The branched receptor-binding complex of Ackermannviridae phages promotes adaptive host recognition

Bacteriophages can encode multiple receptor-binding proteins, allowing them to recognize diverse receptors for infecting different strains. <i>Ackermannviridae</i> phages recognize various polysaccharides as receptors by encoding multiple tail spike proteins (TSPs), forming a branched complex. We aimed to mimic the evolution of the TSP complex by studying the acquisition of TSPs without disrupting the complex's functionality. Using kuttervirus S117 as a backbone, we demonstrated that acquiring <i>tsp</i> genes from <i>Kuttervirus</i> and <i>Agtrevirus</i> phages within the <i>Ackermannviridae</i> family led to altered host recognition. A fifth TSP was designed to interact with the branched complex and expand host recognition even further. Interestingly, the acquisition of <i>tsp5</i> resulted in a recombination event between <i>tsp4</i> and <i>tsp5</i> or deletion of <i>tsp3</i> and truncation of <i>tsp4</i> genes. Our study provides insight into the development of the branched TSP complex, enabling <i>Ackermannviridae</i> phages to adapt to different hosts.