Genetic mapping of mutations in independently isolated nontoxinogenic mutants of Vibrio cholerae

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Abstract
Conjugal mating experiments were performed between donor strains of V. cholerae carrying the vibrio sex plasmid P and recipient strains lacking the P plasmid. Donor and recipient genotypes differed with respect to toxinogenicity (tox), nutritional requirements and antibiotic susceptibilities. Recombinants carrying selected donor and recipient markers were produced at low frequencies in conjugal matings. Mapping of tox markers was accomplished by scoring for the frequency of coinheritance of the donor tox allele with selected and unselected donor markers. Four independently isolated tox markers were analyzed. Each of these 4 tox markers was linked to the his-1 site in linkage group I on the genetic map of V. cholerae. In matings between a recipient strain carrying the tox-1 marker and donor strains carrying tox-2, tox-3 or tox-4, all selected his+ recombinants remained nontoxinogenic. Matings between multiply marked strains demonstrated that the position of tox-1 with respect to other genetic loci in linkage group I is as follows: met-2.sbd.trp-1.sbd.asp-1.sbd.nal-1.sbd.his-1.sbd.tox-1. A chromosomal determinant linked to his-1 in linkage group I on the genetic map of V. cholerae is probably essential for toxinogenesis and tox-1, tox-2, tox-3 and tox-4 may be alleles of a single tox gene.