Characterization of hydroxamate siderophores and siderophore-mediated iron uptake in Gaeumannomyces graminis var. tritici

Abstract

Under iron-deficient conditions, Gaeumannomyces graminis var. tritici ( Ggt) produces dimerum acid and coprogen B as well as traces of two other unidentified hydroxamate siderophores. The production of coprogen B decreased and of dimerum acid increased with the rise in pH of the growth medium. While iron concentration of 3 μ m completely repressed siderophore secretion, a low iron concentration (0·06 μ m) was necessary for maximal production. Siderophore-mediated iron uptake for dimerum acid and coprogen B exhibited active transport and was optimum at pH 4·5–5 and 30 °C. Michaelis kinetics with apparent K m s of 6·8 and 11 μ m, and V max of 0·26 and 0·54 nmoles mg −1 min −1 was obtained for dimerum acid and coprogen B, respectively. While Ggt could utilize iron effectively from siderophores produced by other fungi, utilization of iron from pseudobactin, ferrioxamine B, EDTA and EDDHA was ineffective. Competition studies between dimerum acid and various siderophores suggest a common transport system with coprogen B, rhodotorulic acid and ferrichrome but not with fusigen and triacetylfusigen. Wheat seedlings were capable of utilizing iron efficiently from dimerum acid and coprogen B. The possible influence of the pathogen's siderophores on its survival and virulence is discussed.