Exclusion of temperature bacteriophage P22 by virulent bacteriophage MB78 of Salmonella typhimurium: competition for association with the replication complex.

MB78, a virulent bacteriophage of S. typhimurium does not allow other bacteriophages like P22 and 9NA to multiply in its presence. The exclusion of P22 by MB78 is found to be due to competition for common binding site(s) in the host cell membrane. As a result, P22 DNA fails to replicate in presence of MB78 DNA. Further, the sedimentation profile of P22 DNA in cells infected simultaneously with P22 and MB78 suggested fragmentation of P22 DNA. This may also contribute to the exclusion phenomenon.