Transduction frequency with phage P1 had been observed to be very low in Escherichia coli K-12 mutants lacking the operon (ppk1-ppx) responsible for the synthesis of inorganic polyphosphate (poly P). We now find that these mutants, for lack of poly P, are lysogenic for P1 and when infected with phage P1 produce only approximately 1% the number of infective centers compared with the WT host. Both phage adsorption and release were unaffected. The host-encoded P1 late-gene transcriptional activator, SspA, failed to show the transcriptional increase in the mutant, observed in the WT. UV induction of a P1-infected mutant resulted in a 200-fold increase in the production of infectious phage particles. The lysogenized P1 (P1mut) and P1 progeny from the mutant host (Deltappk1-ppx) produced plaques of differing morphologies, whereas P1 progeny from the WT yielded only small, clear plaques. Two discernable variants, one producing small and clear plaques (P1small) and the other large plaques with turbid rims (P1large), had broader host range and produced larger burst sizes in WT compared with P1. Transmission electron microscopy showed P1mut had contractile sheath defects. Thus, the lack of poly P/PPK1 in the mutant host resulted in the formation of defective P1 particles during intracellular growth. A filamentous phage, fd, also failed to produce plaques on a mutant lawn. Although fd adsorbed to the F-pilus, its DNA failed to enter the mutant host.