Copper (Cu) is an essential element that can be toxic if homeostasis is disrupted. Xylella fastidiosa, a xylem-limited plant pathogenic bacterium that causes disease in many economically important crops worldwide, has been exposed to Cu stress caused by wide application of Cu-containing antimicrobials used to control other diseases. However, X. fastidiosa Cu homeostasis mechanisms are still poorly understood. The potentially Cu-related protein CutC, which is involved in Cu tolerance in Escherichia coli and humans, has not been analyzed functionally in plant pathogenic bacteria. We demonstrate that recombinantly expressed X. fastidiosa CutC binds Cu and deletion of cutC gene (PD0586) in X. fastidiosa showed increased sensitivity to Cu-shock compared with wild type (WT) strain TemeculaL. When infecting plants in the greenhouse, cutC mutant showed decreased disease incidence and severity compared with WT but adding Cu exaggerated severity. Interestingly, the inoculation of cutC mutant caused reduced symptoms in the acropetal regions of plants. We hypothesize that X. fastidiosa cutC is involved in Cu homeostasis by binding Cu in cells, leading to Cu detoxification, which is crucial to withstand Cu-shock stress. Unveiling the role of cutC gene in X. fastidiosa facilitates further understanding of Cu homeostasis in bacterial pathogens.
Keywords: Cu homeostasis; Xylella fastidiosa; cutC genes; plant–bacteria interaction; virulence; xylem pathogen.