Engineering yeasts for raw starch conversion
Abstract
Next to cellulose, starch is the most abundant hexose polymer in plants, an import food and feed source and a preferred substrate for the production of many industrial products. Efficient starch hydrolysis requires the activities of both α-1,4 and α-1,6-debranching hydrolases, such as endo-amylases, exo-amylases, debranching enzymes, and transferases. Although amylases are widely distributed in nature, only about 10 % of amylolytic enzymes are able to hydrolyse raw or unmodified starch, with a combination of α-amylases and glucoamylases as minimum requirement for the complete hydrolysis of raw starch. The cost-effective conversion of raw starch for the production of biofuels and other important by-products requires the expression of starch-hydrolysing enzymes in a fermenting yeast strain to achieve liquefaction, hydrolysis, and fermentation (Consolidated Bioprocessing, CBP) by a single organism. The status of engineering amylolytic activities into Saccharomyces cerevisiae as fermentative host is highlighted and progress as well as challenges towards a true CBP organism for raw starch is discussed. Conversion of raw starch by yeast secreting or displaying α-amylases and glucoamylases on their surface has been demonstrated, although not at high starch loading or conversion rates that will be economically viable on industrial scale. Once efficient conversion of raw starch can be demonstrated at commercial level, engineering of yeast to utilize alternative substrates and produce alternative chemicals as part of a sustainable biorefinery can be pursued to ensure the rightful place of starch converting yeasts in the envisaged bio-economy of the future.
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Starch enzymatic hydrolysis is complex and requires the activity of several enzymes, such as α-amylase, isoamylase, pullulanase, β-amylase, and glucoamylase.
“Starch enzymatic hydrolysis is complex and requires the activity of several enzymes, such as α-amylase, isoamylase, pullulanase, β-amylase, and glucoamylase.”
From The Enzymatic Conversion of Major Algal and Cyanobacterial Carbohydrates to Bioethanol (2016) · cites this paper as Van Zyl et al., 2012
Endo-acting α-amylases hydrolyze amylose and amylopectin α-(1→4) glycosidic bonds randomly, producing glucose, maltose, and maltodextrins of 10-20 glucose units.
“The endo-acting α-amylases (EC 3.2.1.1)hydrolyze amylose and amylopectin α-(1→4) glycosidic bonds randomly, producing glucose, maltose (two glucose residues), and maltodextrins of 10-20 glucose units.”
From The Enzymatic Conversion of Major Algal and Cyanobacterial Carbohydrates to Bioethanol (2016) · cites this paper as Van Zyl et al., 2012
Exo-acting β-amylases hydrolyze amylose from the non-reducing ends to produce predominantly maltose, which is cleaved into two glucose residues by glucoamylases.
“The exo-acting β-amylases (EC 3.2.1.2) hydrolyze amylose from the non-reducing ends to produce predominantly maltose, which is cleaved into two glucose residues by glucoamylases (EC 3.2.1.3)(Figure 2A) [reviewed by Van Zyl et al. (2012)].”
From The Enzymatic Conversion of Major Algal and Cyanobacterial Carbohydrates to Bioethanol (2016) · cites this paper as Van Zyl et al., 2012
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References 149 · Cited by 107
- Authors
- van Zyl, W. H., Bloom, M., & Viktor, M. J.
- Affiliations
- Stellenbosch University (ZA)
- Venue
- Applied Microbiology and Biotechnology
- Published
- 2012-07-14
- Volume
- 95
- Issue
- 6
- Pages
- 1377-1388
- ISSN
- 0175-7598 (ISSN-L)
- 1432-0614
- OpenAlex
- W2151160051
- Cited by
- 107
- References
- 149
- Citations by year
- 2026: 3 · 2025: 8 · 2024: 2 · 2023: 9 · 2022: 9 · 2021: 13 · 2020: 7 · 2019: 6 · 2018: 5 · 2017: 10 · 2016: 10 · 2015: 11 · 2014: 6 · 2013: 6 · 2012: 1
- FWCI
- 0.67
- Type
- journal article
- Language
- en
- Open access
- closed
- Licence
- www.springer.com/tdm (tdm)
- Locations
- Applied Microbiology and Biotechnology (publishedVersion)
- PubMed (publishedVersion)
- SUNScholar (Stellenbosch University) (submittedVersion)
- Topics
- Physical Sciences › Engineering › Biomedical Engineering › Biofuel production and bioconversion
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Biotechnology › Enzyme Production and Characterization
- Life Sciences › Biochemistry, Genetics and Molecular Biology › Molecular Biology › Microbial Metabolic Engineering and Bioproduction
- Keywords
- consolidated bioprocessing, amylolytic enzymes, alpha-amylase, glucoamylase, debranching enzyme, starch hydrolysis, Saccharomyces cerevisiae, yeast engineering, enzyme display, biofuels, biorefinery, bioeconomy
- MeSH terms
- Fermentation, Saccharomyces cerevisiae, Starch, Saccharomyces cerevisiae Proteins, Metabolic Engineering
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