Recombinant Salmonella enteritidis PT4 UPF0114 protein YqhA (yqhA)

What are the optimal storage conditions for maintaining the stability of recombinant YqhA protein?

For optimal stability of recombinant YqhA protein, storage recommendations include:

• Short-term storage (up to one week): 4°C in working aliquots

• Standard storage: -20°C in Tris-based buffer containing 50% glycerol

• Long-term storage: -80°C in the same buffer formulation

Repeated freeze-thaw cycles should be avoided to maintain protein integrity. The protein is typically supplied in a storage buffer optimized specifically for its stability, consisting of a Tris-based buffer with 50% glycerol .

How does Salmonella enteritidis PT4 differ from other Salmonella strains in comparative genomic analyses?

Comparative genomic analysis reveals that Salmonella enteritidis PT4 (strain P125109) has several distinguishing features:

• It is classified as a host-promiscuous strain, unlike host-restricted strains such as S. Gallinarum.

• The genome shows extensive synteny with S. Typhimurium LT2, with >90% of coding sequences forming a core gene set with 98.98% average nucleotide identity between shared orthologs.

• S. Enteritidis PT4 possesses unique genomic regions of difference (RODs) compared to S. Typhimurium LT2, including prophage-like elements, fimbrial clusters, and metabolic islands.

• S. Enteritidis PT4 harbors 13 fimbrial clusters, with a novel cluster termed 'peg' that is restricted to S. Enteritidis, S. Gallinarum 287/91, and S. Paratyphi A .

What detection methods are commonly used for identifying Salmonella enteritidis PT4 in research settings?

Several detection methods are employed for identifying Salmonella enteritidis PT4:

Research demonstrates that while traditional methods like phage typing have been historically useful, whole genome sequencing offers superior discriminatory power for distinguishing between closely related isolates during outbreak investigations .

How can researchers differentiate between Salmonella enteritidis PT4 isolates in outbreak scenarios when traditional typing methods show identical profiles?

When traditional typing methods such as phage typing and MLVA show identical profiles for different isolates (as commonly seen with PT4 and MLVA profile 3-10-5-4-1), researchers should employ whole genome sequencing (WGS) for enhanced discrimination:

• WGS Analysis Protocol:

  • Sequence isolates on platforms like Illumina HiSeq

  • Analyze data using user-friendly tools such as CLC Genomics Workbench and resources from the Center for Genomic Epidemiology

  • Visualize genome comparisons with tools like BLAST Ring Image Generator (BRIG)

Case studies have demonstrated that WGS can successfully distinguish between simultaneous outbreaks of S. Enteritidis PT4 occurring in geographically separated locations when classical microbiological subtyping methods failed to provide sufficient discrimination. This approach also enables detection of additional genetic elements, such as plasmids carrying antibiotic resistance genes that may be present in variant phage types (e.g., PT4a) .

What is the evolutionary relationship between Salmonella enteritidis PT4 and other Salmonella serovars based on UPF0114 protein YqhA conservation?

The UPF0114 protein family, including YqhA, represents an interesting marker for evolutionary studies in Salmonella. Comparative analysis of the S. Enteritidis PT4 genome with S. Gallinarum 287/91 reveals that S. Gallinarum is likely a recently evolved descendant of S. Enteritidis.

While specific conservation data for YqhA across serovars is not directly provided in the search results, the broader genomic context shows:

• S. Enteritidis PT4 and S. Gallinarum 287/91 exhibit predominant similarity and synteny in core genome regions

• S. Gallinarum has undergone extensive genome degradation through deletion and pseudogene formation

• The average nucleotide identity between shared orthologs of S. Enteritidis PT4 and S. Typhimurium LT2 is 98.98%

Researchers investigating YqhA specifically should perform comparative protein sequence analysis across various Salmonella serovars to establish its conservation pattern and potential role in host adaptation or virulence.

What is the functional significance of UPF0114 protein YqhA in Salmonella enteritidis PT4 pathogenesis and host adaptation?

While the specific function of YqhA remains uncharacterized (hence the "UPF" designation for uncharacterized protein family), its potential role in pathogenesis can be inferred from several lines of evidence:

• Membrane association: The amino acid sequence suggests YqhA is likely a membrane-associated protein based on the presence of hydrophobic regions (WLLAPVYFGLSLALIALALKF) .

• Host adaptation context: S. Enteritidis PT4 is a host-promiscuous strain, and comparative genomic studies with host-restricted strains like S. Gallinarum provide insight into genetic determinants of host range. Pseudogene formation in host-adapted strains often affects membrane proteins and those involved in host-pathogen interactions .

• Genomic context: The gene (yqhA) is designated as SEN2996 in the S. Enteritidis PT4 genome . Examining neighboring genes and their regulation could provide clues to function.

