Recombinant Erwinia tasmaniensis p-hydroxybenzoic acid efflux pump subunit AaeA (aaeA)

What is Erwinia tasmaniensis AaeA and what is its role in bacterial physiology?

Erwinia tasmaniensis AaeA is a membrane protein subunit of the p-hydroxybenzoic acid efflux pump system. It functions as part of a multidrug efflux mechanism that exports potentially toxic compounds from bacterial cells. E. tasmaniensis is a non-phytopathogenic bacterium that was first isolated from flowers and bark of apple and pear trees in Australia (Victoria, Tasmania, and Queensland) . This efflux pump plays a critical role in bacterial defense against antimicrobial compounds, contributing to the organism's survival mechanisms in its natural environment.

The full-length AaeA protein consists of 310 amino acids and exhibits characteristics of membrane proteins with transmembrane domains . The protein's primary function involves the export of p-hydroxybenzoic acid and potentially other aromatic compounds that could be toxic to the bacterial cell if allowed to accumulate intracellularly. Unlike many Erwinia species, E. tasmaniensis is not pathogenic to plants, suggesting that its efflux systems may have adapted primarily for environmental survival rather than virulence .

How do researchers differentiate between Erwinia tasmaniensis efflux systems and those of pathogenic Erwinia species?

Researchers employ multiple comparative approaches to differentiate between efflux systems. Phylogenetic analysis using 16S rRNA gene sequencing reveals that E. tasmaniensis is closely related to pathogenic Erwinia species like E. amylovora, but maintains distinct genetic characteristics that correspond to its non-pathogenic nature . When examining efflux systems specifically, researchers use phenotypic assays to determine substrate specificity differences between species.

Methodologically, researchers perform substrate utilization tests, as E. tasmaniensis differs from other Erwinia species in that it utilizes rhamnose but not citrate, and reduces nitrates into nitrites . These metabolic differences correlate with genomic adaptations, including those in efflux pump systems. Direct comparison studies using heterologous expression in model organisms like E. coli with deleted native efflux systems (such as ΔacrAB) allow for functional characterization of the transported substrates and efflux efficiency .

When comparing AaeA to efflux pump components from pathogenic species, researchers typically employ:

• Genome-wide analyses to identify homologous genes

• Comparative protein structure prediction

• Substrate specificity assays using radiolabeled or fluorescent compounds

• Antibiotic susceptibility testing in wild-type versus efflux pump mutants

• Heterologous expression studies to assess function in controlled genetic backgrounds

What experimental approaches are most effective for characterizing substrate specificity of the E. tasmaniensis AaeA efflux pump?

Characterizing substrate specificity of bacterial efflux pumps requires a multi-faceted experimental approach. For E. tasmaniensis AaeA, researchers employ several complementary methods:

Heterologous Expression Systems:
The most effective approach involves expressing E. tasmaniensis AaeA in E. coli strains with deleted native efflux pumps (e.g., ΔacrAB strains) . This creates a clean genetic background for functional characterization. The methodology typically involves:

• Cloning aaeA into an expression vector with an inducible promoter

• Transforming into E. coli efflux-deficient strains

• Comparing substrate export between transformants and controls

Substrate Accumulation Assays:
Researchers employ fluorescent dyes like Hoechst 33342 or ethidium bromide that fluoresce strongly when bound to intracellular components. The methodology includes:

• Loading bacterial cells with fluorescent dyes

• Monitoring fluorescence decrease as dyes are exported

• Comparing efflux rates in the presence/absence of potential substrates (competitive inhibition)

• Quantifying differences using spectrofluorimetry

MIC Determination:
Minimum inhibitory concentration (MIC) testing against various antibiotics and toxic compounds provides indirect evidence of substrate specificity:

• Testing growth inhibition against a panel of antibiotics from different classes

• Comparing wild-type, knockout mutants, and complemented strains

• Including efflux pump inhibitors (EPIs) like thioridazine, chlorpromazine, and fluoxetine to confirm pump involvement

Direct Transport Assays:
For definitive characterization, researchers utilize:

• Radiolabeled substrates to track transport across membranes

• Liposome reconstitution with purified AaeA protein to study transport in a defined system

• Measurement of substrate concentration gradients across membranes

Studies comparing AaeA with other RND efflux systems like those found in A. baumannii (AdeABC and AdeIJK) provide valuable comparative data regarding substrate profiles and efflux efficiencies .

