Recombinant Yersinia pestis Fumarate reductase subunit C (frdC)

How is frdC expression regulated during Y. pestis infection and environmental adaptation?

FrdC expression in Y. pestis is regulated by multiple environmental factors, with iron availability being a critical regulator. Proteomic analysis reveals that:

• Iron availability: Under iron-depleted conditions, fumarate reductase subunits including frdC show decreased abundance. This regulation is consistent with the presence of Fe-S clusters in the fumarate reductase complex and the need to conserve iron during limitation .

• Oxygen levels: Expression increases under anaerobic or microaerobic conditions, when fumarate respiration becomes more important for energy generation.

• Temperature: While some Y. pestis virulence factors show temperature-dependent regulation (26°C vs. 37°C), proteomic comparisons suggest little evidence for temperature-specific adaptation processes related to fumarate reductase in response to iron starvation .

Research has shown that this regulation is part of a broader metabolic shift in Y. pestis during iron starvation, where the bacterium transitions from iron-utilizing to iron-independent biochemical pathways in the cytoplasm .

What are the structural characteristics of Y. pestis frdC compared to other bacterial homologs?

Y. pestis frdC exhibits several structural features that are important for its function:

• Membrane-spanning domains: frdC contains multiple transmembrane helices that anchor the fumarate reductase complex to the cytoplasmic membrane.

• Heme binding sites: Similar to other bacterial fumarate reductase C subunits, Y. pestis frdC likely contains conserved histidine residues that serve as ligands for heme B groups. Specifically, the SdhC subunit (analogous to frdC) contains four conserved His residues which are known ligands for two heme B residues .

• Size and composition: The Y. pestis frdC protein is 130 amino acids in length with a molecular weight of approximately 15 kDa, classifying it as a "15 kDa hydrophobic protein" .

How does iron availability affect the expression and function of fumarate reductase in Y. pestis, and what are the methodological approaches to study this relationship?

Iron availability critically influences fumarate reductase expression and activity in Y. pestis through several mechanisms:

Research Findings:
Proteomic analysis of iron-starved Y. pestis KIM6+ cells revealed:

• Decreased abundance of fumarate reductase subunits containing Fe-S clusters

• Reduced activity of TCA cycle enzymes, including fumarate reductase

• A 2-fold to 2.8-fold higher aconitase activity (another Fe-S cluster enzyme) in lysates from iron-replete cells compared to iron-starved cells

Methodological Approaches:

• Differential Protein Expression Analysis:

  • Subcellular fractionation of Y. pestis grown under iron-replete and iron-depleted conditions

  • 2D gel electrophoresis coupled with mass spectrometry

  • Relative protein quantification using standardized spot intensities

• Enzyme Activity Assays:

  • Measure fumarate reductase activity spectrophotometrically by monitoring the oxidation of reduced benzyl viologen or NADH

  • Compare enzyme kinetics between lysates from iron-replete and iron-depleted cultures

  • Use specific inhibitors to confirm enzyme specificity

• Transcriptional Analysis:

  • RT-qPCR to measure frd operon transcript levels under varying iron concentrations

  • RNA-seq to identify co-regulated genes in the iron regulon

  • ChIP-seq to identify Fur (ferric uptake regulator) binding sites near the frd operon

To investigate the metabolic consequences of reduced fumarate reductase activity, researchers can employ metabolomics approaches to track changes in TCA cycle intermediates and identify alternative metabolic pathways activated during iron starvation, such as the observed upregulation of the pyruvate oxidase pathway in Y. pestis .

What are the optimal expression systems and purification protocols for producing functional recombinant Y. pestis frdC protein?