Advanced research approaches to determine YqhA function include:

• Gene knockout studies to assess virulence in different animal models

• Protein localization assays to confirm membrane association

• Protein-protein interaction studies to identify binding partners

• Expression analysis under different infection-relevant conditions

How do epigenetic factors influence the expression of the yqhA gene in Salmonella enteritidis PT4 under different environmental conditions?

While the search results don't directly address epigenetic regulation of yqhA, researchers can investigate this question through the following methodological approaches:

• Environmental Condition Analysis:

  • Expose S. Enteritidis PT4 to conditions mimicking various environments:

    • Gastrointestinal tract (low pH, bile salts)

    • Intracellular (low Mg²⁺, antimicrobial peptides)

    • Food matrices (egg components, poultry environment)

    • Various temperatures (refrigeration, cooking, body temperature)

• Epigenetic Profiling Techniques:

  • Bisulfite sequencing to identify DNA methylation patterns

  • ChIP-seq to detect histone modifications near yqhA

  • ATAC-seq to assess chromatin accessibility

  • RNA-seq to quantify transcriptional changes

• Regulon Analysis:

  • Examine if yqhA is part of known Salmonella regulatory networks:

    • PhoPQ two-component system

    • RpoS stress response

    • HilA virulence regulator

This research direction is particularly relevant given that S. Enteritidis PT4 has been associated with numerous outbreaks, especially those linked to eggs and poultry products, suggesting adaptation to specific environmental niches .

What are the optimal conditions for expressing and purifying recombinant Salmonella enteritidis PT4 UPF0114 protein YqhA?

Based on available information about recombinant YqhA protein production, the following methodological approach is recommended:

Expression System Selection:

• Baculovirus expression systems have been successfully used for other Salmonella recombinant proteins

• E. coli-based systems using pET vectors are also suitable for bacterial proteins of similar size

Expression Protocol:

• Clone the full yqhA coding sequence (positions 1-164) into an appropriate expression vector

• Consider adding a purification tag (His-tag or GST-tag) - note that tag type may be determined during the production process

• Transform into expression host and induce protein expression (IPTG for E. coli systems)

• Harvest cells and lyse using appropriate buffer systems

Purification Strategy:

• Initial capture using affinity chromatography based on the chosen tag

• Secondary purification using ion exchange or size exclusion chromatography

• Final formulation in Tris-based buffer with 50% glycerol for stability

Quality Control:

• SDS-PAGE to verify size and purity

• Western blot for identity confirmation

• ELISA to confirm proper folding and epitope presentation

How can researchers design effective ELISA-based detection systems for Salmonella enteritidis PT4 using the UPF0114 protein YqhA as a target?

Developing an effective ELISA for detecting S. Enteritidis PT4 using YqhA protein involves the following methodological approach:

Antibody Development:

• Use purified recombinant YqhA protein to raise polyclonal antibodies in rabbits or develop monoclonal antibodies

• Screen antibodies for specificity against YqhA and lack of cross-reactivity with homologous proteins from other bacteria

ELISA Configuration Options:

• Direct ELISA: Immobilize sample on plate, detect with anti-YqhA antibody

• Sandwich ELISA: Capture antibody → sample → detection antibody

• Competitive ELISA: Sample competes with labeled YqhA for antibody binding

Optimization Parameters:

• Coating buffer composition and pH

• Blocking reagent selection

• Antibody concentrations and incubation times

• Wash buffer stringency

• Substrate selection for maximum sensitivity

Validation Protocol:

• Determine specificity against:

  • Other Salmonella serotypes

  • Non-Salmonella enterobacteria

  • Food matrix components

• Establish limit of detection (comparable to iQ-Check Salmonella II)

• Assess performance on artificially spiked samples:

  • Chicken carcass rinses

  • Turkey sponge swabs

  • Poultry boot swabs

  • Beef products

The XP-Design Assay for Salmonella Enteritidis has demonstrated 106% efficiency with an R² value of 0.9991, providing a benchmark for assay performance .

What genomic techniques should be employed to trace the evolutionary history of the yqhA gene in different Salmonella enteritidis phage types?

