Engineering lipid droplet assembly mechanisms for improved triacylglycerol accumulation in Saccharomyces cerevisiae

Paulo Gonçalves Teixeira,Verena Siewers,Jens Nielsen,Florian David

doi:10.1093/femsyr/foy060

Paulo Gonçalves Teixeira, Verena Siewers + Show 2 more

Open Access

https://doi.org/10.1093/femsyr/foy060

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Abstract

Production of triacylglycerols (TAGs) through microbial fermentation is an emerging alternative to plant and animal-derived sources. The yeast Saccharomyces cerevisiae is a preferred organism for industrial use but has natively a very poor capacity of TAG production and storage. Here, we engineered S. cerevisiae for accumulation of high TAG levels through the use of structural and physiological factors that influence assembly and biogenesis of lipid droplets. First, human and fungal perilipin genes were expressed, increasing TAG content by up to 36% when expressing the human perilipin gene PLIN3. Secondly, expression of the FIT2 homologue YFT2 resulted in a 26% increase in TAG content. Lastly, the genes ERD1 and PMR1 were deleted in order to induce an endoplasmic reticulum stress response and stimulate lipid droplet formation, increasing TAG content by 72% for Δerd1. These new approaches were implemented in previously engineered strains that carry high flux of fatty acid biosynthesis and conversion of acyl-CoA into TAGs, resulting in improvements of up to 138% over those high-producing strains without any substantial growth effects or abnormal cell morphology. We find that these approaches not only represent a significant improvement of S. cerevisiae for TAG production, but also highlight the importance of lipid droplet dynamics for high lipid accumulation in yeast.

Highlights

Production of lipids through microbial fermentation is a progressing alternative to petroleum- and plant-derived sources
These strains provide a platform with high metabolic flux towards TAG formation, enabling us to investigate if lipid droplet (LD) assembly mechanisms can be a limiting factor in creating strains capable of accumulating even higher levels of TAG
In this work we successfully engineered yeast strains for high levels of TAG production and accumulation through targeting of processes involved in lipid droplet biogenesis and assembly

Summary

Introduction

Production of lipids through microbial fermentation is a progressing alternative to petroleum- and plant-derived sources. The technology has seen vast progress in the past few years (Zhao et al 2008; Tsigie et al 2011; Galafassi et al 2012) and production of lipids through yeast fermentation is starting to see its light as a viable industrial process. Yeasts store fatty acids in form of storage lipids, i.e. neutral lipids such as triacylglycerols (TAGs) and sterol esters (SEs) (Czabany, Athenstaedt and Daum 2007) that are accumulated intracellularly in a particular organelle known as the lipid droplet (LD). Lipid droplets have received a lot of attention the past few years and have been consistently progressing from being considered a simple fat reserve towards being recognized as an important intervenient in a variety of cellular functions and having a close relationship with many organelles such as the endoplasmic reticulum (ER), mitochondria, peroxisomes and vacuoles (Beller et al 2010; Brasaemle and Wolins 2012; Schuldiner and Bohnert 2017). Though being in recent scientific focus, the detailed mechanisms involved in the formation and budding of the LD from the ER, its cellular dynamics and the roles of associated proteins are still not completely understood (Welte 2015)

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