Homologous Recombination for Phage Genome Engineering

Service Overview

Homologous recombination is well suited to local phage genome edits when the target locus is defined and a viable recombinant can be recovered in a compatible phage-host system. A correct donor design alone is not enough: DNA delivery, recombination frequency, locus function, packaging constraints, host genetics, and the fitness effect of the edit can all influence recovery.

We begin with feasibility rather than applying a fixed editing recipe. If the target-locus sequence or annotation is incomplete, phage genome sequencing and genome annotation can reduce uncertainty before donor construction. For extensive or dispersed changes, synthetic phage genome design or an assembly-based route may provide a more practical path.

Which Phage Genome Engineering Route Fits Your Edit?

Choose the engineering route according to edit scale, host and DNA-delivery compatibility, and how the recombinant will be recovered. The options below address different project constraints rather than interchangeable workflows.

Which Phage Genome Engineering Route Fits Your Edit? comparison table
Engineering Route	Best Fit	Key Consideration
Homologous Recombination	Defined local insertions, deletions, replacements, or sequence changes	Recombinant recovery can be limiting
Recombineering of Electroporated DNA	Targeted edits where direct donor/genome delivery is suitable	DNA delivery and host/phage compatibility
In Vivo Phage Recombineering	Host-based recombination workflows	Recombination-system compatibility
Spacer-Guided Nuclease-Assisted Engineering	Projects that benefit from parental counterselection	Targeting sequence constraints and escape
Whole-Genome Synthesis and Assembly	Extensive redesign or multiple dispersed changes	Genome assembly and phage rescue
Yeast-Based / Cell-Free Assembly	Large synthetic genome construction	Assembly and reboot compatibility

For broader redesign, Cell-Free Assembly of Phage Genomes offers another assembly route. The most suitable method is the one that provides a realistic path from DNA design to a recoverable clonal phage.

Homologous Recombination Project Design

Before construction, the edit, host, donor, and recovery strategy are considered together. The goal is not only a valid recombination substrate, but an engineered phage that can be recovered, isolated, and confirmed.

Genome and Target Locus - A complete or sufficiently resolved locus sequence is used to define edit boundaries and review nearby genes, promoters, terminators, overlapping coding regions, and packaging-related features.
Propagation Host - Host compatibility is assessed for both phage propagation and the selected recombination context. Host genotype can affect recombination, DNA processing, and donor delivery.
Edit Type and Scale - Local insertions, deletions, replacements, and sequence changes are reviewed against locus function, genome size, and likely fitness effects. Extensive or dispersed edits may be better suited to an assembly-based route.
Donor and Homology Design - The intended change is placed between project-appropriate homologous regions, with reading frame, local regulatory architecture, neighboring sequence, repeats, and relevant packaging constraints considered in the design.
Recovery Strategy - Screening is planned before donor construction. PCR, phenotype, hybridization, sequencing, or compatible parental counterselection can be selected according to the edit. A silent screening signature may be considered only when scientifically justified and compatible with the locus.

Recombinant Qualification and Genotype Confirmation

A positive signal in a mixed lysate does not establish a clonal engineered phage. Recombinants may be rare within a larger parental population, and a primary plaque can contain more than one genotype. Qualification therefore focuses on isolating and confirming the engineered clone.

Candidate Identification - PCR, phenotype, hybridization, or another edit-specific assay can identify plaques or populations that may contain the desired genotype.
Plaque Purification - Candidate plaques are isolated and propagated to separate the recombinant from parental particles. Mixed signals or heterogeneous sequence traces can indicate that another purification round is needed.
Local Genotype Confirmation - Junction PCR, locus-spanning PCR, and Sanger sequencing can confirm local insertions, deletions, replacements, or sequence changes.
Broader Sequence Integrity - phage genome sequencing can be added when confirmation beyond the edited locus is important.

Our Homologous Recombination Engineering Workflow

The workflow links edit design with recombinant recovery and clonal confirmation rather than treating homologous exchange as the endpoint.

01

Feasibility and Edit Design

Finalize the phage-host context, target locus, intended sequence change, donor architecture, and recombinant-recovery assay.
02

Donor Construction

Build and sequence-verify the donor carrying the intended edit between project-appropriate homologous regions.
03

Host-Based Recombination

Introduce the donor into a compatible host and recombination context and allow homologous exchange with the phage genome.
04

Recombinant Screening and Plaque Isolation

Screen or enrich the mixed progeny, identify candidate recombinants, and isolate plaques from parental or escape backgrounds.
05

Clonal Genotype Confirmation

Purify candidate plaques to clonality as needed and confirm the engineered locus by PCR, Sanger sequencing, or broader sequencing according to edit scale and project risk.

