D. Fedorovich et al., Iron uptake by the yeast Pichia guilliermondii. Flavinogenesis and reductive iron assimilation are co-regulated processes, BIOMETALS, 12(4), 1999, pp. 295-300
Pichia guilliermondii cells overproduce riboflavin (vitamin B2) in responce
to iron deprivation. The increase in ferrireductase activity in iron-starv
ed P. guilliermondii cells correlated with the increase in flavin excretion
. As in Saccharomyces cerevisiae, a typical b-type cytochrome spectrum was
associated with the plasma membrane fraction of P. guillermondii and the ce
ll ferrireductase activity was strongly inhibited by diphenylene-iodonium,
an inhibitor of flavoproteins, in both yeasts. Mutants of P. guilliermondii
with increased ferrireductase activity were selected for further investiga
tion of the relationship between iron reduction/uptake and flavin productio
n. The obtained mutation has been called hit (high iron transport). A hit m
utant with a single recessive mutation showed the following phenotype: high
ferrireductase activity, increased rate of iron uptake and elevated flavin
ogenic activity. Cu(II) (50 mu m) strongly inhibited the growth of the hit
mutant compared to the wild-type. The mutant cells grown in copper-suppleme
nted medium (5-25 mu m) showed an increase of the ferrireductase activity (
up to 2-3 fold). The copper content of the mutant cells grown under these c
onditions was also higher (1.5-2 fold) than that of the wild-type. The role
of the HIT gene of P. guillermondii in the regulation of iron, copper and
flavin metabolisms is discussed.