To trace the evolutionary history of the yqhA gene across different S. Enteritidis phage types, researchers should implement the following genomic analysis approach:

Sample Selection Strategy:

• Include diverse S. Enteritidis phage types (PT1, PT4, PT8, PT13a) from different geographical regions and time periods

• Include representatives from other Salmonella serovars for outgroup comparison

• Sample both outbreak and sporadic isolates to capture maximum diversity

Sequencing Methodologies:

• Whole Genome Sequencing (preferred approach)

  • Short-read sequencing (Illumina) for SNP detection

  • Long-read sequencing (PacBio/Nanopore) for structural variation

• Targeted amplicon sequencing of yqhA and flanking regions

Bioinformatic Analysis Pipeline:

• Sequence alignment of yqhA gene and protein sequences

• Phylogenetic analysis:

  • Maximum likelihood or Bayesian approaches

  • Selection pressure analysis (dN/dS ratios)

• Genomic context analysis:

  • Conservation of flanking genes

  • Mobile genetic element detection

• Population structure analysis:

  • PFGE patterns correlation with sequence types

  • Phage type association with genetic lineages

Epidemiological Context Integration:

• Correlate genetic findings with historical outbreak data

• Map geographical distribution of variants

• Assess temporal trends in gene evolution

This approach has proven valuable in previous studies of S. Enteritidis PT4, which identified geographical clustering of certain genetic variants and temporal shifts in predominant phage types .

What are the key considerations when designing mutation studies to determine the functional role of YqhA in Salmonella enteritidis PT4 virulence?

When designing mutation studies to investigate YqhA function in S. Enteritidis PT4 virulence, researchers should consider the following methodological framework:

Mutation Strategy Selection:

• Clean deletion (preferred):

  • Lambda Red recombinase system for precise gene removal

  • Include removal of antibiotic resistance marker when possible

• Point mutations:

  • Target conserved amino acids identified through sequence alignment

  • Consider membrane topology predictions when selecting targets

• Conditional expression:

  • Inducible/repressible promoter systems

  • Temperature-sensitive alleles

Phenotypic Characterization:

• In vitro assays:

  • Growth curves under various conditions

  • Stress resistance (acid, bile, oxidative)

  • Cell invasion assays (epithelial and macrophage cells)

  • Biofilm formation

  • Motility assessment

• In vivo infection models:

  • Mouse models (comparing S. Enteritidis-typical invasiveness)

  • Chicken models (egg contamination potential)

  • Consider comparative virulence with S. Gallinarum mutants

• Complementation studies:

  • Trans-complementation with wild-type yqhA

  • Complementation with homologs from other serovars

Molecular Mechanism Investigation:

• Transcriptomic analysis:

  • RNA-seq comparing wild-type vs. mutant

  • Identification of affected pathways

• Protein interaction studies:

  • Pull-down assays

  • Bacterial two-hybrid systems

• Structural studies:

  • Membrane localization confirmation

  • Potential transmembrane domain function

This approach follows the experimental model suggested for understanding host adaptation in S. enterica, where mutations in genes of host-promiscuous strains like S. Enteritidis PT4 are analyzed to understand the functional significance of pseudogenes present in host-adapted strains .

How should researchers interpret discrepancies between phage typing and molecular characterization of Salmonella enteritidis PT4 isolates expressing YqhA?

When faced with discrepancies between phage typing and molecular characterization results for S. Enteritidis PT4 isolates, researchers should apply the following analytical framework:

Hierarchical Evaluation Approach:

• Understand the limitations of phage typing:

  • Phage types can change in isolates (mentioned in source 7)

  • PT4 can have variants (e.g., PT4a) that still appear related by molecular methods

  • Some phage types predominate in specific geographical regions, limiting discriminatory power

• Resolution power comparison:

  Method	Discriminatory Power	Stability	Ease of Use
  Phage Typing	Moderate	May change	Requires reference laboratory
  PFGE	Higher	Stable	Standardized protocol
  MLVA	High	Stable	Rapid, standardized
  WGS	Highest	Most stable	Complex analysis

• Integration strategy:

  • Use hierarchical approach: start with phage typing for initial classification

  • Apply MLVA or PFGE for intermediate resolution

  • Resolve discrepancies with WGS for definitive characterization

  • Look for genetic elements that might explain phage type variation (e.g., plasmids or prophages)

A case example demonstrated that S. Enteritidis isolates identified as PT4 by phage typing (with one variant typed as PT4a) all had identical MLVA profiles (3-10-5-4-1), yet WGS analysis could clearly discriminate between separate outbreaks and identify an additional plasmid carrying antibiotic resistance in the PT4a variant .

What epidemiological insights can be gained from analyzing the distribution of YqhA sequence variants across global Salmonella enteritidis PT4 isolates?

