European Journal of Plant Pathology (2012) 133, 949-963

Franklin Behlau, Blanca I. Canteros, Jeffrey B. Jones and James H. Graham (2012)
Copper resistance genes from different xanthomonads and citrus epiphytic bacteria confer resistance to Xanthomonas citri subsp. citri
European Journal of Plant Pathology 133 (4), 949-963
Abstract: Genetic exchange is considered to be an important process in the selective adaptation of microorganisms to shifting and challenging environmental conditions. As a consequence of the copious use of copper bactericides, many species of plant pathogenic bacteria, including Xanthomonas citri subsp. citri (Xcc), have developed resistance to copper. This study assesses whether copper resistant (Cu^R) strains of other Xanthomonas species and citrus epiphytic bacteria pose a risk for the development of copper resistance in Xcc. Cu^R epiphytic bacteria were isolated on MGY agar from citrus leaves collected in two citrus groves treated with copper bactericides in Florida. Horizontal gene transfer of copper resistance genes was investigated within different Xanthomonas species and from citrus epiphytic bacteria to Xanthomonas. Cu^R epiphytic bacteria from citrus were screened for the presence of copper resistance genes homologous to copL, copA and copB genes from Xcc and characterized regarding tolerance to copper. Copper resistance determinants from a citrus epiphytic strain of Stenotrophomonas maltophilia (Stm) were cloned and expressed in Xcc and other Xanthomonas strains. Copper resistance genes in Xcc were determined to be present on a large (~300 kb) conjugative plasmid. Cu resistance was transferred via conjugation from two copper resistant citrus strains, Xcc and X. alfalfae subsp. citrumelonis (Xac), and two tomato pathogens, X. euvesicatoria (Xe) and X. perforans (Xp), to Xcc. PCR analysis revealed that two Cu^R strains from citrus, an epiphytic Xanthomonas ssp. and a strain of Stm, harboured homologs of the copper resistance genes found in Cu^R Xcc. The introduction of copLAB gene cluster from Stm into different xanthomonads conferred copper resistance to sensitive strains of Xcc, Xac, Xe and Xp. Based on these results there is a low, but significant, likelihood of horizontal gene transfer of copper resistance genes from other xanthomonads or epiphytic bacteria to Xcc in nature.
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Link to article at publishers website
Database assignments for author(s): Jeffrey B. Jones, Franklin Behlau

Research topic(s) for pests/diseases/weeds:
pesticide resistance of pest

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Xanthomonas citri	Citrus (genus)