Only antagonistic activity of M. pulcherrima was strictly correlated
with iron availability. In fact, the inhibitory activity as well as the diameter of the pigmented halo decreased with the increase of iron concentration in nutrient media. These results are in accordance with the findings of Sipiczki (2006) who suggested that the cells do not secrete the pigment but instead secrete a soluble,diffusible precursor that forms the pigment in the medium when it encounters iron; this observation is supported by the reduction in halo size observed when the medium is supplemented with FeCl3.