Hydroxamate siderophore synthesis by Phialocephala fortinii, a typical dark septate fungal root endophyte

The siderophore production of various isolates of Phialocephala fortinii wa s assessed quantitatively as well as qualitatively in batch assays under pu re culture conditions at different pH values and iron(III) concentrations. We found a distinct effect of both of these parameters on siderophore synth esis and as well as on fungal growth. In comparative analyses of two of the isolates, maximum siderophore production was found at a pH in the range of pH 4.0 to 4.5 while, under the experimental conditions employed, the optim al concentration of ferric iron was determined to be between 20-40 mug iron (III) l(-1) (0.36-0.72 muM, respectively). HPLC analysis of the culture fi ltrate of most of the isolates of P. fortinii revealed the excretion of fer ricrocin as main hydroxamate siderophore, followed by ferrirubin and ferric hrome C. The pattern of release of these three substances proved to be depe ndent on pH and iron(III) concentration of the culture medium, and to be sp ecific for each isolate under investigation.