Recombinant Aliivibrio salmonicida Probable intracellular septation protein A (VSAL_I1147)

What is the taxonomic context of Aliivibrio salmonicida and why is it significant for research?

Aliivibrio salmonicida (formerly Vibrio salmonicida) is the etiological agent of cold water vibriosis affecting sea-farmed fish species, including Atlantic salmon (Salmo salar), rainbow trout (Oncorhynchus mykiss), and Atlantic cod (Gadus morhua) . This bacterium has significant economic impact on aquaculture, though the disease is now largely controlled through vaccination .

The taxonomic reclassification from Vibrio to Aliivibrio occurred through phylogenetic analysis (Urbanczyk et al. 2007), positioning it in a group of marine bacteria that includes other species like Aliivibrio logei . Understanding the cell division proteins like VSAL_I1147 may provide insights into bacterial adaptation mechanisms in cold marine environments.

What expression systems are most effective for producing recombinant VSAL_I1147?

Based on available research, E. coli expression systems have been successfully used to produce recombinant VSAL_I1147 with an N-terminal His-tag . For optimal expression:

• Vector selection: pET-based expression vectors under T7 promoter control are recommended for high-yield expression

• Host strain optimization: BL21(DE3) derivatives optimize for membrane protein expression

• Induction parameters:

  • Temperature: 16-18°C for membrane proteins

  • IPTG concentration: 0.1-0.5 mM

  • Duration: Extended expression (12-16 hours)

For membrane proteins like VSAL_I1147, solubilization requires careful detergent selection. A systematic approach testing multiple detergents is recommended:

Each detergent should be evaluated for protein yield, purity, and retention of native structure through circular dichroism or fluorescence spectroscopy.

How can researchers assess the function of VSAL_I1147 in bacterial septation?

To investigate VSAL_I1147's role in septation:

• Knockout studies: Generate gene deletions in Aliivibrio salmonicida using homologous recombination or CRISPR-Cas9

• Complementation assays: Rescue knockout phenotypes with plasmid-expressed wild-type or mutant VSAL_I1147

• Microscopy techniques:

  • Phase contrast to observe cell morphology changes

  • Fluorescence microscopy with membrane dyes (FM4-64)

  • Time-lapse imaging to track septation dynamics

• Co-localization studies: Express fluorescently tagged VSAL_I1147 along with other known septation proteins to observe spatial and temporal relationships during cell division

Given that Aliivibrio salmonicida grows optimally at lower temperatures (7.5°C as noted in research), temperature-controlled imaging setups are essential for accurate in vivo characterization .

How might VSAL_I1147 interact with the quorum sensing systems in Aliivibrio salmonicida?

Aliivibrio salmonicida possesses complex quorum sensing (QS) systems that regulate biofilm formation and virulence through cell density-dependent mechanisms . While direct evidence linking VSAL_I1147 to QS hasn't been established in the available research, methodological approaches to investigate potential interactions include:

• Transcriptomic analysis: Compare VSAL_I1147 expression levels between wild-type and QS mutant strains (ΔainS, ΔluxI, ΔrpoQ) using RNA-seq or qRT-PCR

• Phenotypic assays with VSAL_I1147 overexpression or deletion in QS mutant backgrounds:

  • Biofilm formation (crystal violet staining)

  • Colony morphology (rugosity)

  • Motility assays (swimming, swarming)

• Protein-protein interaction studies:

  • Bacterial two-hybrid systems

  • Co-immunoprecipitation with known QS regulators

  • Pull-down assays using His-tagged VSAL_I1147

The extensive QS research in Aliivibrio salmonicida has identified key regulators like LuxI, AinS, and RpoQ that influence biofilm formation in a cell density and temperature-dependent manner . The research shows that at high cell density, biofilm formation is downregulated through QS mechanisms, potentially involving structural proteins like VSAL_I1147.

What approaches can be used to investigate VSAL_I1147's potential role in Aliivibrio salmonicida pathogenesis?

To investigate VSAL_I1147's role in pathogenesis:

• In vivo infection models:

  • Use Atlantic salmon as the natural host

  • Compare infection dynamics of wild-type vs. ΔVSAL_I1147 mutant

  • Measure bacterial loads, tissue distribution, and host survival

• Immunological profiling:

  • Assess recombinant VSAL_I1147 immunogenicity

  • Develop monoclonal antibodies against VSAL_I1147

  • Test for cross-reactivity with related fish pathogens

• Vaccine potential assessment:

  • Evaluate purified VSAL_I1147 as a subunit vaccine candidate

  • Compare with current oil-adjuvanted multi-component vaccines

  • Measure protective efficacy in challenge studies

Research has identified other Aliivibrio salmonicida membrane proteins, such as the 20 kDa peptidoglycan-associated lipoprotein (Pal) as immunogenic components recognized by antibodies from infected fish . Similar methodologies could be applied to assess VSAL_I1147's immunogenicity.

How does VSAL_I1147 compare to homologous septation proteins in other bacterial species?

To conduct comprehensive comparative analyses:

• Phylogenetic analysis workflow:

  • BLAST search to identify homologs across bacterial species

  • Multiple sequence alignment using MUSCLE or CLUSTALΩ

  • Construction of phylogenetic trees (Maximum Likelihood)

  • Analysis of evolutionary conservation patterns

• Structural comparison approaches:

  • Homology modeling of VSAL_I1147 using related structures as templates

  • Domain architecture analysis

  • Identification of conserved functional residues

  • Virtual docking studies with potential interaction partners

• Complementation studies:

  • Express VSAL_I1147 in model organisms with knockouts of homologous genes

  • Assess functional conservation by measuring restoration of normal septation

Based on homology to other bacterial septation proteins, VSAL_I1147 likely functions in the membrane during cell division, potentially participating in septum formation or regulation .

How can transcriptomic and proteomic approaches be combined to understand VSAL_I1147 regulation?

Integrative multi-omics approaches provide comprehensive understanding:

• Transcriptomic analysis:

  • RNA-seq under various conditions (temperature, growth phase, host interaction)

  • Identification of co-expressed gene clusters

  • Promoter analysis for regulatory elements

• Proteomic approaches:

  • Targeted proteomics (MRM-MS) to quantify VSAL_I1147 levels

  • Global proteomics to identify co-regulated proteins

  • Phosphoproteomics to detect potential post-translational modifications

• Data integration strategies:

  • Correlation analysis between transcript and protein levels

  • Network analysis to identify regulatory hubs

  • Pathway enrichment to place VSAL_I1147 in functional contexts

Previous research with Aliivibrio salmonicida has utilized transcriptomic approaches to study quorum sensing mutants (ΔlitR and ΔrpoQ), revealing differential expression of genes involved in motility, adhesion, and biofilm formation . Similar approaches could position VSAL_I1147 within these regulatory networks.

What methods are most effective for structural characterization of membrane-associated proteins like VSAL_I1147?

For structural studies of VSAL_I1147:

The amino acid sequence of VSAL_I1147 suggests transmembrane regions that would require specialized approaches for structural characterization .

What are the key unanswered questions about VSAL_I1147 that warrant further investigation?

Several critical research questions remain:

• Functional characterization:

  • Precise molecular function during bacterial cell division

  • Interaction partners in the septation machinery

  • Regulation in response to environmental signals

• Pathogenesis relevance:

  • Contribution to bacterial fitness during infection

  • Potential as a diagnostic marker or vaccine component

  • Role in environmental persistence outside the host

• Evolutionary significance:

  • Selection pressures shaping VSAL_I1147 in marine pathogens

  • Functional divergence from homologs in other Vibrio species

  • Adaptation to cold-water environments