Global Distribution Analysis:

• Geographical patterns:

  • PT4 was historically common in Europe before spreading globally

  • By 1999, PT4 represented 49% of S. Enteritidis outbreaks in the US, with 81% occurring in California

  • Regional clustering of specific genetic variants may indicate independent evolution or introduction events

• Temporal trends:

  • PT4 increased from 4% of US S. Enteritidis outbreaks in 1993 to 49% in 1999

  • Tracking YqhA sequence changes over this period could reveal adaptive mutations

• Source attribution:

  • Egg-associated outbreaks accounted for 80% of S. Enteritidis outbreaks with confirmed vehicles

  • Specific YqhA variants might correlate with particular food sources or environmental niches

Data Integration Methodology:

• Create a database linking:

  • YqhA sequence variants

  • Geographic origin

  • Isolation date

  • Source (human, food, animal)

  • Associated outbreak information

• Perform phylogeographic analysis to:

  • Track the global spread of specific variants

  • Identify convergent evolution in separate lineages

  • Correlate genetic changes with emergence in new regions

• Assess correlation with historical control measures:

  • Decline in S. Enteritidis infection rates from 3.9 per 100,000 in 1995 to 1.98 per 100,000 in 1999

  • Impact of on-farm testing, egg refrigeration regulations, and quality assurance programs

This approach aligns with the success seen in tracking S. Enteritidis PT4 outbreaks through combined molecular and epidemiological methods, and could reveal whether YqhA plays a role in the adaptation of PT4 to specific ecological niches or hosts .

What strategies can overcome challenges in expressing and purifying full-length membrane-associated YqhA protein from Salmonella enteritidis PT4?

Membrane-associated proteins like YqhA present unique challenges for recombinant expression and purification. Based on the protein's characteristics, researchers should consider the following troubleshooting strategies:

Expression System Optimization:

• E. coli strain selection:

  • Use C41(DE3) or C43(DE3) strains specifically developed for membrane protein expression

  • Consider BL21(DE3)pLysS to reduce basal expression toxicity

• Expression vector modifications:

  • Fusion tags: MBP, GST, or SUMO to enhance solubility

  • Twin-Strep or His8 tags for improved membrane protein purification

  • Codon optimization for E. coli expression

• Induction protocols:

  • Lower induction temperature (16-20°C)

  • Reduced IPTG concentration (0.1-0.5 mM)

  • Extended expression time (overnight)

Membrane Protein Extraction:

• Detergent screening panel:

  • Mild detergents: DDM, LMNG, or Digitonin

  • Zwitterionic detergents: LDAO, Fos-choline

  • Test multiple concentrations and combinations

• Solubilization optimization:

  • Buffer composition (pH 7.5-8.0 typically optimal)

  • Salt concentration (300-500 mM NaCl)

  • Glycerol addition (10-20%)

  • Solubilization time and temperature

Purification Refinement:

• Chromatography approach:

  • IMAC with extended washing steps

  • Size exclusion chromatography to remove aggregates

  • Consider amphipol exchange for improved stability

• Storage optimization:

  • Detergent concentration just above CMC

  • Addition of lipids or cholesterol hemisuccinate

  • Specialized storage at -20°C with 50% glycerol in Tris-based buffer

Quality Assessment:

• Circular dichroism to verify secondary structure

• Mass spectrometry to confirm correct mass

• Thermostability assays to optimize buffer conditions

These approaches have proven successful for membrane proteins similar to YqhA and follow best practices for handling proteins with transmembrane domains.

How can researchers address cross-reactivity issues when developing immunological detection methods for YqhA in complex sample matrices?

When developing immunological detection methods for YqhA in complex matrices like food samples or clinical specimens, researchers may encounter cross-reactivity challenges. The following strategic approach can help address these issues:

Antibody Optimization:

• Epitope mapping and selection:

  • Identify YqhA-specific epitopes with minimal homology to proteins from:

    • Other Salmonella serotypes

    • Related Enterobacteriaceae

    • Food matrix proteins

  • Target unique extracellular loops or termini

• Antibody production options:

  • Monoclonal antibodies for highest specificity

  • Recombinant antibody fragments (Fab, scFv)

  • Phage display selection under stringent conditions

• Affinity maturation:

  • Sequential panning against YqhA with negative selection steps

  • Competitive elution with specific YqhA peptides

Cross-reactivity Reduction:

• Sample pre-treatment:

  • Selective enrichment in specialized media

  • Centrifugation or filtration steps

  • Heat treatment to denature cross-reactive proteins

• Blocking optimization:

  • Milk proteins for food sample matrices

  • Serum albumin for clinical samples

  • Pre-adsorption of detection antibodies with related antigens

• Assay format modifications:

  • Sandwich ELISA with two different YqhA-specific epitopes

  • Competitive ELISA design

  • Multiplex detection with confirmatory markers

Validation Protocol:

• Cross-reactivity panel testing:

  • Test against library of Salmonella serotypes (>200 serotypes)

  • Include common food-borne pathogens

  • Test food matrices: chicken carcass rinses, turkey sponge swabs, poultry boot swabs, beef samples

• Statistical validation:

  • Determine specificity, sensitivity, PPV and NPV

  • Establish ROC curves for optimizing cut-off values

  • Compare performance to established methods like iQ-Check Salmonella II