Physical map of the chromosome of the phytopathogenic bacterium Pseudomonas syringae pv. phaseolicola.

pv. (P.s. phaseolicola) is one of about 45 recognized pathovars within the group and is the causal agent of halo-blight disease of beans. DNA from this bacterium digested to completion with two different restriction enzymes, I and I, yielded 15 and 16 fragments, respectively. These were separated using PFGE and sized by comparison to known molecular mass markers. The chromosome was determined to be approximately 5.64 Mb in size. To link the different fragments obtained into a circular chromosome map for both enzymes, 150 random Tn mutants of were used as a source of DNA and the identification of the band carrying the transposon 'tag' in each mutant was done after PFGE and Southern hybridization of a complete chromosomal digestion using a Tn probe. Partial digestions of DNA from different Tn mutants 'tagging' specific bands were then generated and the complete and partial products of the digestion separated by PFGE and identified with a Tn probe. By calculating the size of the partial products, it was then possible to link different bands into a physical map. This is the first report on the construction of a physical map of a member of the P. syringae group and should be invaluable for molecular genetic analysis in this species and in evolutionary or taxonomic studies when compared to similar data obtained for any of the other recognized pathovars.