Producing functional recombinant Y. pestis frdC presents unique challenges due to its hydrophobic nature and membrane association. Based on current research practices, the following methodological approach is recommended:

Expression System Optimization:

• E. coli-based expression:

  • BL21(DE3) or C41(DE3) strains are preferred for membrane protein expression

  • Use pET-based vectors with an N-terminal His-tag for detection and purification

  • The full coding sequence (1-130 amino acids) should be included

• Expression conditions:

  • Lower induction temperatures (16-20°C) to reduce inclusion body formation

  • IPTG concentration: 0.1-0.5 mM

  • Extended expression time (overnight) at lower temperatures

Purification Protocol:

• Membrane fraction isolation:

  • Cell disruption by sonication or French press in Tris/PBS-based buffer (pH 8.0)

  • Differential centrifugation to isolate membrane fractions

  • Solubilization using detergents (n-dodecyl-β-D-maltoside or CHAPS at 1-2%)

• Affinity purification:

  • Nickel-NTA chromatography for His-tagged protein

  • Imidazole gradient elution (20-250 mM)

  • Buffer containing 0.05-0.1% detergent to maintain solubility

• Storage and handling:

  • Store in Tris/PBS-based buffer with 6% Trehalose at pH 8.0

  • Add 5-50% glycerol for long-term storage

  • Aliquot and store at -20°C/-80°C

  • Avoid repeated freeze-thaw cycles

Quality Control:

• Verify purity by SDS-PAGE (>90% purity should be achieved)

• Confirm identity by Western blot and/or mass spectrometry

• Assess functional activity if possible, though this may require reconstitution with other subunits

For reconstitution experiments, the protein should be briefly centrifuged prior to opening and reconstituted in deionized sterile water to a concentration of 0.1-1.0 mg/mL .

What is the relationship between Y. pestis fumarate reductase activity and bacterial virulence during infection?

The relationship between Y. pestis fumarate reductase and virulence is complex and involves metabolic adaptation during different phases of infection:

Metabolic Adaptation During Infection:

• Flea vector phase:

  • Y. pestis forms biofilms in the flea foregut that are essential for transmission

  • Biofilm formation is regulated by c-di-GMP levels controlled by diguanylate cyclases (DGCs) encoded by hmsT and y3730

  • Energy metabolism shifts during biofilm formation, potentially involving changes in fumarate reductase activity

• Mammalian host phase:

  • During transition from flea (26°C) to mammalian host (37°C), Y. pestis undergoes significant metabolic reprogramming

  • Under iron limitation in the host (part of nutritional immunity), decreased fumarate reductase activity likely triggers metabolic shifts:

    • Reduced TCA cycle activity

    • Increased reliance on alternative pathways, such as pyruvate oxidase (PoxB)

Research Findings:

• Iron acquisition systems (Ybt, Yfe, Yfu, Yiu, Hmu) increase in abundance during iron starvation, while metabolic enzymes dependent on Fe-S clusters (including fumarate reductase) decrease

• PoxB activity increases 5.3-7.8 fold in iron-starved cells, suggesting a metabolic shift to iron-independent pathways

Methodological Approaches to Study This Relationship:

• Genetic manipulation:

  • Construction of frdC deletion mutants

  • Complementation studies with wild-type and mutant frdC alleles

  • Conditional expression systems to regulate frdC expression during infection

• Animal infection models:

  • Mouse models of bubonic plague to assess virulence

  • Flea infection models to study transmission efficiency

  • In vivo imaging using bioluminescent Y. pestis strains to track infection progression

• Metabolic profiling:

  • Isotope labeling to track carbon flux through the TCA cycle versus alternative pathways

  • Comparative metabolomics of wild-type and frdC mutants during infection

While direct evidence linking fumarate reductase to Y. pestis virulence is limited, the metabolic flexibility provided by alternative respiratory pathways likely contributes to bacterial survival during different stages of infection, particularly under the iron-limited conditions encountered in mammalian hosts .

What inhibitors target Y. pestis fumarate reductase and how can they be developed as potential therapeutic agents?

