This study presents the high-resolution cryo-electron microscopy (cryo-EM) structures of bacteriophage lambda tail complexed with its irreversible Shigella sonnei 3070 LamB receptor and the closed central tail fiber. These structures reveal the molecular mechanisms underlying the initial interaction between bacteriophage lambda and its host, which is crucial for infection. The study shows that binding of the lambda tail to LamB triggers a significant conformational change in the tail tip, leading to the irreversible adsorption of the phage and subsequent DNA injection. The structures also highlight the role of the gpJ protein, a key component of the lambda baseplate, in the interaction with the bacterial receptor LamB. The gpJ protein, which includes a receptor-binding domain (RBD), undergoes structural changes upon binding to LamB, facilitating the transition from a closed to an open state. This structural change is essential for the phage to initiate infection by forming a transmembrane channel through which DNA can be injected into the host cell. The study provides detailed insights into the structural dynamics of the lambda phage tail and its interaction with the bacterial receptor, contributing to the understanding of bacteriophage-host interactions and their implications for microbiology and therapeutic development. The findings also suggest that the binding of the phage to the bacterial receptor triggers a series of structural changes that enable the phage to carry out its infection process. The study's results are supported by cryo-EM data and biochemical assays, which confirm the structural changes and functional roles of the various components of the lambda phage tail in the infection process. The research highlights the importance of understanding the molecular mechanisms of bacteriophage-host interactions for the development of phage-based therapies and the study of microbial infections.This study presents the high-resolution cryo-electron microscopy (cryo-EM) structures of bacteriophage lambda tail complexed with its irreversible Shigella sonnei 3070 LamB receptor and the closed central tail fiber. These structures reveal the molecular mechanisms underlying the initial interaction between bacteriophage lambda and its host, which is crucial for infection. The study shows that binding of the lambda tail to LamB triggers a significant conformational change in the tail tip, leading to the irreversible adsorption of the phage and subsequent DNA injection. The structures also highlight the role of the gpJ protein, a key component of the lambda baseplate, in the interaction with the bacterial receptor LamB. The gpJ protein, which includes a receptor-binding domain (RBD), undergoes structural changes upon binding to LamB, facilitating the transition from a closed to an open state. This structural change is essential for the phage to initiate infection by forming a transmembrane channel through which DNA can be injected into the host cell. The study provides detailed insights into the structural dynamics of the lambda phage tail and its interaction with the bacterial receptor, contributing to the understanding of bacteriophage-host interactions and their implications for microbiology and therapeutic development. The findings also suggest that the binding of the phage to the bacterial receptor triggers a series of structural changes that enable the phage to carry out its infection process. The study's results are supported by cryo-EM data and biochemical assays, which confirm the structural changes and functional roles of the various components of the lambda phage tail in the infection process. The research highlights the importance of understanding the molecular mechanisms of bacteriophage-host interactions for the development of phage-based therapies and the study of microbial infections.