Metabolic Flexibility of Yarrowia lipolytica Growing on Glycerol.

Michael Egermeier,Hannes Russmayer,Hans Marx,Michael Sauer,Michael Sauer

doi:10.3389/fmicb.2017.00049

Abstract

The yeast Yarrowia lipolytica is a fascinating microorganism with an amazing metabolic flexibility. This yeast grows very well on a wide variety of carbon sources from alkanes over lipids, to sugars and glycerol. Y. lipolytica accumulates a wide array of industrially relevant metabolites. It is very tolerant to many environmental factors, above all the pH value. It grows perfectly well over a wide pH range, but it has been described, that the pH has a decisive influence on the metabolite pattern accumulated by this yeast. Here, we set out to characterize the metabolism of different Y. lipolytica strains, isolated from various environments, growing on glycerol at different pH values. The conditions applied for strain characterization are of utmost importance. Shake flask cultures lead to very different results, when compared to controlled conditions in bioreactors regarding pH and aeration. Only one of the tested strains was able to accumulate high amounts of citric acid in shake flask experiments, whereas a group of six strains turned out to accumulate citric acid efficiently under controlled conditions. The present study shows that strains isolated from dairy products predominantly accumulate sugar alcohols at any given pH, when grown on glycerol under nitrogen-limitation.

Highlights

The yeast Yarrowia lipolytica has been studied and investigated for biotechnological applications since the 1960s, when high yield citric acid production in Y. lipolytica reached about twice the yield obtained in Aspergillus niger (Kurtzman, 2011)
Strains of Y. lipolytica cultivated in shake flasks on defined YNB medium with 5% pure glycerol grew very slowly and did not exceed 6.8 g∗L−1 of dry biomass after 200 h of cultivation (Table S1)
Citric acid was preferably formed at pH values higher than 4.5, with an optimum around pH 5.5 and reached conversion yields of >0.4 g∗g−1 (Table 2)

Summary

Introduction

The yeast Yarrowia lipolytica has been studied and investigated for biotechnological applications since the 1960s, when high yield citric acid production in Y. lipolytica reached about twice the yield obtained in Aspergillus niger (Kurtzman, 2011). Scientific focus concentrated on the production of metabolites (Coelho et al, 2010; Barth, 2013), and on lipid production for biofuel applications (Beopoulos et al, 2008, 2009; Tai and Stephanopoulos, 2013; Rakicka et al, 2015), the production and secretion of heterologous proteins (Nicaud et al, 2002) and on the genetic mechanisms of the dimorphic growth in yeast (Herrero et al, 1999; Ruiz-Herrera and Sentandreu, 2002). There are three primary lab strains, including the current type-strain NRRL YB-423 (CBS 6124) which has been isolated in 1945 from a maize-processing plant (USA) and later on examined for the secretion of lipases. The third important lab-strain was isolated from soil in Germany (H 222) and used for the production of organic acids (Otto et al, 2013)

Objectives

Methods

Results

Conclusion