Nitrogen Source Affects Glycolipid Production and Lipid Accumulation in the Phytopathogen Fungus &amp;lt;i&amp;gt;Ustilago maydis&amp;lt;/i&amp;gt;

Ariana Zavala-Moreno,Roberto Arreguin-Espinosa,Lucero Romero-Aguilar,Guadalupe Guerra-Sánchez,Juan Pablo Pardo

doi:10.4236/aim.2014.413104

Nitrogen Source Affects Glycolipid Production and Lipid Accumulation in the Phytopathogen Fungus &lt;i&gt;Ustilago maydis&lt;/i&gt;

Ariana Zavala-Moreno, Roberto Arreguin-Espinosa + Show 3 more

Open Access

https://doi.org/10.4236/aim.2014.413104

Copy DOI

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.

Highlights

The yeast of Ustilago maydis produces extracellular glycolipids with surfactant activity that enhance the availability of hydrophobic nutrients during its interaction with the host [1] [2]
We studied the growth and morphology of U. maydis yeasts cultured in YPD and minimal media (MM) containing glucose as carbon source without a nitrogen source (MM−N), or glucose under nitrogen limiting conditions using nitrate (MM+N) or Urea (MM+U) as nitrogen sources
In the case of Minimum media with urea (MM+U), the exponential growth rate was dilatory smaller than the rates found for the other culture conditions, and this was associated with a low yield as well as the stationary stage

Summary

Introduction

The yeast of Ustilago maydis produces extracellular glycolipids with surfactant activity that enhance the availability of hydrophobic nutrients during its interaction with the host [1] [2] These biosurfactants are derivatives of two classes of amphiphatic glycolipids: Ustilagic acid (UA) and Mannosylerythritol lipids (MEL). Mannosylerythritol lipids (MEL) are secreted in at least four different varieties (ABCD), depending on the number of acetyl groups attached to the disaccharide [3]-[11] and a glycosyltransferase is essential for the biosynthesis of MEL; expression of this enzyme is strongly induced by limitations on nitrogen availability [11] To produce these glycolipids, U. maydis requires raw materials to synthesize the lipid and carbohydrate moieties. This study confirmed that in contrast to MEL, UA is not under nitrogen control, and that U. maydis is a potential microorganism for the production of lipids for biofuels and biosurfactants in nitrogen deprived conditions

Objectives

Results

Conclusion