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GEOBACILLUS KASTOPHILUS AS A SOURCE OF THERMOSTABLE AMYLASE
Abstract
The search for new microorganisms ? sources of thermostable and thermoactive amylolytic enzymes is an important direction for the efficient processing of plant raw materials at high temperatures. A bacterial culture obtained from the thermal spring in the southeast of Iceland was used in the research. The identification of bacterial species by 16S rRNA gene sequencing has shown that the detected bacteria belong to the species Geobacillus kaustophilus. Microorganisms grown on a medium with the following composition: NaCl ? 5 g/L, peptone ? 10 g/L, yeast extract ? 5 g/L showed growth optimum at approximately 50 °C, NaCl concentration 5 g/L, and pH 7.0 within 24 hours. In order to obtain the enzyme, the bacteria were grown on a medium of the following composition: NaCl ? 5 g/L, peptone ? 1 g/L, yeast extract ? 2 g/L, indicator starch ? 15 g/L. The enzyme preparation was prepared from the culture liquid by precipitation with acetone at the ratio of 1:2 at 4 °C for 24 hours. The biocatalyst was concentrated using an ultrafiltration microcentrifugal concentrators with a MWCO of 3 kDa. The enzyme preparation showed the highest amylolytic activity of 109 U/mL determined by the formation rate of reducing sugars based on the Nelson-Somogyi method at pH 5.0 and 60 °C. The research has shown that at 70 °C the enzyme activity was 91 % of the maximum value of 37.03 U/mL as well. The study conducted using Rotational Viscometer (FungiLab) revealed a viscosity reduction of a 1.5 % non-modifying starch solution when expose to the enzyme from 11.8 to 3.2 mPa·s within 30 minutes. Therefore, research in the field of starch biotransformation and obtaining starch products, and its removal in recycling of certain types of wastepaper will move to a new level.
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