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POSTERS: Fungicide and antibiotic resistance

Study of copper tolerance and resistance genes copA and copB in the plant pathogen Xylella fastidiosa
Qing Ge - Auburn University. Paul Cobine- Auburn University, Leonardo De La Fuente- Auburn University

Xylella fastidiosa (Xf), a Gram-negative bacterium, is a xylem-limited plant pathogen that causes diseases worldwide in many economically important crops such as grape. Copper (Cu)-containing antimicrobials are widely used in Xf hosts in vineyards and orchards. The accumulation of Cu in field soil and plants could be a challenge for Xf survival. Here we define Cu tolerance as the ability to growth under chronic elevated Cu levels while Cu resistance is the ability to survive acute Cu stress. Cu-genes copA and copB have been studied in model bacteria E. coli and plant pathogenic bacteria Pseudomonas spp. However, the functions of these genes differ among bacterial species, and the mechanisms of Cu tolerance/resistance is still unclear in Xf. Here we study copA and copB function in Xf through site-directed mutagenesis. Both copA and copB mutants were more sensitive to Cu than wild-type (WT) Xf strains. During acute exposure to high concentrations of Cu, the copA mutant showed significantly lower survival, while the copB mutant did not differ from WT. Under chronic Cu stress, the copA mutant shows sensitivity to Cu concentration at 0.125 mM while copB mutant is sensitive to 0.030 mM Cu. We hypothesize that copA and copB function differently towards Cu tolerance/resistance in Xf. CopA likely works as an oxidase to help Cu detoxification, while CopB is a putative Cu exporter. Future studies will address the Cu-binding capacity of CopA and CopB, and damage caused by Cu in the mutants. This will help to develop disease management strategies against this plant pathogen.