How can recombinant E. tasmaniensis AaeA be optimally expressed and purified for structural studies?

Optimal expression and purification of membrane proteins like AaeA presents significant challenges. Based on available literature, the following methodological approach is recommended:

Expression System Selection:

• E. coli BL21(DE3) is commonly used for overexpression of recombinant AaeA with an N-terminal His-tag

• Alternative expression hosts include specialized E. coli strains (C41, C43) designed for membrane protein expression

• Yeast systems (Pichia pastoris) may provide better folding for complex membrane proteins

Expression Optimization:

• Use low induction temperatures (16-20°C) to minimize inclusion body formation

• Employ slow induction using lower IPTG concentrations (0.1-0.5 mM)

• Consider auto-induction media for gentler expression kinetics

• Add glycerol (5-10%) to stabilize membrane proteins during expression

Purification Protocol:

• Cell lysis using pressure disruption in buffer containing protease inhibitors

• Membrane fraction isolation through differential centrifugation

• Solubilization using mild detergents (DDM, LDAO, or C12E8)

• IMAC purification using Ni-NTA resin with imidazole gradient elution

• Size-exclusion chromatography for final purification and buffer exchange

Critical Buffer Components:

• Include 10-15% glycerol throughout purification to maintain stability

• Use Tris-based buffers (pH 7.5-8.0) with 100-300 mM NaCl

• Maintain detergent above critical micelle concentration

• Include reducing agents (1-5 mM DTT or 2-10 mM β-mercaptoethanol)

Based on commercial protocols for similar proteins, the following storage conditions are recommended: store at -20°C/-80°C as aliquots in Tris/PBS-based buffer containing 50% glycerol at pH 8.0 . For reconstitution, use deionized sterile water to achieve a concentration of 0.1-1.0 mg/mL.

What evidence exists for the role of AaeA in antimicrobial resistance in Erwinia species compared to pathogenic bacteria?

Current evidence suggests nuanced differences in the role of efflux pumps like AaeA between non-pathogenic Erwinia species and pathogenic bacteria:

Substrate Specificity Differences:
Evidence suggests that the substrate profile of AaeA in E. tasmaniensis may be narrower than those of pathogenic counterparts:

• Primary function appears oriented toward exporting plant-derived antimicrobial compounds like p-hydroxybenzoic acid

• May confer lower levels of resistance to clinical antibiotics compared to efflux systems in pathogenic species

• Likely evolved for survival in plant environments rather than for clinical antibiotic evasion

Quantitative Resistance Comparison:
When similar expression levels are achieved in heterologous systems, studies of RND pumps show quantifiable differences in efficacy:

• AdeABC from A. baumannii is less effective than E. coli AcrAB-TolC for lipophilic β-lactams, novobiocin, and ethidium bromide, but more effective for tetracycline efflux

• While specific data for E. tasmaniensis AaeA is limited, its evolutionary history as a non-pathogenic organism suggests it may have distinct substrate preferences

Genetic Regulation Differences:
Pathogenic organisms often have complex regulatory systems for efflux pump expression:

• Overexpression of efflux pumps in clinical isolates is frequently linked to mutations in regulatory genes

• Non-pathogenic Erwinia species likely maintain tighter regulation of efflux systems, expressing them only when required for environmental detoxification

The research indicates that while structural similarities exist between efflux systems in pathogenic and non-pathogenic bacteria, their functional roles and regulatory mechanisms have diverged through evolution, with environmental bacteria like E. tasmaniensis likely using these systems primarily for ecological fitness rather than clinical antibiotic resistance .

How can molecular modeling and comparative genomics enhance our understanding of AaeA function?

Molecular modeling and comparative genomics provide powerful approaches to understand AaeA function without requiring difficult experimental procedures for membrane proteins:

Homology Modeling Methodology:

• Identify structural homologs using HHpred or SWISS-MODEL

• Use resolved structures of related RND pump components as templates

• Employ molecular dynamics simulations to refine models in membrane environments

• Identify potential substrate binding pockets and conformational changes

Comparative Genomics Approaches:
The availability of multiple Erwinia genomes enables effective comparative analyses:

• Examine synteny of aaeA gene clusters across Erwinia species to identify associated components

• Compare with well-characterized systems like AcrAB-TolC from E. coli

• Identify conserved sequence motifs that may indicate functional significance

• Study prophage distribution in Erwinia genomes, as some efflux systems may be horizontally acquired

Integrated Analysis Framework:
A comprehensive understanding requires integration of multiple approaches:

Recent genomic analyses reveal that prophages are abundant elements integrated into Erwinia genomes and contribute to inter-strain genetic variability . This suggests horizontal gene transfer may play a role in the evolution and distribution of efflux systems across species, potentially including genes encoding AaeA-like proteins.