Research on specific inhibitors of Y. pestis fumarate reductase is limited, but insights from related systems suggest several promising approaches for inhibitor development:

Known Inhibitors and Mechanisms:

• Quinone analog inhibitors:

  • 2,3-dimethyl-1,4-naphthoquinone (DMN) interacts with the quinone-binding site in the membrane anchor subunits (including frdC)

  • These compounds can disrupt electron transfer in the respiratory chain

• Natural product inhibitors:

  • Ferulenol and embelin have been identified as nanomolar inhibitors of MQO (malate:quinone oxidoreductase) in Campylobacter jejuni

  • These compounds may have cross-reactivity with fumarate reductase due to similar quinone-binding mechanisms

Methodological Approaches for Inhibitor Development:

• High-throughput screening (HTS):

  • Develop a continuous fluorescence-based assay for monitoring fumarate reductase activity

  • Screen compound libraries using the HTS assay

  • Validation with secondary biochemical assays

• Structure-based drug design:

  • Homology modeling of Y. pestis frdC based on solved structures from related organisms

  • Molecular docking to identify potential binding sites

  • Fragment-based screening to identify lead compounds

• Inhibitor evaluation protocol:

  • Determine IC50 values using enzyme kinetics assays

  • Assess antibacterial activity using growth inhibition assays

  • Determine the mode of inhibition (competitive, non-competitive, uncompetitive)

  • Evaluate selectivity against human enzymes

• In vivo testing methodology:

  • Mouse model of Y. pestis infection

  • Pharmacokinetic and pharmacodynamic studies

  • Combination studies with existing antibiotics

A promising approach is targeting the unique aspects of bacterial fumarate reductase that differ from mammalian succinate dehydrogenase, particularly the quinone binding sites in the membrane anchor subunits. For example, researchers have identified aryl stibonic acids that inhibit DNA adenine methyltransferase in Y. pestis with nanomolar potency (Ki = 6.46 nM for 4-stibonobenzenesulfonic acid) . Similar screening approaches could be applied to identify fumarate reductase inhibitors.

How do mutations in the frdC gene affect Y. pestis metabolism, respiratory chain function, and survival under different environmental conditions?

Mutations in the frdC gene can significantly impact Y. pestis metabolism and survival, particularly under anaerobic or microaerobic conditions where fumarate respiration becomes essential:

Potential Effects of frdC Mutations:

• Respiratory chain disruption:

  • Mutations in the conserved histidine residues that serve as heme ligands would disrupt electron transfer

  • Alterations in transmembrane domains could affect quinone binding and electron transfer efficiency

  • Changes in the interaction surfaces with other Frd subunits might destabilize the entire complex

• Metabolic consequences:

  • Impaired ability to utilize fumarate as a terminal electron acceptor

  • Reduced ATP generation under anaerobic conditions

  • Potential accumulation of reducing equivalents (NADH, FADH2)

  • Metabolic bottlenecks in the TCA cycle

Environmental Condition-Specific Effects:

Methodological Approaches to Study frdC Mutations:

• Site-directed mutagenesis:

  • Target conserved histidine residues in potential heme-binding sites

  • Modify predicted quinone-binding regions

  • Create chimeric proteins with frdC from other species

• Phenotypic characterization:

  • Growth curves under different oxygen tensions

  • Measurements of fumarate reduction rates

  • Membrane potential analysis using fluorescent probes

  • Respiration rates using oxygen electrodes

• Metabolomic analysis:

  • Measurement of TCA cycle intermediates

  • Redox cofactor (NAD+/NADH) ratios

  • Adenylate energy charge determination

  • Isotope labeling to track metabolic flux

• Proteomic analysis:

  • Assess compensatory changes in other respiratory enzymes

  • Monitor expression of alternative terminal reductases

  • Evaluate global metabolic reprogramming

Research on related systems suggests that fumarate reductase in bacteria that use menaquinone (such as Y. pestis) may operate via a reverse redox loop mechanism that depends on proton potential . Mutations disrupting this mechanism would have significant implications for energy conservation during anaerobic growth.

What are the optimal storage conditions and stability characteristics of recombinant Y. pestis frdC protein?

