The branched receptor binding complex of Ackermannviridae phages promotes adaptative host recognition

Bacteriophages may express multiple receptor binding proteins, enabling the recognition of distinct and diverse bacterial receptors for infection of a broad range of strains. Ackermannviridae phages recognize diverse O-antigens or K-antigens as receptors by expressing multiple tail spike proteins (TSPs). These TSPs interact and form a branched protein complex protruding from the baseplate attached to the distal tail. Here, we aimed to mimic the evolution of the TSP complex by studying the acquisition of new TSPs without disrupting the functionality of the complex. Using kuttervirus phage S117 as a backbone, we demonstrated the acquisition of entire tsp genes from Kuttervirus and Agtrevirus phages within the Ackermannviridae family. A fifth TSP was designed to interact with the complex and provide new host recognition to expand the branched TSP complex. Interestingly, the acquisition of tsp5 resulted in new variants of the branched TSP complex due to the exchange or deletion of tsp genes. Overall, our study provides novel insight into the development of the branched TSP complex, enabling Ackermannviridae phages to adapt to new hosts.