What techniques are most effective for studying AaeA interactions with other efflux pump components?

Understanding multicomponent membrane complexes like efflux pumps requires specialized approaches to characterize protein-protein interactions:

Co-Immunoprecipitation Studies:

• Express AaeA with an epitope tag (His, FLAG, etc.)

• Use tag-specific antibodies to pull down AaeA and associated proteins

• Identify interacting partners using mass spectrometry

• Verify interactions using reciprocal pull-downs with tagged partner proteins

Bacterial Two-Hybrid Systems:
This approach is particularly valuable for membrane proteins:

• Fuse AaeA and potential partners to split reporter proteins (adenylate cyclase domains)

• Co-expression in a reporter strain yields signal only if proteins interact

• Screen multiple constructs with truncated domains to map interaction interfaces

Fluorescence-Based Approaches:

• FRET (Förster Resonance Energy Transfer) using fluorescently-tagged proteins

• BiFC (Bimolecular Fluorescence Complementation) where fluorescent protein fragments reconstitute when fusion proteins interact

• Confocal microscopy to visualize co-localization in bacterial cells

Cross-Linking Mass Spectrometry:
For detailed structural information:

• Treat intact cells or purified complexes with chemical cross-linkers

• Digest cross-linked samples and analyze by MS/MS

• Identify cross-linked peptides to map interaction interfaces at amino acid resolution

Functional Complementation Studies:
A key approach using genetic methods:

• Construct strains with individual efflux components deleted

• Express wild-type or mutated versions on plasmids

• Assess restoration of efflux activity using substrate accumulation assays

• Use chimeric proteins to map functional domains

Studies of RND efflux systems in A. baumannii and E. coli provide methodological frameworks . In these systems, the RND transporter (analogous to AaeA's role) interacts with periplasmic adapter proteins and outer membrane factors to form a complete tripartite pump. Similar approaches can be applied to study E. tasmaniensis AaeA interactions with its partner proteins.

What are the recommended protocols for assessing inhibition of AaeA-mediated efflux?

Developing reliable assays for efflux inhibition is critical for studying AaeA function and potential applications in antimicrobial discovery:

Fluorescent Dye Accumulation Assay:
The most widely used method involves fluorescent substrates:

• Pretreat bacterial cells expressing AaeA with potential inhibitors at sub-MIC concentrations

• Add fluorescent substrates like ethidium bromide, Hoechst 33342, or Nile Red

• Monitor fluorescence increase as dye accumulates when efflux is inhibited

• Quantify using microplate reader with appropriate excitation/emission settings

• Calculate IC50 values for inhibitor potency comparison

Real-Time Efflux Assays:
For kinetic measurements:

• Load cells with fluorescent substrates at low temperature to allow accumulation

• Rapidly add glucose and raise temperature to energize cells

• Monitor fluorescence decrease as substrate is exported

• Compare efflux rates with/without inhibitors

• Analyze initial rates to determine inhibition mechanism (competitive vs. non-competitive)

Growth Inhibition Potentiation:
To assess physiological relevance:

• Determine MICs of antibiotics known to be AaeA substrates

• Repeat MIC determination in presence of sub-inhibitory concentrations of efflux inhibitors

• Calculate fold-change in antibiotic potency (potentiation factor)

• Compare results between wild-type and AaeA-deleted strains

Research with halophilic archaea has demonstrated that efflux pump inhibitors (EPIs) like thioridazine, chlorpromazine, and fluoxetine can be used at sub-MIC concentrations (½ MIC or ¼ MIC) to assess efflux inhibition . These compounds may serve as positive controls for developing novel inhibitors targeting AaeA.

How can transcriptional regulation of aaeA be effectively studied in different environmental conditions?

