An amino acid substitution in a capsid protein enhances phage survival in mouse circulatory system more than a 1000-fold

In experiments with germ free mice, free from adaptive antibodies to the bacterial virus λ phage, titers of the virus in the circulatory system have been reported to decrease by more than 109 pfu within 48 h of intraperitoneal intravenous or oral administration. Based on these observations, serial passage techniques have been used to select λ phage mutants, with 13,000–16,000-fold greater capacity to remain in the mouse circulatory system 24 h after intraperitoneal injection. In these prior studies the “long-circulating” phage, designated λArgo phage, had at least three mutations including one in the major phage capsid (E) protein, which resulted in the change of glutamic acid to a lysine at residue 158. In the current study, we demonstrate that this single specific substitution in the E protein is sufficient to confer the “long-circulating” phenotype. The isogenic pair of phage developed in this study consisting of the long-circulating marker-rescued λArgo phage, and the parental wild type phage can be used for studies of viral recognition mechanisms of the innate immune system and for the development of more effective antibacterial therapeutic phage strains.