Ensuring stability of recombinant Y. pestis frdC protein is critical for experimental reproducibility. Based on available data, the following methodological guidelines should be followed:

Optimal Storage Conditions:

• Short-term storage (up to one week):

  • Store working aliquots at 4°C

  • Maintain in Tris/PBS-based buffer with 6% Trehalose at pH 8.0

• Long-term storage:

  • Store at -20°C/-80°C

  • Add glycerol to a final concentration of 5-50% (optimal: 50%)

  • Prepare small aliquots to avoid repeated freeze-thaw cycles

• Lyophilization:

  • For maximum stability, the protein can be stored as lyophilized powder

  • Ensure complete desiccation and store with desiccant

  • Protect from humidity during storage

Reconstitution Protocol:

• Briefly centrifuge the vial prior to opening to bring contents to the bottom

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

• If needed for long-term storage, add glycerol to 5-50% final concentration and prepare aliquots

Stability Characteristics:

Quality Control Methods:

• Functional assessment: If activity assays are available, periodically test activity under standardized conditions

• Physical stability: Monitor for precipitation or aggregation

• SDS-PAGE analysis: Confirm integrity and absence of degradation products

• Western blot: Verify the presence of intact epitopes if antibodies are available

Repeated freeze-thaw cycles should be strictly avoided as they significantly reduce protein stability and activity. For critical experiments, always use fresh aliquots of the protein .

What experimental approaches can be used to study the interaction between frdC and other subunits of the fumarate reductase complex?

Investigating the interactions between frdC and other fumarate reductase subunits requires specialized techniques for membrane protein complexes. The following methodological approaches are recommended:

Protein-Protein Interaction Analysis:

• Co-immunoprecipitation (Co-IP):

  • Express tagged versions of different Frd subunits

  • Use antibodies against the tags to pull down protein complexes

  • Identify interacting partners by Western blot or mass spectrometry

  • Challenge: requires solubilization in detergents that maintain interactions

• Bacterial two-hybrid systems:

  • Adapted for membrane proteins (BACTH system)

  • Fuse frdC and potential interaction partners to complementary fragments of adenylate cyclase

  • Measure interaction through cAMP-dependent reporter gene activation

• Crosslinking studies:

  • Use membrane-permeable crosslinkers with different spacer lengths

  • Apply to intact cells or membrane preparations

  • Identify crosslinked products by mass spectrometry

  • Map interaction interfaces at amino acid resolution

Structural Analysis Methods:

• Cryo-electron microscopy:

  • Purify intact fumarate reductase complex in detergent micelles or nanodiscs

  • Determine structure at near-atomic resolution

  • Map the interaction interfaces between subunits

• X-ray crystallography:

  • Challenging for membrane proteins but possible with advanced crystallization techniques

  • Lipidic cubic phase crystallization

  • Use of antibody fragments to stabilize the complex

• NMR spectroscopy:

  • Solution NMR for solubilized proteins or fragments

  • Solid-state NMR for membrane-embedded complexes

  • Measure chemical shift perturbations upon complex formation

Functional Interaction Studies:

• Reconstitution experiments:

  • Express and purify individual subunits

  • Reconstitute in liposomes or nanodiscs in different combinations

  • Measure enzymatic activity to determine essential interactions

• Mutagenesis approach:

  • Introduce mutations at predicted interaction interfaces

  • Assess impact on complex assembly and stability

  • Measure enzymatic activity of mutant complexes

• Electron transfer measurements:

  • Use rapid kinetic techniques to measure electron transfer rates

  • Compare wild-type and mutant complexes

  • Correlate structural features with electron transfer efficiency

The membrane-embedded nature of frdC makes these interactions particularly challenging to study. Careful optimization of detergent conditions is critical, as different detergents may preferentially stabilize different protein-protein interactions within the complex.

How can researchers differentiate between the functions of fumarate reductase and succinate dehydrogenase in Y. pestis metabolism studies?