Understanding transcriptional regulation of efflux pumps provides insights into their physiological roles and potential drug targets:

Reporter Gene Fusion Approach:

• Clone the aaeA promoter region upstream of a reporter gene (lacZ, gfp, lux)

• Transform into E. tasmaniensis or heterologous hosts

• Expose to various environmental conditions (plant extracts, antibiotics, pH changes)

• Quantify reporter activity to determine promoter response

• Use deletion analysis to map regulatory elements within the promoter

RT-qPCR Analysis:
For direct measurement of native transcript levels:

• Grow bacteria under various conditions

• Extract total RNA using hot phenol or commercial kits with DNase treatment

• Synthesize cDNA using reverse transcriptase

• Perform qPCR with aaeA-specific primers

• Normalize to reference genes (rpoD, gyrA) using the ΔΔCt method

Transcription Factor Identification:
To identify regulatory proteins:

• Perform DNA-affinity chromatography using the aaeA promoter region

• Analyze bound proteins by mass spectrometry

• Confirm interactions using electrophoretic mobility shift assays (EMSA)

• Construct knockout mutants of putative regulators to verify their role

Whole-Transcriptome Analysis:
For comprehensive regulatory networks:

• Perform RNA-Seq on bacteria grown under various conditions

• Identify co-regulated genes that form regulatory networks with aaeA

• Use comparative transcriptomics between wild-type and regulatory mutants

• Apply bioinformatic approaches to identify regulatory motifs

The study of auxotrophic mutants in E. amylovora demonstrated that bacterial physiology and gene expression change significantly in response to host metabolites . Similar approaches can be applied to study how plant-derived compounds regulate aaeA expression in E. tasmaniensis, potentially revealing how this non-pathogenic bacterium has adapted to its ecological niche.

What are the challenges and solutions in functional reconstitution of AaeA in artificial membrane systems?

Reconstitution of membrane proteins in artificial systems presents unique challenges but offers powerful approaches for mechanistic studies:

Challenges in AaeA Reconstitution:

Methodological Approach for Reconstitution:

• Purify AaeA using mild detergents (DDM, LDAO) with glycerol for stability

• Prepare liposomes with E. coli total lipid extract or defined mixtures (POPC/POPE/POPG)

• Mix protein and liposomes at appropriate ratios (1:50 to 1:200 protein:lipid)

• Remove detergent using one of several methods:

  • Dialysis (gentle but slow)

  • Bio-Beads SM-2 adsorption (faster but potentially harsh)

  • Cyclodextrin complexation (controlled rate)

• Verify reconstitution by:

  • Freeze-fracture electron microscopy

  • Dynamic light scattering

  • Proteoliposome flotation on sucrose gradients

Transport Assay Development:
For functional verification:

• Encapsulate fluorescent substrates in proteoliposomes during reconstitution

• Establish ion gradients to energize transport (pH, Na+, K+)

• Monitor fluorescence changes over time using stopped-flow techniques

• Compare with control liposomes lacking protein

Research on MATE efflux pumps from halophilic archaea has demonstrated that functional reconstitution of these systems is feasible, allowing detailed mechanistic studies . Similar approaches can be applied to E. tasmaniensis AaeA, potentially revealing insights into its transport mechanism and substrate specificity.

How might comparative studies between E. tasmaniensis AaeA and homologous proteins in pathogenic bacteria inform novel antimicrobial strategies?

Comparative research between non-pathogenic and pathogenic bacterial efflux systems offers valuable insights for antimicrobial development:

Structural Divergence Analysis:

• Identify structural differences between AaeA and pathogenic homologs that could be exploited for selective targeting

• Focus on substrate binding pockets and conformational mechanisms

• Use site-directed mutagenesis to confirm the role of divergent residues

• Develop homology models to guide rational inhibitor design

Evolutionary Pressure Assessment:

• Analyze selection pressures on efflux pump genes across bacterial lineages

• Identify highly conserved regions critical for function versus variable regions

• Target conserved regions for broad-spectrum inhibitors

• Exploit variable regions for species-selective compounds

Transport Mechanism Comparison:
Studies of RND efflux systems in A. baumannii (AdeABC and AdeIJK) have shown quantifiable differences in substrate specificity compared to E. coli AcrAB-TolC . Similar comparative analyses between E. tasmaniensis AaeA and pathogenic counterparts might reveal:

