Mechanism of phage PS166-mediated biotype conversion in Vibrio cholerae: Role of the hlyA locus

Temperate phage PS166 lysogens of Vibrio eltor MAK757 biotype eltor belong to two major categories. Seventy percent of the lysogens acquire auxotrophy for glycine and histidine and maintain their parental biotype. About 10% o f the lysogens become Cys(-) or Cys(-) Met(-) and are converted to the clas sical biotype with complete changes in all biotype-specific determinants. P CR and RFLP analysis revealed that in the latter lysogens, the phage genome integrated at the hlyA locus, whereas the same locus remained unaffected i n lysogens that retained their parental biotype. These results suggest that the two types of lysogens arose due to integration of the phage genome at two different locations on the chromosome. A restriction map of the phage g enome was constructed using Avail and Bg/11. An 800-bp Bg/11 fragment carry ing the attP site, located at one of the termini of the phage genome, was u sed to distinguish the two classes of lysogen. (C) 2000 Academic Press.