Synergistic effect of rib80 and hit mutations on riboflavin biosynthesis and iron transport in the yeast Pichia guilliermondii

Mutant strains of the yeast Pichia guilliermondii, carrying both rib80 and hit mutations in a haploid genome, were derived from previously obtained strains with defective rib80 or hit genes, exerting negative control of the riboflavin biosynthesis and iron transport in Pichia guilliermondii. The double mutant rib80hit strains exhibited an increased level of riboflavin biosynthesis and higher activities of GTP cyclohydrolase and riboflavin synthetase. Iron deficiency caused an additional increase in riboflavin overproduction. These results suggest the synergistic interaction of the rib80 and hit mutations. A combination of both mutations in a single genome did not affect iron assimilation by the cells: ferrireductase activity, the rate of 55Fe uptake, and the iron content in cells of the double mutants remained at the level characteristic of the parent strains.