• Different energy coupling mechanisms

• Altered substrate recognition determinants

• Unique regulatory control points

• Variable interactions with partner proteins

Inhibitor Development Strategy:
Based on comparative findings:

• Screen for compounds that selectively inhibit pathogenic efflux pumps

• Design competitive inhibitors that exploit structural differences

• Develop molecules that disrupt assembly of multicomponent pumps

• Target regulatory pathways unique to pathogenic species

The non-pathogenic nature of E. tasmaniensis provides a valuable "control" system to understand how efflux pumps in pathogenic bacteria have evolved specialized functions related to virulence and antibiotic resistance . This comparative approach could lead to antimicrobial strategies that selectively target pathogenic species while sparing beneficial or commensal bacteria.

What role does AaeA play in bacterial adaptation to plant environments versus pathogenic interactions?

The ecological context of E. tasmaniensis as a non-pathogenic plant-associated bacterium raises important questions about AaeA's role in adaptation:

Ecological Function Analysis:
E. tasmaniensis was isolated from flowers and bark of apple and pear trees but is non-pathogenic, unlike many other Erwinia species . This suggests AaeA may contribute to:

• Tolerance of plant-derived antimicrobial compounds

• Adaptation to fluctuating nutrient availability in plant surfaces

• Survival during plant defense responses

• Competition with other microbial colonizers

Comparative Expression Studies:
Research approaches might include:

• Transcriptomic comparison of E. tasmaniensis versus pathogenic Erwinia species when exposed to plant extracts

• Analysis of aaeA expression in different plant microenvironments (flowers, leaves, bark)

• Monitoring expression during plant colonization versus pathogenic invasion

• Comparison of regulation in response to plant defense compounds

Substrate Relevance to Plant Environment:
The preference for p-hydroxybenzoic acid suggests specialization:

• This compound is a common plant phenolic found in cell walls

• It has antimicrobial properties that may inhibit bacterial growth

• AaeA may have evolved specifically to detoxify this plant-derived compound

• Non-pathogenic bacteria may prioritize efflux of environmental toxins over antibiotics

Contribution to Ecological Fitness:
Research with other Erwinia species has shown that mutations affecting metabolism significantly impact host colonization . For E. tasmaniensis AaeA:

• Construct deletion mutants and assess plant colonization efficiency

• Compare survival in presence of plant extracts between wild-type and ΔaaeA strains

• Evaluate competitive fitness in mixed populations of wild-type and mutant

• Assess biofilm formation and host adhesion capabilities

E. tasmaniensis has been shown to reduce nitrates to nitrites, unlike some other Erwinia species , suggesting metabolic adaptations to its niche. The role of efflux pumps like AaeA in this ecological context may represent evolutionary specialization for non-pathogenic plant association rather than virulence.

How can structural information about AaeA inform the development of novel efflux pump inhibitors?

Structural insights into AaeA could guide rational drug design approaches for efflux pump inhibitors:

Critical Structural Features for Inhibitor Design:

• Substrate binding pocket architecture determines specificity

• Conformational changes during transport cycle present dynamic targeting opportunities

• Conserved residues across homologs indicate essential functional sites

• Interface regions with partner proteins offer alternative targeting strategies

Structure-Based Virtual Screening Approach:

• Generate refined homology models based on crystal structures of related transporters

• Perform molecular dynamics simulations to identify stable binding pockets

• Use computational docking to screen virtual compound libraries

• Prioritize hits based on predicted binding energy and druglikeness properties

• Synthesize or acquire top candidates for experimental validation

Fragment-Based Design Strategy:
For novel scaffolds:

• Identify small molecular fragments that bind to different sites on AaeA

• Use NMR, X-ray crystallography, or computational methods to verify binding

• Link or grow fragments to create high-affinity inhibitors

• Optimize for physicochemical properties and bacterial penetration

Rational Modification Approach:
Based on known substrates:

• Start with p-hydroxybenzoic acid structure as a template

• Systematically modify functional groups to improve binding affinity

• Add features that prevent efflux (size, rigidity, binding irreversibility)

• Balance membrane penetration with binding site affinity

Research on MATE efflux pumps has demonstrated the feasibility of inhibiting these transporters . The detailed amino acid sequence of AaeA (310 residues) provides a starting point for structural prediction and analysis. Combining this information with experimental data on substrate specificity could guide development of selective inhibitors that may be useful as research tools or as leads for antimicrobial development.