Project Inputs and Deliverables

Project Inputs

What to Send Us

Phage and Host -
Phage identity, propagation host, and the complete genome sequence if available.
Edit Specification -
Target locus and the exact insertion, deletion, replacement, or sequence change required.
Known Constraints -
Available information on essentiality, local regulation, packaging limits, or expected fitness effects.
Recovery Context -
Any preferred screening or selection approach, existing assay, or prior engineering result that may affect recombinant recovery.
Project Endpoint -
Whether the project requires a genotype-confirmed recombinant only or downstream functional characterization.

Project Outputs

What You Receive

Donor Design or Construct -
The agreed donor architecture and sequence-verified construct when included in scope.
Recombinant Screening Results -
Records of the edit-specific screening and plaque-isolation route used to identify candidate recombinants.
Plaque-Purified Phage -
Clonal phage material when a viable recombinant is recovered and material delivery is included in scope.
Genotype Confirmation -
Local sequence confirmation, with broader sequencing added when agreed for the project.
Technical Report -
A summary of the design, recovery, purification, and confirmation results.

Exact deliverables depend on the edit and phage-host system. No universal editing efficiency or fixed number of plaque-purification rounds is assumed.

Optional Functional Characterization

Genotype confirmation establishes that the intended DNA change is present; it does not establish the biological effect of the edit. Changes to receptor-binding proteins, structural components, promoters, lysis genes, or other functions may require phenotype-level testing.

Depending on the hypothesis, genotype-confirmed material can proceed to host-range determination, adsorption-rate measurement, or one-step growth curve analysis. A parental comparator is useful when the goal is to attribute a phenotype to the engineered change.

Broader genome sequencing can be added when whole-genome sequence integrity matters. For larger synthetic constructs, synthetic phage genome rescue and functional identification or design and production of engineered synthetic phages may provide a more suitable route than iterative local editing.

Published Data

Workflow diagram showing donor-mediated phage recombineering, spacer-guided parental counterselection, recovery of primary plaques, PCR screening for the engineered allele, and secondary plaque purification for genotype confirmation (OA Literature) — Fig.1 Recombineering, parental counterselection, plaque screening, and recombinant purification.¹

Wetzel and colleagues described phage engineering workflows that combine recombineering with spacer-guided nuclease counterselection to reduce parental background during recovery of engineered mycobacteriophages. Their Figure 1 follows the path from a synthetic donor with homologous flanks to mixed progeny, parental counterselection, PCR screening of primary plaques, and re-isolation of a confirmed recombinant. The study also notes that traditional recombineering can produce mixed primary plaques and that difficult insertions or replacements may require extensive screening when counterselection is unavailable. These observations support treating recombinant recovery, plaque purification, and genotype confirmation as core engineering stages rather than post hoc checks. Reported efficiencies remain specific to the phage-host systems and selection designs studied and should not be treated as guaranteed success rates for other bacteriophages.

Frequently Asked Questions

Is homologous recombination suitable for every bacteriophage?

No. Suitability depends on phage replication biology, host compatibility, target-locus context, donor delivery, recombinant viability, and the practical ability to separate recombinant from parental phage.

Does a longer homology arm always improve recombinant recovery?

Not necessarily. Homology requirements are system dependent, and recovery also depends on DNA delivery, locus context, recombination functions, phage fitness, and the screening strategy.

How are recombinant phages separated from parental phages?

Depending on the edit, candidate recombinants can be identified by phenotype, edit-specific PCR, sequencing, or compatible parental counterselection. Single-plaque isolation is then used to associate the confirmed genotype with clonal phage material.

Why can a positive PCR from a lysate be insufficient?

A mixed lysate can contain both parental and recombinant genomes. PCR may detect the desired allele without showing that a purified plaque contains only the engineered genotype.

When should an assembly-based engineering route be considered instead?

Whole-genome synthesis or assembly may be more practical for extensive redesign, multiple dispersed changes, or an edit scale that makes iterative local recombination inefficient.

Does genotype confirmation prove the intended phenotype?

No. Sequence confirmation establishes the DNA change. Host range, adsorption, replication kinetics, stability, or another functional readout must be measured separately when those outcomes matter.

Reference

1. Wetzel, Katherine S., et al. CRISPY-BRED and CRISPY-BRIP: Efficient Bacteriophage Engineering. Scientific Reports 11 (2021): article 6796. Distributed under Open Access license CC BY 4.0, without modification. https://doi.org/10.1038/s41598-021-86112-6.

Homologous Recombination-mediated Phage Genome Engineering

Homologous Recombination-mediated Phage Genome Engineering

Homologous Recombination-Mediated Phage Genome Engineering