Mixed infections of Bacillus subtilis involving bacteriophage SPO2c 1 .

The synthesis of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) was studied in Bacillus subtilis cells mixedly infected with phages SPO2c(1) and either SP82 or beta22. It was found that cells preinfected 5 min with either beta22 or SP82 could not support significant amounts of RNA or DNA synthesis from the genome of superinfecting SPO2c(1). Conversely, cells preinfected with SPO2c(1) remained susceptible to superinfection even at the midpoint of the latent period. When SP82 was added to cells preinfected 5 min with SPO2c(1), the former greatly inhibited the replication and transcription of the SPO2c(1), DNA, but if superinfection with SP82 was delayed until the 15th min of the SPO2c(1) latent period, RNA and DNA specific for both phages were synthesized. Both viral genomes were transcribed throughout the remainder of the lytic cycle when beta22 was added to cells preinfected either 5 or 15 min with SPO2c(1). In both the SPO2c(1)-SP82 and the SPO2c(1)-beta22 mixed infections, the types of phage-specific RNAs synthesized at a given time in the latent period were similar to those synthesized in single infections with each phage. The association of SPO2c(1) DNA with the host cell membrane in certain of the doubly infected cells was different from that observed in singly infected cells. In the SPO2c(1)-SP82 infection, SPO2c(1) DNA was not released from the membrane; in the SPO2c(1)-beta22 mixed infections, significantly less SPO2c(1) DNA was membrane-bound when beta22 was added before SPO2c(1). However, binding and release of SPO2c(1) DNA was normal in cells infected first with SPO2c(1) and then with beta22. The synthesis of phage-specific nucleic acids and the binding of phage DNA to the membrane are discussed with respect to dominance relationships among these phages.