EXTENDING FILAMENTOUS PHAGE HOST-RANGE BY THE GRAFTING OF A HETEROLOGOUS RECEPTOR-BINDING DOMAIN

fd and IKe are two similar filamentous phage which infect their hosts by means of pili found on the host membrane: fd infects bacteria beari ng F pili, whereas IKe infects bacteria bearing N or I pili. Infection is mediated by the gene 3 protein (g3p), which of the nine proteins f ound in both phage is the most diverse. Previous attempts to incorpora te g3p from one phage into the other by complementation have been unsu ccessful [Bross et al. (1988) J. Gen. Microbiol. 134, 461-471]. Here w e have grafted different parts of IKe g3p to the end of fd g3p and so augmented the host range of fd phage. We show that phage bearing such chimeric g3p are able to infect bacteria bearing both N and F pili pro viding they contain at least the receptor domain of IKe g3p, the infec tion of N bearing bacteria occurring at a level 70 000 times greater t han background. This level of infection can be increased tenfold by in cluding the glycine-rich domain as well. Addition of the penetration d omain does not improve the level of infection above that of the recept or domain alone, indicating that the fd penetration domain is function al in the infection of bacteria bearing either N or F pili. Similarly derived fd phagemid also show increased infection of bacteria bearing N pili, albeit at much lower levels, suggesting that efficient infecti on requires more than one functional g3p on the surface of the phage.