A study published in Nature (DOI: 10.1038/s41586-024-07681-w) describes a method for in situ base editing of bacteria in the mouse gut. Researchers engineered a phage-derived particle to deliver a base editor and modify Escherichia coli colonizing the mouse gut. Editing of a β-lactamase gene in a model E. coli strain resulted in a median editing efficiency of 93% of the target bacterial population with a single dose. Edited bacteria were stably maintained in the mouse gut for at least 42 days following treatment. This was achieved using a non-replicative DNA vector, preventing maintenance and dissemination of the payload. The approach was then used to edit several genes of therapeutic relevance in E. coli and Klebsiella pneumoniae strains in vitro and demonstrate in situ editing of a gene involved in the production of curli in a pathogenic E. coli strain. The study demonstrates the feasibility of modifying bacteria directly in the gut, offering a new avenue to investigate the function of bacterial genes and opening the door to the design of new microbiome-targeted therapies. The research highlights the potential of using phage-derived particles for targeted genetic modifications in the gut environment, with the ability to deliver and edit genes in bacteria without the need for selection pressure or maintenance of a transgene. The study also shows that the non-replicative payload allows for efficient editing of a target bacterial population without spreading transgenes. The findings suggest that this approach could be used to modify bacteria in the gut for therapeutic purposes, such as targeting pathogenic strains or modifying genes involved in disease processes. The study also discusses the potential of this approach for future applications, including the development of new microbiome-targeted therapies and a deeper understanding of bacterial gene functions in both health and disease.A study published in Nature (DOI: 10.1038/s41586-024-07681-w) describes a method for in situ base editing of bacteria in the mouse gut. Researchers engineered a phage-derived particle to deliver a base editor and modify Escherichia coli colonizing the mouse gut. Editing of a β-lactamase gene in a model E. coli strain resulted in a median editing efficiency of 93% of the target bacterial population with a single dose. Edited bacteria were stably maintained in the mouse gut for at least 42 days following treatment. This was achieved using a non-replicative DNA vector, preventing maintenance and dissemination of the payload. The approach was then used to edit several genes of therapeutic relevance in E. coli and Klebsiella pneumoniae strains in vitro and demonstrate in situ editing of a gene involved in the production of curli in a pathogenic E. coli strain. The study demonstrates the feasibility of modifying bacteria directly in the gut, offering a new avenue to investigate the function of bacterial genes and opening the door to the design of new microbiome-targeted therapies. The research highlights the potential of using phage-derived particles for targeted genetic modifications in the gut environment, with the ability to deliver and edit genes in bacteria without the need for selection pressure or maintenance of a transgene. The study also shows that the non-replicative payload allows for efficient editing of a target bacterial population without spreading transgenes. The findings suggest that this approach could be used to modify bacteria in the gut for therapeutic purposes, such as targeting pathogenic strains or modifying genes involved in disease processes. The study also discusses the potential of this approach for future applications, including the development of new microbiome-targeted therapies and a deeper understanding of bacterial gene functions in both health and disease.