SPP1 and infection: Several Caudovirales phages, such as P22, φ29 and HK97, have served as models for understanding the structure and assembly of phage capsids [29, 30], while particular Siphoviridae, including phages λ, T5, SPP1 and p2, have been instrumental in assessing the assembly and role of the tail during infection [26, 31–33].