Advancing Fast-Track Genome Engineering in Bacillus subtilis Phages

phages. Our approach uses CRISPR-Cas9 as a counter-selection system to isolate mutants of the model lytic siphovirus phage, SPP1. Efficient genome editing was achieved using homologous repair patches as short as 40 nucleotides, enabling streamlined patch construction and parallel engineering, resulting in highly accurate genome edits within a day. We applied QuickPhage to delete both essential and nonessential phage genes and to insert reporter genes. Protein production, such as GFP, was synthetically regulated using inducible systems without significantly affecting phage fitness, achieving induction levels of up to 400-fold. Time-series coinfection experiments with fluorescent protein expressing phages also revealed a highly efficient superinfection arrest mechanism that prevents reinfection as early as 13 min after initial infection. These findings highlight the potential of phages for protein production, opening new opportunities for metabolic engineering. This work also lays the foundation for systematic phage genome refactoring workflows and the development of phage-based tools for efficient DNA delivery, thereby expanding the synthetic biology toolbox for