simultaneous measurement of proton flux and ATP synthesis

  • Quantify thermodynamic efficiency under various conditions

  • Analyze operation near equilibrium vs. far from equilibrium

  • Measure threshold potential required for ATP synthesis

• Comparative Framework with Other Systems:

  • Compare with ATP synthases from organisms with different metabolic strategies

  • Analyze adaptations specific to chemolithoautotrophic lifestyle

  • Evaluate differences from heterotrophic bacterial systems

• Advanced Biophysical Techniques Application:

  • Single-molecule FRET to monitor conformational changes during catalysis

  • Solid-state NMR to characterize protonation states of key residues

  • High-speed AFM to visualize c-ring rotation

  • Cryo-EM to resolve structural states during the catalytic cycle

The c-subunit from S. denitrificans is particularly valuable as a model system because it functions in an organism with a unique bioenergetic profile, capable of generating proton motive force through anaerobic, nitrate-dependent U(IV) and Fe(II) oxidation . Studies on Bacillus PS3 ATP synthase have already demonstrated the importance of cooperative interactions among c-subunits , and similar approaches can be applied to understand the potentially unique adaptations in S. denitrificans ATP synthase.

What insights can structural studies of Sulfurimonas denitrificans ATP synthase subunit c provide for the design of synthetic molecular motors?

Structural studies of S. denitrificans ATP synthase subunit c can provide significant insights for designing synthetic molecular motors based on biomimetic principles:

• Key Structural Features to Analyze:

  • Determine the precise arrangement of transmembrane helices

  • Characterize the proton-binding pocket architecture

  • Analyze the oligomeric assembly principles of the c-ring

  • Identify structural elements that facilitate rotation

• Energy Transduction Mechanism Extraction:

  • Map the pathway of how protonation events trigger conformational changes

  • Quantify the energy profile along the rotation pathway

  • Identify molecular ratchet mechanisms that ensure unidirectional motion

  • Analyze how thermal fluctuations are harnessed for directional movement

• Design Principles for Synthetic Motors:

• Comparative Structural Analysis:

  • Contrast with ATP synthases from extremophiles

  • Identify unique adaptations in S. denitrificans

  • Compare with other rotary molecular machines (bacterial flagellum, etc.)

  • Analyze convergent and divergent design principles

• Implementation Strategies for Synthetic Systems:

  • Develop simplified peptide-based rotary motors inspired by c-subunit structure

  • Design hybrid systems incorporating key structural elements from ATP synthase

  • Create modular components based on functional domains

  • Establish minimal models that retain core functionality

The c-subunit's ability to convert the chemical energy of a proton gradient into mechanical rotary motion represents one of nature's most efficient molecular machines. Studies on other bacterial ATP synthases have shown that cooperative interactions among c-subunits are critical for function , and understanding these principles in S. denitrificans can inform the design of synthetic systems that harness similar cooperative mechanisms for efficient energy conversion at the nanoscale.

What are the most significant open questions regarding Sulfurimonas denitrificans ATP synthase subunit c that require further research?

Despite advances in understanding ATP synthase structure and function, several significant questions regarding S. denitrificans ATP synthase subunit c remain unresolved:

• Structural Specializations:

  • What is the exact stoichiometry of the c-ring in S. denitrificans ATP synthase?

  • Are there unique structural adaptations that reflect the organism's chemolithoautotrophic lifestyle?

  • How does the structure differ from ATP synthases in organisms with different metabolic strategies?

• Functional Mechanisms:

  • What is the precise mechanism of proton translocation through the Fo sector?

  • How do the c-subunits cooperate with each other and with the a-subunit during rotation?

  • Are there unique regulatory mechanisms controlling ATP synthase activity in response to varying environmental conditions?

• Evolutionary Considerations:

  • How has the c-subunit evolved to optimize function in the S. denitrificans ecological niche?

  • Are there signatures of adaptation to specific environmental conditions?

  • What evolutionary constraints have shaped the conservation of key functional residues?

• Integration with Metabolism:

  • How is ATP synthase activity coordinated with electron transport systems during nitrate-dependent Fe(II) and U(IV) oxidation?

  • What regulatory networks control ATP synthase expression and assembly?

  • How does ATP synthase contribute to the organism's ability to thrive in its ecological niche?

• Technical Challenges:

  • Can we develop improved expression and purification systems for structural studies?

  • What are the best approaches for functional reconstitution of the complete ATP synthase complex?

  • How can advanced biophysical techniques be applied to study the dynamics of the c-ring during catalysis?

Addressing these questions will require interdisciplinary approaches combining structural biology, biochemistry, biophysics, and systems biology. Comparative studies with other bacterial ATP synthases, particularly those from the Bacillus PS3 system where cooperative c-subunit interactions have been demonstrated , will be especially valuable in contextualizing findings from S. denitrificans.

How does understanding Sulfurimonas denitrificans ATP synthase contribute to our broader knowledge of bioenergetics in chemolithoautotrophic bacteria?

Understanding S. denitrificans ATP synthase contributes significantly to our broader knowledge of bioenergetics in chemolithoautotrophic bacteria through several key perspectives:

• Energy Conservation in Unique Metabolic Pathways:
  S. denitrificans can perform anaerobic, nitrate-dependent U(IV) and Fe(II) oxidation , which represents a specialized form of energy metabolism. The ATP synthase must be adapted to harness the proton motive force generated by these unique electron transport chains, providing insights into how chemolithoautotrophs optimize energy capture from inorganic substrates.

• Adaptation to Environmental Constraints:
  As a chemolithoautotroph, S. denitrificans must maximize energy efficiency when growing on inorganic electron donors. Understanding its ATP synthase reveals adaptive strategies for energy conservation under conditions where energy sources are limiting or variable.

• Evolutionary Perspective on Bioenergitics:
  Comparative analysis of ATP synthase components across different metabolic types of bacteria illuminates evolutionary pathways of bioenergetic systems and how they have been tailored to diverse ecological niches and metabolic strategies.

• Integration of Carbon and Energy Metabolism:
  In chemolithoautotrophs, energy generation must be tightly coupled to carbon fixation. The study of S. denitrificans ATP synthase provides insights into how these organisms balance ATP production with the high energy demands of autotrophic carbon fixation.

• Ecological and Biogeochemical Significance:
  Understanding the bioenergetics of S. denitrificans has broader implications for biogeochemical cycling, as this organism participates in sulfur, nitrogen, iron, and uranium transformations in the environment . The ATP synthase is the final component in capturing energy from these transformations.