Distinguishing between fumarate reductase (Frd) and succinate dehydrogenase (Sdh) activities in Y. pestis is challenging due to their similar catalytic functions and the ability of these enzymes to catalyze the same reaction in opposite directions. The following methodological approaches can help researchers differentiate between these activities:

Biochemical Differentiation Methods:

• Enzyme kinetics analysis:

  • Fumarate reductase: Higher affinity for fumarate and menaquinol

  • Succinate dehydrogenase: Higher affinity for succinate and ubiquinone

  • Measure enzyme activities in both directions under standardized conditions

  • Compare Km and Vmax values to determine predominant activity

• Electron donor/acceptor specificity:

  • Test activity with different quinones (menaquinone vs. ubiquinone)

  • Fumarate reductase typically couples better with menaquinol

  • Succinate dehydrogenase typically couples better with ubiquinone

• pH dependence of activity:

  • Measure activity across a pH range (pH 6-8)

  • The optimal pH may differ between the forward and reverse reactions

Genetic and Molecular Approaches:

• Gene deletion studies:

  • Create specific deletions in frd and sdh operons

  • Characterize growth phenotypes under aerobic vs. anaerobic conditions

  • Measure specific enzyme activities in deletion strains

• Expression analysis:

  • Monitor transcript levels of frd and sdh genes under different conditions

  • Use RT-qPCR or RNA-seq to quantify expression

  • Correlate expression with measured enzyme activities

• Protein identification:

  • Use mass spectrometry to identify which enzyme complex is present

  • Distinguish between FrdC and SdhC peptides

  • Quantify relative abundance under different growth conditions

Experimental Design Considerations:

Specialized Assay Protocols:

• Direction-specific activity measurements:

  • Fumarate reduction: Monitor oxidation of reduced benzyl viologen at 578 nm

  • Succinate oxidation: Monitor reduction of artificial electron acceptors like dichlorophenolindophenol (DCPIP)

• Proton potential dependency:

  • Measure activity in the presence/absence of protonophores (CCCP)

  • Succinate dehydrogenase from menaquinone-containing bacteria typically requires a proton potential for activity

• Membrane potential measurements:

  • Use fluorescent dyes (DiSC3) to monitor membrane potential

  • Correlate enzyme activity with changes in membrane potential

Research has shown that succinate dehydrogenases from menaquinone-containing bacteria (like Y. pestis) often use a reverse redox loop mechanism and require a proton potential to drive endergonic succinate oxidation . This characteristic can be exploited to differentiate between Sdh and Frd activities.

What are the latest methodological advances in detecting and quantifying Y. pestis in environmental and clinical samples using frdC as a target?

While frdC itself is not commonly used as a primary target for Y. pestis detection, understanding the methodological approaches for bacterial detection is valuable for researchers working with this pathogen. Here are current methodological advances that could be applied to frdC-based detection:

Nucleic Acid-Based Detection Methods:

• Real-time PCR targeting frdC:

  • Design specific primers for the Y. pestis frdC gene

  • Develop probe-based assays for increased specificity

  • Quantification range: 10²-10⁸ copies/reaction

  • Potential sensitivity: 10³-10⁴ CFU/mL in clinical samples

• LAMP (Loop-mediated isothermal amplification):

  • Isothermal amplification at 60-65°C

  • Rapid detection (30-60 minutes)

  • Visual detection possible (turbidity or colorimetric)

  • Field-deployable without sophisticated equipment

• Digital PCR:

  • Absolute quantification without standard curves

  • Higher tolerance to inhibitors than conventional PCR

  • Improved detection of low-abundance targets

  • Useful for environmental samples with PCR inhibitors

Protein-Based Detection Methods:

• Lateral Flow Assay (LFA):

  • Could be developed with anti-frdC antibodies

  • Detection limit of approximately 10⁵ CFU/mL (based on F1 antigen detection)

  • Results available in less than 10 minutes

  • Simple to use in field settings

• ELISA-based detection:

  • Sandwich ELISA using anti-frdC antibodies

  • Quantitative results with standard curves

  • Typical detection limits: 10⁴-10⁵ CFU/mL

  • Available as commercial kits for specific antigens

Emerging Technologies:

