TITLE:
Nitrogen Source Affects Glycolipid Production and Lipid Accumulation in the Phytopathogen Fungus Ustilago maydis
AUTHORS:
Ariana Zavala-Moreno, Roberto Arreguin-Espinosa, Juan Pablo Pardo, Lucero Romero-Aguilar, Guadalupe Guerra-Sánchez
KEYWORDS:
Nitrogen Starvation, Yeast Glycolipids, Lipid Droplets, Lipid Accumulation
JOURNAL NAME:
Advances in Microbiology,
Vol.4 No.13,
October
21,
2014
ABSTRACT: When cultured in
medium limited of nitrogen sources, the phytopathogen Ustilago maydis produces two amphipathic glycolipids: Ustilagic
acid (UA) and Mannosylerythritol lipid (MEL), which in addition to the hydrophilic
moiety, contain dior tri-hydroxylated C16 fatty acids (UA), or C8 and C16 saturated fatty acids (MEL). We compared the growth and
morphology of cells in YPD and in minimum media containing glucose and nitrogen
sources such as nitrate or urea and those deprived of nitrogen.
Nitrogen-starved cells showed a dramatic accumulation of internal lipids
identified as lipid droplets when stained with the hydrophobic probe BODIPY;
these lipid droplets were enriched in unsaturated fatty acids. Fatty acids in
YPD or medium containing nitrate as nitrogen source showed a combination of
saturated/unsaturated lipids, but when urea was the nitrogen source, cells only
contained saturated fatty acids. The glycolipid profiles produced in the presence
or absence of nitrogen showed preferences towards the production of one kind of
glycolipid: cells in media containing nitrate or urea produced different
proportions of UA/MEL, but under nitrogen starvation cells contained only UA.
The emulsification capacity of the glycolipids produced in media with or
without nitrogen was similar (72% - 76%). HPLC of the glycolipids allowed the
separation of fractions with different emulsifying characteristics. Our results
indicate that U. maydis accumulates
lipid droplets when deprived of nitrogen source and confirm that UA is not
under nitrogen control, but rather that MEL and lipid droplets are produced and
oppositely regulated by nitrogen.