Research Articles (Microbiology)

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Browsing Research Articles (Microbiology) by Subject "Amylase"

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    Different genetic backgrounds influence the secretory expression of the LKA1-encoded Lipomyces kononenkoae alpha-amylase in industrial strains of Saccharomyces cerevisiae
    (Kluwer (now part of Springer), 2002-01) Gundllapalli Moses, S. B.; Cordero Otero, R. R.; La Grange, Daniel C.; Van Rensburg, Pierre; Pretorius, Isak S.
    A haploid laboratory strain and four industrial (baking, brewing, wine, ATCC) strains of Saccharomyces cerevisiae were transformed with the Lipomyces kononenkoae alpha-amylase-encoding gene (LKA1). These transformants displayed significant differences in terms of the level of secretory expression of LKA1 under control of the PGK1 promoter and terminator, as well as their ability to produce and secrete the LKA1-encoded rawstarch-degrading alpha-amylase and to ferment starch. These results demonstrate the importance of the selection of appropriate host strains for yeast development pursuant to starch conversion into commercially important commodities via consolidated bioprocessing.
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    Raw starch conversion by Saccharomyces cerevisiae expressing Aspergillus tubingensis amylases
    (BioMed Central, 2013-11) Viktor, Marko J.; Rose, Shaunita H.; Van Zyl, Willem H.; Viljoen-Bloom, Marinda
    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.