The pathogenic yeast Cryptococcus neoformans must reduce Fe(III) to Fe
(II) prior to uptake. We investigated mechanisms of reduction using th
e chromogenic ferrous chelator bathophenanthroline disulfonate, Iron-d
epleted cells reduced 57 nmol of Fe(III) per 10(6) cells per h, while
iron-replete cells reduced only 8 nmol of Fe(III). Exponential-phase c
ells reduced the most and stationary-phase cells reduced the least Fe(
III), independent of iron status. Supernatants from iron-depleted cell
s reduced up to 2 nmol of Fe(III) per 10(6) cells per h, while superna
tants from iron-replete cells reduced 0.5 nmol of Fe(III), implying re
gulation of the secreted reductant(s). One such reductant is 3-hydroxy
anthranilic acid (3HAA), which was found at concentrations up to 29 mu
M in iron-depleted cultures but <2 mu M in cultures supplemented with
iron, Moreover, when washed and resuspended in low iron medium, iron-
depleted cells secreted 20.4 mu M 3HAA, while iron-replete cells secre
ted only 4.5 mu M 3HAA. Each mole of 3HAA reduced 3 mol of Fe(III), an
d increasing 3HAA concentrations correlated with increasing reducing a
ctivity of supernatants; however, 3HAA. accounted for only half of the
supernatant's reducing activity, indicating the presence of additiona
l reductants. Finally, we found that melanized stationary-phase cells
reduced 2 nmol of Fe(III) per 10(6) cells per h-16 times the rate of n
onmelanized cells-suggesting that this redox polymer participates in r
eduction of Fe(III).