Non-receptivity for ϰ phage of ϰ-lysogenic Serratia and reactions to superinfection of receptive cells with a mutant prophage

Summary

ϰ l_I-lysogenic cells of Serratia marcescens as opposed to l_I ⁺-lysogenic cells, are receptive to further ϰ infection. After superinfection with wild type or several clear plaque mutants killing and lytic response were observed to a varying extent. From some of the surviving cells doubly lysogenic colonies with a l_I ⁺ and a l_I prophage could originate, l_I ⁺ being dominant and the cells therefore non-receptive. By this property, combined with a special color reaction, the colonies could be easily screened. Evidence is presented that the l_I ⁺ gene product probably does not interfere with the formation of new phage receptors but that under its influence receptors are masked.

Two ϰ mutants resembling int^- mutants are described which only rarely give double lysogenization and prophage substitution following superinfection. The phage-coded function normally achieving these reactions is likely to work constitutively after superinfection. Transduction experiments performed with one of the two mutants pointed at integration of ϰ prophage into the host DNA near to the trp gene.