Raw starch conversion by Saccharomyces cerevisiae expressing Aspergillus tubingensis amylases
Date
2013-11
Authors
Viktor, Marko J.
Rose, Shaunita H.
Van Zyl, Willem H.
Viljoen-Bloom, Marinda
Journal Title
Journal ISSN
Volume Title
Publisher
BioMed Central
Abstract
Background: Starch is one of the most abundant organic polysaccharides available for the production of bio-ethanol as an alternative transport fuel. Cost-effective utilisation of starch requires consolidated bioprocessing (CBP) where a single microorganism can produce the enzymes required for hydrolysis of starch, and also convert the glucose monomers to ethanol.
Results: The Aspergillus tubingensis T8.4 α-amylase (amyA) and glucoamylase (glaA) genes were cloned and
expressed in the laboratory strain Saccharomyces cerevisiae Y294 and the semi-industrial strain, S. cerevisiae Mnuα1. The recombinant AmyA and GlaA displayed protein sizes of 110–150 kDa and 90 kDa, respectively, suggesting significant glycosylation in S. cerevisiae. The Mnuα1[AmyA-GlaA] and Y294[AmyA-GlaA] strains were able to utilise 20 g l⁻¹ raw corn starch as sole carbohydrate source, with ethanol titers of 9.03 and 6.67 g l⁻¹ (0.038 and 0.028 g l⁻¹ h⁻¹), respectively, after 10 days. With a substrate load of 200 g l⁻¹ raw corn starch, Mnuα1[AmyA-GlaA] yielded 70.07 g l⁻¹ ethanol (0.58 g l⁻¹ h⁻¹) after 120 h of fermentation, whereas Y294[AmyA-GlaA] was less efficient at 43.33 g l-1 ethanol (0.36 g l⁻¹ h⁻¹).
Conclusions: In a semi-industrial amylolytic S. cerevisiae strain expressing the A. tubingensis α-amylase and
glucoamylase genes, 200 g l⁻¹ raw starch was completely hydrolysed (saccharified) in 120 hours with 74%
converted to released sugars plus fermentation products and the remainder presumably to biomass. The
single-step conversion of raw starch represents significant progress towards the realisation of CBP without the need for any heat pretreatment. Furthermore, the amylases were produced and secreted by the host strain, thus circumventing the need for exogenous amylases.
Description
Publication of this article was funded by the Stellenbosch University Open Access Fund.
The original publication is available at :
Viktor, M. J., Rose, S. H., Van Zyl, W. H. & Viljoen-Bloom, M. 2013. Raw starch conversion by Saccharomyces cerevisiae expressing Aspergillus tubingensis amylases. Biotechnology for Biofuels, 6:167, doi:10.1186/1754-6834-6-167.
The original publication is available at http://www.biotechnologyforbiofuels.com/
The original publication is available at :
Viktor, M. J., Rose, S. H., Van Zyl, W. H. & Viljoen-Bloom, M. 2013. Raw starch conversion by Saccharomyces cerevisiae expressing Aspergillus tubingensis amylases. Biotechnology for Biofuels, 6:167, doi:10.1186/1754-6834-6-167.
The original publication is available at http://www.biotechnologyforbiofuels.com/
Keywords
Raw starch, Amylolytic yeast, Biofuels, Consolidated bioprocessing, Amylase, Aspergillus tubingensis
Citation
Viktor, M. J., Rose, S. H., Van Zyl, W. H. & Viljoen-Bloom, M. 2013. Raw starch conversion by Saccharomyces cerevisiae expressing Aspergillus tubingensis amylases. Biotechnology for Biofuels, 6:167, doi:10.1186/1754-6834-6-167.