• CRISPR-Cas-based detection:

  • High specificity targeting frdC sequence

  • Cas12/Cas13-based detection systems (SHERLOCK, DETECTR)

  • Attomolar sensitivity possible

  • Multiplexed detection in single reaction

• Biosensors:

  • Electrochemical detection using frdC-specific aptamers

  • Surface plasmon resonance (SPR) with specific antibodies

  • Quartz crystal microbalance (QCM) sensors

  • Potentially rapid (minutes) and sensitive (10³-10⁴ CFU/mL)

Comparison of Detection Methods:

For specific detection of Y. pestis, researchers have developed lateral flow assays using the F1 antigen that can detect 10⁵ CFU/mL in less than 10 minutes with no cross-reactivity to other Yersinia species . Similar approaches could be developed targeting frdC if specific antibodies are available.

How does the structure and function of Y. pestis frdC compare with homologous proteins in other bacterial pathogens?

The structure and function of Y. pestis frdC can be compared with homologous proteins in other bacterial pathogens to understand evolutionary relationships and functional adaptations:

Structural Comparisons:

• Transmembrane organization:

  • Y. pestis frdC contains transmembrane helices similar to other bacterial homologs

  • The protein is 130 amino acids in length, consistent with frdC subunits in other Enterobacteriaceae

  • Contains conserved histidine residues that likely serve as heme B ligands, similar to other bacterial species

• Heme binding sites:

  • Most bacterial frdC proteins contain two heme B molecules

  • These hemes are typically coordinated by four conserved histidine residues

  • In some bacteria like Bacillus subtilis, SdhC (analogous to frdC) uses a reverse redox loop mechanism dependent on these hemes

• Quinone binding sites:

  • Species-specific adaptations for interaction with different quinone types

  • Y. pestis likely uses menaquinone as electron carrier, similar to other Gram-negative bacteria under anaerobic conditions

Functional Comparisons:

Evolutionary Significance:

• Operon organization:

  • Y. pestis and sulphate-reducing bacteria like Desulfovibrio contain frdCAB or sdhCAB gene clusters

  • These lack a distinct frdD or sdhD gene, which is present in some other bacteria

  • This suggests evolutionary divergence in the membrane anchor components

• Functional adaptation:

  • In menaquinone-containing bacteria, succinate dehydrogenase requires a proton potential to drive endergonic succinate oxidation

  • This adaptation is reflected in the structure of SdhC (similar to FrdC)

  • The SdhC subunit in these bacteria lacks a Glu residue in transmembrane helix IV, which is part of the uncoupling E-pathway in non-electrogenic FrdABC enzymes

Understanding these structural and functional relationships can provide insights into metabolic adaptations of Y. pestis to its unique lifestyle, transitioning between an arthropod vector and mammalian host with different metabolic requirements.

How do posttranslational modifications affect the structure and function of Y. pestis frdC, and how can these be studied experimentally?

Posttranslational modifications (PTMs) of Y. pestis frdC remain largely unexplored but could significantly impact its structure, function, and regulation. Here are methodological approaches to investigate these modifications:

Potential Posttranslational Modifications:

• Heme incorporation:

  • Critical for electron transfer function

  • May be affected by iron availability

  • Could be regulated during different growth phases

• Phosphorylation:

  • Potential regulation mechanism for activity

  • Might respond to environmental signals

  • Could affect interaction with other subunits

• Oxidative modifications:

  • Cysteine oxidation during oxidative stress

  • Potential impact on protein stability and function

  • May be relevant during host immune response

Methodological Approaches:

• Mass Spectrometry-Based PTM Identification:

  • Sample preparation protocol:

    • Purify recombinant or native frdC under non-denaturing conditions

    • Enzymatic digestion (trypsin, chymotrypsin, or combination)

    • Enrichment of modified peptides if necessary

  • Analysis techniques:

