Influence of Nitrogen Metabolism on Lipid Accumulation by Rhodosporidium toruloides CBS 14

Abstract

Rhodosporidium toruloides CBS 14 was grown in batch culture with urea as principal nitrogen source. The lipid content increased from 18% (w/w) with NH+ 4-grown cells to 52% (w/w) after 90 h growth. Urea was rapidly taken up and catabolized to release intracellular NH+ 4, which accumulated between 10 and 30 h growth. The increase in pool NH+ 4 content was mirrored by an increase in citric acid accumulation and excretion from the cells. The production of intracellular NH+ 4, sufficient to permit lipid accumulation, could be attributed to the increase in activity of urease over this period. Similarly, other catabolic enzymes, such as arginase, threonine dehydratase and NAD+: glutamate dehydrogenase, were also induced (or derepressed) when the respective amino acids were used as medium nitrogen source. Growth with mixed organic and inorganic nitrogen compounds considerably decreased the lipid content and was accompanied by a reduction in activity of the various catabolic enzymes concerned. The significance of nitrogen catabolism during lipid accumulation in this yeast is discussed.