The saclayvirus Aci01-1 very long and complex fiber and its receptor at the Acinetobacter baumannii surface

The Acinetobacter baumannii bacteriophage Aci01-1, which belongs to the genus Saclayvirus of the order Caudoviricetes, has an icosahedral head and a contractile rigid tail. We report that Aci01-1 has, attached to the tail conical tip, a remarkable 146-nm-long flexible fiber with seven beads and a terminal knot. Its putative gene coding for a 241.36-kDa tail fiber protein is homologous to genes in Aci01-1-related and unrelated phages. Analysis of its 3D structure using AlphaFold provides a structural model for the fiber observed by electron microscopy. We also identified a putative receptor of the phage on the bacterial capsule that is hypothesized to interact with the Aci01-1 long fiber.