FERRIC TRON REDUCTION BY CRYPTOCOCCUS-NEOFORMANS

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).