Comparison of Nitrogen Depletion and Repletion on Lipid Production in Yeast and Fungal Species

Shihui Yang,Stefanie Van Wychen,Min Zhang,Wei Wang,Hui Wei,Philip Pienkos,Michael Himmel

doi:10.3390/en9090685

Abstract

Although it is well known that low nitrogen stimulates lipid accumulation, especially for algae and some oleaginous yeast, few studies have been conducted in fungal species, especially on the impact of different nitrogen deficiency strategies. In this study, we use two promising consolidated bioprocessing (CBP) candidates to examine the impact of two nitrogen deficiency strategies on lipid production, which are the extensively investigated oleaginous yeast Yarrowia lipolytica, and the commercial cellulase producer Trichoderma reesei. We first utilized bioinformatics approaches to reconstruct the fatty acid metabolic pathway and demonstrated the presence of a triacylglycerol (TAG) biosynthesis pathway in Trichoderma reesei. We then examined the lipid production of Trichoderma reesei and Y. lipomyces in different media using two nitrogen deficiency strategies of nitrogen natural repletion and nitrogen depletion through centrifugation. Our results demonstrated that nitrogen depletion was better than nitrogen repletion with about 30% lipid increase for Trichoderma reesei and Y. lipomyces, and could be an option to improve lipid production in both oleaginous yeast and filamentous fungal species. The resulting distinctive lipid composition profiles indicated that the impacts of nitrogen depletion on yeast were different from those for fungal species. Under three types of C/N ratio conditions, C16 and C18 fatty acids were the predominant forms of lipids for both Trichoderma reesei and Y. lipolytica. While the overall fatty acid methyl ester (FAME) profiles of Trichoderma reesei were similar, the overall FAME profiles of Y. lipolytica observed a shift. The fatty acid metabolic pathway reconstructed in this work supports previous reports of lipid production in T. reesei, and provides a pathway for future omics studies and metabolic engineering efforts. Further investigation to identify the genetic targets responsible for the effect of nitrogen depletion on lipid production improvement will facilitate strain engineering to boost lipid production under more optimal conditions for productivity than those required for nitrogen depletion.

Highlights

Bacteria, yeast, and fungi can naturally synthesize fatty acids, isoprenoids, or polyalkanoates for energy storage
Even though engineering the TAG biosynthesis pathway has been the focus of Y. lipolytica
The same approach was used in this study to biosynthesis pathways in Trichoderma reesei [62]

Summary

Introduction

Yeast, and fungi can naturally synthesize fatty acids, isoprenoids, or polyalkanoates for energy storage. These compounds have high energy densities and are compatible with current fuel infrastructure, permitting their exploitation for hydrocarbon fuel production [1,2,3,4]. Energies 2016, 9, 685 bioprocessing (CBP) is a promising strategy for economical lignocellulosic biofuel production, which biologically integrates enzyme production, saccharification, and fermentation. Two strategies have been utilized for CBP strain development, which are called “native” and “recombinant” strategies. A native strategy increases the fuel productivity of a naturally cellulolytic microorganism, whereas a recombinant strategy enables a microbe with excellent productivity with monomeric sugars to utilize lignocellulosic biomass directly [5,6].

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