Increasing n‑butanol production with saccharomyces cerevisiae by optimizing acetyl‑CoA synthesis, NADH levels and trans‑2‑enoyl‑CoA reductase expression

  • Background: n-Butanol can serve as an excellent gasoline substitute. Naturally, it is produced by some Clostridia species which, however, exhibit only limited suitability for industrial n-butanol production. The yeast Saccharomyces cerevisiae would be an ideal host due to its high robustness in fermentation processes. Nevertheless, n-butanol yields and titers obtained so far with genetically engineered yeast strains are only low. Results: In our recent work, we showed that n-butanol production via a clostridial acetoacetyl-CoA-derived pathway in engineered yeast was limited by the availability of coenzyme A (CoA) and cytosolic acetyl-CoA. Increasing their levels resulted in a strain producing up to 130 mg/L n-butanol under anaerobic conditions. Here, we show that under aerobic conditions. this strain can even produce up to 235 mg/L n-butanol probably due to a more efficient NADH re-oxidation. Nevertheless, expression of a bacterial water-forming NADH oxidase (nox) significantly reduced n-butanol production although it showed a positive effect on growth and glucose consumption. Screening for an improved version of an acetyl-CoA forming NAD+-dependent acetylating acetaldehyde dehydrogenase, adhEA267T/E568K/R577S, and its integration into n-butanol-producing strain further improved n-butanol production. Moreover, deletion of the competing NADP+-dependent acetaldehyde dehydrogenase Ald6 had a superior effect on n-butanol formation. To increase the endogenous supply of CoA, amine oxidase Fms1 was overexpressed together with pantothenate kinase coaA from Escherichia coli, and could completely compensate the beneficial effect on n-butanol synthesis of addition of pantothenate to the medium. By overexpression of each of the enzymes of n-butanol pathway in the n-butanol-producing yeast strain, it turned out that trans-2-enoyl-CoA reductase (ter) was limiting n-butanol production. Additional overexpression of ter finally resulted in a yeast strain producing n-butanol up to a titer of 0.86 g/L and a yield of 0.071 g/g glucose. Conclusions: By further optimizing substrate supply and redox power in the form of coenzyme A, acetyl-CoA and NADH, n-butanol production with engineered yeast cells could be improved to levels never reached before with S. cerevisiae via an acetoacetyl-CoA-derived pathway in synthetic medium. Moreover, our results indicate that the NAD+/NADH redox balance and the trans-2-enoyl-CoA reductase reaction seem to be bottlenecks for n-butanol production with yeast.

Download full text files

Export metadata

Metadaten
Author:Virginia Schadeweg, Eckhard Boles
URN:urn:nbn:de:hebis:30:3-423838
DOI:https://doi.org/10.1186/s13068-016-0673-0
ISSN:1754-6834
Pubmed Id:https://pubmed.ncbi.nlm.nih.gov/27924150
Parent Title (English):Biotechnology for biofuels
Publisher:BioMed Central
Place of publication:London
Document Type:Article
Language:English
Date of Publication (online):2016/12/01
Date of first Publication:2016/11/25
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2016/12/01
Tag:Acetyl-CoA; Acetylating acetaldehyde dehydrogenase; Coenzyme A; Pantothenate; Saccharomyces; Trans-2-enoyl-CoA reductase; n-Butanol
Volume:9
Issue:257
Page Number:11
First Page:1
Last Page:11
Note:
© The Author(s) 2016. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
HeBIS-PPN:425198170
Institutes:Biowissenschaften / Biowissenschaften
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 57 Biowissenschaften; Biologie / 570 Biowissenschaften; Biologie
Sammlungen:Universitätspublikationen
Open-Access-Publikationsfonds:Biowissenschaften
Licence (German):License LogoCreative Commons - Namensnennung 4.0