Boretsky Y. Genetic and biochemical mechanisms of regulation of riboflavin biosynthesis by the yeast Pichia guilliermondii

The object of research: regulation of riboflavin biosynthesis by flavinogenic yeast P. guilliermondii. The aim of research was to identify genes and to specify biochemical aspects involved in regulation of riboflavin biosynthesis by flavinogenic yeast P. guilliermondii. Methods used: microbiological, genetic, biochemical, molecular biological, mathematical and statistical. Most of the data are obtained for the first time. P. guilliermondii genes coding for ezymes of riboflavin biosynthesis and proteins involved in iron transport were identified. It was shown that regulation of riboflavin biosynthesis in P. guilliermondii occurs mainly at the transcription level of the corresponding genes. It was found that deletion of P. guilliermondii YAP1 gene leads to 2-3 fold decrease in riboflavin production under iron depletion conditions. Deletion of SEF1 gene completely blocks riboflavin overproduction under iron limiting conditions. Deletion of P. guilliermondii YFH1 gene caused oxidative stress, 2-3 folds increase in the cellular iron content and 50-70 times increased riboflavin production by the mutant strain. Damage to genes VMA1 та FRA1, both caused misregulation of ribovlavin biosynthesis and iron acquisition. In most cases oversynthesis of ribovlavin by P. guilliermondii is accompanied by misregulation of iron homeostasis and oxidative stress. A model of riboflavin biosynthesis regulation by P. guilliermondii and relative yeast species was proposed. Results of work are necessary to develop rational methods for constructions of yeast strains producing vitamin В2