Copper depending inhibition of Xanthomonas sp by the siderophore pyochelin

ADLER, CONRADO; MARÍA FERNANDA POMARES; NATALIA CORBALÁN; DE CRISTÓBAL, RICARDO E.; VINCENT PAULA A.

Congreso; XLVI Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología molecular; 2010

In a screening for metabolites produced by soil and rhizosphere bacteria capable of inhibiting Xanthomonas citri pv citri we identified strains from the Pseudomonas genus able to inhibit this pathogen. After purification we were able to identify the active compound as pyochelin. Since this compound is a siderophore capable of chelating metal ions, we tested if the inhibitory effect could be dependent on metal ion chelation. We observed no reduct ion on MICs when Fe+3, Zn+2, Mg+2 were added but we significantly reduced its inhibitory effect by adding copper. Since pyochelin is active against Xanthomonas species but not active against other gram negatives such as E. coli and Salmonella, we thought that resistant strains might have siderophores that would allow them to overcome the presence of pyochelin. Indeed, we observed that E. coli became sensitive to pyochelin when the biosynthesis of enterochelin was impaired by a mutation in the entE gene. In addition, we observed Xanthomonas protection against pyochelin when we added partially purified enterochelin. This E. coli siderophore is reported to be involved in copper reduction making it more available for cell growth, so we hypothesized that a reducer agent as ascorbate would mimic enterobactin in reducing Cu+2 to Cu+1 and therefore would protect sensitive strains to  pyochelin. We observed such protection in sensitive strains.