Chromoome mapping of asteurella pseudotuberculosis by interrupted mating

Pasteurella pseudotuberculosis, containing the Escherichia coli plasmid F'lac, transferred its chromosome in an oriented manner to each of five multiply auxotrophic strains of P. pseudotuberculosis. In a mating system containing gelatin, glucose, and phosphate buffer, a maximum of 0.02% of the donor cells transferred lead markers. The donor population was counterselected with nalidixic acid. We established the entry time of seven markers as follows: proline (11 min); arginine (14 min); histidine (14 min); threonine (25 min); lysine (50 min); tyrosine (67 min); and tryptophan (77 min). However, an analysis of the inheritance of unselected markers did not support the simplest assumption that the chromosome was transferred as Origin... pro... arg his... thr... lys... tyr... trp.... The markers common to all five recipients, arg and his, were closely linked, but of the five other markers, each unique to a different recipient strain, only trp was linked to arg and his. Our data suggest that the Pasteurella chromosome is transferred in more than one linkage group.