Excess production of phage λ delayed early proteins under conditions supporting high Escherichia coli growth rates

Abstract

Bacteriophage λ is unable to lysogenize Escherichia coli hosts harbouring the rpoA341 mutation due to a drastic reduction in transcription from CII-activated lysogenic promoters (p _E, p ₁ and p _aQ). In addition, the level of early transcripts involved in the lytic pathway of λ development is also decreased in this genetic background due to impaired N-dependent antitermination. Here, it is demonstrated that despite the reduced level of early lytic p _L- and p _R-derived transcripts, lytic growth of bacteriophage λ is not affected in rich media. The level of the late lytic, p _R-derived transcripts also remains unaffected by the rpoA341 mutation under these conditions. However, it was found that whilst there is no significant difference in the phage burst size in rpoA ₊ and rpoA341 hosts growing in rich media, phage λ is not able to produce progeny in the rpoA341 mutant growing in minimal medium, in contrast to otherwise isogenic rpoA ⁺ bacteria. Provision of an excess of the phage replication proteins O and P in trans or overproduction of the antitermination protein N restore the ability of phage λ to produce progeny in the rpoA341 mutant under the latter conditions. These results suggest that in rich media phage λ produces some early proteins in excess of that needed for its effective propagation and indicate that replication proteins may be limiting factors for phage lytic growth in poor media.