Heterologous production of polyunsaturated fatty acids in Saccharomyces cerevisiae causes a global transcriptional response resulting in reduced proteasomal activity and increased oxidative stress

Abstract

Due to their health benefits there is much interest in developing microbial processes for efficient production of polyunsaturated fatty acids (PUFAs). In this study we co-expressed Mucor rouxii Δ(12) - and Δ(6) -desaturase genes in Saccharomyces cerevisiae, which resulted in a yeast strain that accumulated linoleic acid and γ-linolenic acid in the different lipid species. Additionally, the strain contained higher levels of phospholipids and lower levels of ergosterol than the reference strain. Integrated analysis of the transcriptome revealed decreased expression of genes involved in ergosterol biosynthesis, but more unexpectedly it also pointed towards attenuated activity of the ubiquitin-proteasome system and a reduced oxidative stress response. In vitro and in vivo measurements showed reduced levels of all three proteasomal activities and also increased levels of reactive oxidative species in the PUFA-producing strain. Overall our results clearly show that PUFAs in yeast can be detrimental for several key cellular pathways, such as the oxidative stress response and proteasomal activity, suggesting that the membrane composition is of vital importance for these processes.

Transcriptional and antioxidative responses to endogenous polyunsaturated fatty acid accumulation in yeast

“…Although PUFA accumulation in yeast induces endogenous oxidative stress via the increased levels of ROS [32,44], we did not observe any changes in the antioxidant transcript steady state levels. However, some general stress response genes were up-regulated such as HSP26, HSP78, HSP12, HSP150, SSE2, and YGP1.…”

“…However, this phenomenon should be further investigated in more detail. In addition, PUFA accumulation was previously reported to lead to down-regulation of GTT2 gene transcripts in PUFA-producing yeast [44].…”

Understanding biocatalyst inhibition by carboxylic acids

“…Further tests in S. cerevisiae have confirmed not only increased production of reactive oxygen species in these conditions (Teixeira et al, 2004; Cipak et al, 2008; Ruenwai et al, 2011), but also increased activity of ROS-scavenging catalase and superoxide dismutase enzymes (Teixeira et al, 2004; Cipak et al, 2008). This increased abundance of ROS in yeast has largely been attributed to damage of the cell membrane and/or damage to the mitochondrial membrane (Mollapour et al, 2008; King et al, 2010; Lennen et al, 2011; Ruenwai et al, 2011). Damage to the mitochondrial membrane not only results in decreased function of the mitochondrial respiratory chain, but can also result in mutagenesis of the vulnerable mitochondrial DNA (Piper, 1999).…”

“…Many transcriptome-based studies have noted activation of oxidative stress response genes during production of or challenge with various carboxylic acids (King et al, 2010; Legras et al, 2010; Lennen et al, 2011; Ruenwai et al, 2011). Further tests in S. cerevisiae have confirmed not only increased production of reactive oxygen species in these conditions (Teixeira et al, 2004; Cipak et al, 2008; Ruenwai et al, 2011), but also increased activity of ROS-scavenging catalase and superoxide dismutase enzymes (Teixeira et al, 2004; Cipak et al, 2008).…”

Editorial: Industrial systems biology

“…sight into the metabolism of this organism [8] as well as the engineering of yeast for the production of poly-unsaturated fatty acids [9] is included in this special issue.…”