Genetic basis of copper-tolerance in Australian Pseudomonas syringae pv. tomato

The genetic basis of copper-tolerance in Australian Pseudomonas syringae pv. tomato (Pst) was investigated through PCR assays and genome analysis. Seven PCR assays were tested targeting copper metabolising (cop) genes, this included previously published assays as well as three new assays. These assays varied in their ability to detect cop genes in copper tolerant isolates and no one set of primers tested amplified all isolates, however, there is potential for these to be developed further for diagnostic purposes. The genomes of three copper tolerant isolates were sequenced using the Illumina platform. The genome assemblies of these isolates identified putative Cop and CopR/CusS operons homologous to those previously characterised in Pst as mediators of copper-tolerance. Analysis also suggests that the Cop and CopR/CusS operons may be located on either plasmid or chromosomal DNA, depending on the isolate studied. An additional CopAB complex was identified in the genomic assemblies of the three Pst isolates, and was homologous to chromosomal CopA and CopB in a copper sensitive Pst reference genome. Other potential copper metabolising genes were also identified. This is the first genomic analysis of copper tolerant Pst isolated outside of America, with PCR assays and genetic analysis revealing that the genetics of copper-tolerance in Pst is complex and diverse.