Modulation of Lipid Body Size and Protein Profiles in the Oleaginous Fungus by Changing Nitrogen Concentration in Culture Medium

Abstract

Mortierella ramanniana var. angulispora,an oleaginous fungus, accumulates large amounts of triacylglycerol (TG) and lipid bodies [1,2]. Lipid bodies in this fungus have a diameter of about 1 dun at the initial culture phase and then enlarge into a diameter of about 2–3 μm during lipid accumulation [2]. To form matured lipid bodies, TG and/or its precursors have to transport to lipid bodies. We have characterized the lipid transport into lipid bodies using fluorescent phospholipid analogues to find several transport pathways for the lipid body formation [2,3]. The question arises how the lipid transport into lipid bodies is regulated. To address the question, we looked for culture conditions to change the size of lipid bodies and characterized the protein profile of lipid bodies with different size. We found that changing nitrogen concentration represented as carbon to nitrogen ratio (C/N ratio) in culture medium affected the lipid body size in addition to lipid content. Comparing the lipid body fraction obtained from fungal cells with different lipid body size revealed that tyrosine phosphorylation was enhanced in the lipid body fraction when fungal cells were cultured with a lower C/N ratio (higher concentration of nitrogen).