Applied Biochemistry and Biotechnology, Vol.172, No.1, 73-86, 2014
Genome Mining for New alpha-Amylase and Glucoamylase Encoding Sequences and High Level Expression of a Glucoamylase from Talaromyces stipitatus for Potential Raw Starch Hydrolysis
Mining fungal genomes for glucoamylase and alpha-amylase encoding sequences led to the selection of 23 candidates, two of which (designated TSgam-2 and NFamy-2) were advanced to testing for cooked or raw starch hydrolysis. TSgam-2 is a 66-kDa glucoamylase recombinantly produced in Pichia pastoris and originally derived for Talaromyces stipitatus. When harvested in a 20-L bioreactor at high cell density (OD600 > 200), the secreted TSgam-2 enzyme activity from P. pastoris strain GS115 reached 800 U/mL. In a 6-L working volume of a 10-L fermentation, the TSgam-2 protein yield was estimated to be similar to 8 g with a specific activity of 360 U/mg. In contrast, the highest activity of NFamy-2, a 70-kDa alpha-amylase originally derived from Neosartorya fischeri, and expressed in P. pastoris KM71 only reached 8 U/mL. Both proteins were purified and characterized in terms of pH and temperature optima, kinetic parameters, and thermostability. TSgam-2 was more thermostable than NFamy-2 with a respective half-life (t1/2) of > 300 min at 55 A degrees C and > 200 min at 40 A degrees C. The kinetic parameters for raw starch adsorption of TSgam-2 and NFamy-2 were also determined. A combination of NFamy-2 and TSgam-2 hydrolyzed cooked potato and triticale starch into glucose with yields, 71-87 %, that are competitive with commercially available alpha-amylases. In the hydrolysis of raw starch, the best hydrolysis condition was seen with a sequential addition of 40 U of a thermostable Bacillus globigii amylase (BgAmy)/g starch at 80 A degrees C for 16 h, and 40 U TSgam-2/g starch at 45 A degrees C for 24 h. The glucose released was 8.7 g/10 g of triticale starch and 7.9 g/10 g of potato starch, representing 95 and 86 % of starch degradation rate, respectively.
Keywords:Fungal genomes;Amylase;Glucoamylase;Cold starch hydrolysis;Genome mining;Triticale;Potato Starch;Pichia pastoris;Biocatalysts;Biorefinery