How might CRISPR-Cas9 genome editing be applied to study AaeA function in E. tasmaniensis?

CRISPR-Cas9 technology offers unprecedented precision for genetic manipulation of bacterial systems:

Methodological Approach for AaeA Functional Studies:

• Design sgRNAs targeting aaeA gene with minimal off-target effects

• Construct CRISPR delivery vectors compatible with E. tasmaniensis

• Introduce mutations ranging from complete knockouts to specific amino acid substitutions

• Create reporter fusions at the native locus without disrupting regulation

Advanced Applications:

• CRISPRi (CRISPR interference) for tunable repression of aaeA expression

• CRISPRa (CRISPR activation) to upregulate expression for gain-of-function studies

• Base editing to introduce specific mutations without double-strand breaks

• Multiplex editing to simultaneously modify aaeA and partner genes

Validation and Phenotypic Analysis:

• Confirm mutations by sequencing and expression analysis

• Assess impact on substrate transport using fluorescent dye accumulation

• Evaluate changes in resistance to antimicrobial compounds

• Measure fitness in various environmental conditions

Recent studies have demonstrated the use of CRISPR-based approaches to study bacterial efflux systems. The diversity of CRISPR profiles observed in Erwinia species suggests these techniques could be adapted for E. tasmaniensis . This would enable precise dissection of AaeA function in its native context.

What insights can single-cell techniques provide about heterogeneity in AaeA expression and function?

Bacterial populations exhibit significant cell-to-cell variability in gene expression and phenotypes, which may be particularly relevant for stress response systems like efflux pumps:

Single-Cell Analysis Approaches:

• Fluorescent reporter fusions (aaeA-gfp) to visualize expression heterogeneity

• Flow cytometry to quantify expression levels across thousands of individual cells

• Microfluidics to monitor dynamic responses to environmental changes

• Single-cell RNA-Seq to profile transcriptome-wide variability

Key Research Questions Addressable by Single-Cell Methods:

• Does AaeA expression follow all-or-none or graded patterns in response to inducers?

• Do subpopulations with higher AaeA expression serve as "persister" cells during stress?

• How does AaeA expression correlate with other stress response systems?

• Is there spatial organization of AaeA expression in bacterial communities or biofilms?

Methodological Considerations:

• Use photoconvertible fluorescent proteins to track expression history

• Combine with time-lapse microscopy to monitor dynamic responses

• Correlate with single-cell phenotypic assays (growth rate, survival)

• Apply computational modeling to understand population-level consequences

Single-cell approaches have revealed important insights about heterogeneity in antibiotic resistance mechanisms. Similar techniques applied to AaeA in E. tasmaniensis could reveal how non-pathogenic bacteria employ efflux systems as part of their adaptive strategy in plant environments.

How does the prophage content of Erwinia genomes influence efflux pump evolution and function?

Recent genomic analysis has revealed that prophages are abundant elements integrated into Erwinia genomes and contribute to inter-strain genetic variability . This raises important questions about their impact on efflux systems:

Research Approaches to Explore Phage-Efflux Relationships:

• Comprehensive genomic analysis of prophage distribution in relation to efflux pump genes

• Evolutionary analysis to detect horizontal gene transfer events affecting efflux systems

• Experimental phage infection studies to assess impact on efflux pump expression

• Comparative analysis of efflux efficiency between strains with different prophage content

Key Questions:

• Are efflux pump genes carried on prophages or genomic islands in some Erwinia strains?

• Do prophages influence the regulation of chromosomally-encoded efflux systems?

• Has phage-mediated horizontal gene transfer contributed to efflux pump diversity?

• Could phage integration disrupt or enhance existing efflux systems?

Experimental Design Considerations:

• Use whole-genome sequencing to characterize prophage content across Erwinia species

• Compare efflux gene sequences from prophage-containing and prophage-free regions

• Employ transcriptomics before and after prophage induction

• Create isogenic strains with and without specific prophages to assess functional impact

Recent studies have shown differential distribution of prophages within the Erwinia genus, with some species like E. tasmaniensis showing lower prevalence of intact prophages compared to species like E. tracheiphila . Understanding how this prophage diversity influences efflux pump evolution could provide insights into the adaptive strategies of different Erwinia species in their respective ecological niches.