    • LC-MS/MS with high-resolution instruments

    • Electron transfer dissociation (ETD) for labile modifications

    • Multiple reaction monitoring (MRM) for targeted analysis

    • Data analysis with PTM-specific search algorithms

• Site-Directed Mutagenesis to Confirm PTM Sites:

  • Replace potentially modified residues with non-modifiable analogs

  • Compare activity and stability of wild-type and mutant proteins

  • Assess impacts on protein-protein interactions

• PTM-Specific Antibodies:

  • Generate antibodies against specific modifications

  • Use for Western blotting and immunoprecipitation

  • Assess presence of modifications under different conditions

• Heme Incorporation Studies:

  • UV-visible spectroscopy to monitor heme binding

  • Resonance Raman spectroscopy for heme coordination state

  • Comparison of holo- and apo-protein properties

• Kinetic Analysis of Modified Protein:

  • Compare enzyme kinetics before and after specific modifications

  • Assess impact on substrate binding and catalysis

  • Determine if modifications alter quinone specificity

Experimental Design for PTM Studies:

For membrane proteins like frdC, special considerations must be made when studying PTMs, including careful selection of detergents that preserve modifications, enrichment strategies for low-abundance membrane proteins, and targeted MS approaches to detect substoichiometric modifications that may be functionally significant.

What role does Y. pestis frdC play in biofilm formation and how does this compare to other respiratory enzymes?

The relationship between Y. pestis frdC and biofilm formation represents an intriguing area of research that connects respiratory metabolism with virulence. While direct evidence specifically linking frdC to biofilm formation is limited, several lines of evidence suggest potential connections:

Metabolic Basis for Biofilm Formation:

• Energy metabolism in biofilms:

  • Biofilms create microenvironments with oxygen gradients

  • Cells deep in biofilms experience anaerobic/microaerobic conditions

  • Alternative respiratory pathways including fumarate reduction become important

  • frdC as part of fumarate reductase may support energy generation in these niches

• Biofilm regulation in Y. pestis:

  • Biofilm formation is critical for transmission from fleas to mammals

  • Regulated by intracellular levels of c-di-GMP

  • Controlled by two diguanylate cyclases (HmsT and Y3730) and one phosphodiesterase (HmsP)

  • Environmental niche strongly influences the relative contribution of these enzymes

Experimental Evidence and Comparative Analysis:

• Differential regulation:

  • Similar to the differential control of biofilm formation in vitro vs. in the flea vector by HmsT and Y3730 , frdC expression might be differentially regulated

  • Iron availability affects frdC expression and may also influence biofilm formation

• Comparative analysis with other respiratory enzymes:

  • Pyruvate oxidase B (PoxB) increases in abundance under iron starvation while fumarate reductase decreases

  • This shift may reflect adaptation to different environmental niches including biofilms

Methodological Approaches to Study frdC in Biofilm Formation:

• Genetic manipulation studies:

  • Construction of frdC deletion mutants

  • Analysis of biofilm formation in vitro (crystal violet assays)

  • Examination of biofilm formation in flea vectors

  • Complementation studies to confirm phenotypes

• Spatiotemporal expression analysis:

  • Reporter constructs (frdC promoter fused to GFP/luciferase)

  • Visualization of expression in different regions of biofilms

  • Correlation with oxygen gradients using microelectrodes

• Metabolic analysis of biofilms:

  • Metabolomic profiling of wild-type vs. frdC mutant biofilms

  • Isotope labeling to track carbon flux through TCA cycle

  • Measurement of redox balance in different biofilm regions

• Comparative transcriptomics:

  • RNA-seq analysis of planktonic vs. biofilm cells

  • Comparison of frdC expression with other respiratory enzymes

  • Identification of co-regulated genes

Research Model for Testing:

While Y. pestis biofilm formation in the flea vector is primarily studied in the context of the Hms system and c-di-GMP signaling , the metabolic adaptations required for growth in biofilms likely involve shifts in respiratory metabolism, potentially including increased reliance on fumarate reductase activity.