Researchers at the University of Otago – Ōtākou Whakaihu Waka have published a CRISPR-based method for systematically disrupting genes across entire bacteriophage genomes, a workflow they say can identify essential phage genes and deliver new genetic cargo in a single pipeline. The study, "Defining the essential genome of diverse phages with phage Tn-seq," appeared in Nature Microbiology.

The method merges two established technologies: transposon insertion sequencing (Tn-seq) and CRISPR–anti-CRISPR selection. A transposon jumps into a phage genome and disrupts a gene. The selection system then recovers phages carrying those mutations, letting researchers determine which genes tolerate disruption and which are essential for the virus to survive.

That readout addresses a practical bottleneck in phage R&D portfolios. Many phage genes encode unknown functions, which makes it difficult to predict how candidate viruses behave or to modify them reliably for therapeutic or biotechnology programs.

Why does the 'dark matter' problem matter for phage pipelines?

Senior author Peter Fineran, PhD, puts the field's state of knowledge in blunt historical terms.

"Our knowledge of phages is probably like the understanding of antibiotics back in the 1950s," Fineran said. "Many phage genes are currently in the area of microbial dark matter—encoding functions we just don't understand—which is limiting our ability to use phages in healthcare and biotechnology."

For teams evaluating phage-based approaches to antimicrobial resistance or alternatives to agrochemicals, uncharacterized genes translate directly into regulatory and engineering risk. A genome-wide essentiality map reduces that uncertainty before candidates reach development.

What else can the platform do beyond gene disruption?

After establishing the mutagenesis workflow, the group repurposed the transposon as a delivery vehicle. Rather than using it only to knock out genes, they loaded it with an additional sequence and inserted a fluorescent marker into phage genomes.

"Once we had that established, we thought we could expand the technique and also use it to add genes directly into the phage genomes," co-lead author Manuela Fuchs, PhD, said.

The same cargo-delivery mechanism could insert genes that help phages overcome bacterial defense systems, potentially improving their effectiveness against target pathogens — a direct lever on potency for therapeutic programs.

Senior author Leah Smith, PhD, framed the platform's value proposition in budget-relevant terms: "This is a systematic, broadly applicable, and cost-effective way to not only investigate gene function, but also rapidly engineer phage genomes."

What are the limits?

The published results cover workflow establishment and a proof-of-concept marker insertion, not clinical data. The authors state that engineered phages would still require further testing to establish safety and effectiveness in specific applications. Claims of broad applicability across diverse phages rest on the method's design — transposon mutagenesis plus selection — rather than on demonstrated coverage of every phage family.

For R&D managers, the platform serves two portfolio functions: mapping uncharacterized phage genomes for fundamental studies, and building variants with new capabilities on a compressed timeline. The next step for the Otago group and its adopters will be applying the workflow to therapeutically relevant phages and testing engineered variants against bacterial defense systems in controlled infection models.