Optimization of the culture medium for an iron-sensitive oleaginous yeast, Rhodotorula toruloides NBRC 0559, through functional iron deficiency.

A complete iron deficiency in iron-sensitive oleaginous yeast showed insufficient biomass, resulting in a lower lipid amount, although lipid accumulation was greater compared to deficiency in other ions. In this study, the effect of functional iron deficiency on lipid production on Rhodotorula toruloides NBRC 0559 was examined. Two supplements, an iron-added (growth) supplement and an iron-free (lipid-producing) supplement were tested for detecting functional iron deficiency. The addition of iron-added supplement increased the biomass by 1.5-fold. Furthermore, the addition of iron-free supplement stimulated the growth of R. toruloides NBRC 0559 without loss of biomass (indeed, the biomass increased 1.2-fold) while also resulting in a deficiency of the iron needed for improved growth. Through iron-free supplement, the functional iron starvation effect resulted in improved lipid yield (1.7-fold) and an improved ratio of oleic acid (1.2-fold), which is considered an appropriate material for biodiesel, compared to the non-supplement-treated medium. Moreover, functional iron deficiency led to a 3.4-fold increase in the oleic acid rate compared to when all iron was completely removed from the medium. This study presents the effects and importance of iron in improving biomass and lipid production through the functional iron deficiency.