Oleaginicity of the yeast strain Saccharomyces cerevisiae D5A

Qiaoning He,Bryon S. Donohoe,Michael E. Himmel,Eric P. Knoshaug,Min Zhang,Shihui Yang,Stefanie Van Wychen,Yongfu Yang

doi:10.1186/s13068-018-1256-z

Qiaoning He, Bryon S. Donohoe + Show 6 more

Open Access

https://doi.org/10.1186/s13068-018-1256-z

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Abstract

BackgroundThe model yeast, Saccharomyces cerevisiae, is not known to be oleaginous. However, an industrial wild-type strain, D5A, was shown to accumulate over 20% storage lipids from glucose when growth is nitrogen-limited compared to no more than 7% lipid accumulation without nitrogen stress.Methods and resultsTo elucidate the mechanisms of S. cerevisiae D5A oleaginicity, we compared physiological and metabolic changes; as well as the transcriptional profiles of the oleaginous industrial strain, D5A, and a non-oleaginous laboratory strain, BY4741, under normal and nitrogen-limited conditions using analytic techniques and next-generation sequencing-based RNA-Seq transcriptomics. Transcriptional levels for genes associated with fatty acid biosynthesis, nitrogen metabolism, amino acid catabolism, as well as the pentose phosphate pathway and ethanol oxidation in central carbon (C) metabolism, were up-regulated in D5A during nitrogen deprivation. Despite increased carbon flux to lipids, most gene-encoding enzymes involved in triacylglycerol (TAG) assembly were expressed at similar levels regardless of the varying nitrogen concentrations in the growth media and strain backgrounds. Phospholipid turnover also contributed to TAG accumulation through increased precursor production with the down-regulation of subsequent phospholipid synthesis steps. Our results also demonstrated that nitrogen assimilation via the glutamate–glutamine pathway and amino acid metabolism, as well as the fluxes of carbon and reductants from central C metabolism, are integral to the general oleaginicity of D5A, which resulted in the enhanced lipid storage during nitrogen deprivation.ConclusionThis work demonstrated the disequilibrium and rebalance of carbon and nitrogen contribution to the accumulation of lipids in the oleaginous yeast S. cerevisiae D5A. Rather than TAG assembly from acyl groups, the major switches for the enhanced lipid accumulation of D5A (i.e., fatty acid biosynthesis) are the increases of cytosolic pools of acetyl-CoA and NADPH, as well as alternative nitrogen assimilation.

Highlights

The model yeast, Saccharomyces cerevisiae, is not known to be oleaginous
Lipid and metabolite contents differed markedly between S. cerevisiae D5A and BY4741 We previously discovered that S. cerevisiae strain D5A is naturally oleaginous compared to other industrially relevant strains [37]
A transcriptomic study to determine the underlying mechanisms in D5A compared to the laboratory haploid strain of BY4741 was carried out in this work

Summary

Introduction

The model yeast, Saccharomyces cerevisiae, is not known to be oleaginous. an industrial wildtype strain, D5A, was shown to accumulate over 20% storage lipids from glucose when growth is nitrogen-limited compared to no more than 7% lipid accumulation without nitrogen stress. Lipid-based biofuels produced from microorganisms are attractive substitutes for fossil fuels due to their sustainable and secure supply [1]. These microorganisms can be grown on a variety of lignocellulosic carbon sources negating the need for large agricultural areas of dedicated oil crops [2]. Studies of oleaginous microorganisms, such as microalgae, yeasts, filamentous fungi, and bacteria, have revealed that de novo lipid metabolism is dependent on environmental conditions, nutrient shortages with an excess of carbohydrates [1, 9,10,11], while ex novo biosynthesis is not [8]. Among the potential limiting nutrients, nitrogen limitation has emerged as a reliable and efficient strategy to promote lipid production

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Conclusion