Optimization of the production of an extracellular and thermostable amylolytic enzyme by Thermus thermophilus HB8 and basic characterization
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The objective of this study was to determine the potential of Thermus thermophilus HB8 for accumulating a high level of extracellular, thermostable amylolytic enzyme. Initial production tests indicated clearly that only very low levels of amylolytic activity could be detected, solely from cells after extraction using the mild, non-ionic detergent Triton X-100. A sequential optimization strategy, based on statistical designs, was used to enhance greatly the production of extracellular amylolytic activity to achieve industrially attractive enzyme titers. Focus was placed on the optimal level of initial biomass concentration, culture medium composition and temperature for maximizing extracellular amylolytic enzyme accumulation. Empirical models were then developed describing the effects of the experimental parameters and their interactions on extracellular amylolytic enzyme production. Following such efforts, extracellular amylolytic enzyme accumulation was increased more than 70-fold, with enzyme titers in the 76 U/mL range. The crude extracellular enzyme was thereafter partially characterized. The optimal temperature and pH values were found to be 80 °C and 9.0, respectively. 100% of the initial enzyme activity could be recovered after incubation for 24 h at 80 °C, therefore, proving the very high thermostability of the enzyme preparation.
KeywordsThermus thermophilus HB8 Thermostable amylolytic enzyme Factorial design Central composite design Fermentation
This research was financially supported by a Canada Research Chair grant (to D. Groleau) managed by the Natural Sciences and Engineering Council of Canada (NSERC). The authors wish to thank Iulian-Zoltan Bobescu, Pisey Neang, Geneviève Fugère and Mélodie Loriaux, postdoctoral fellows and students at the University of Sherbrooke for their technical and scientific support.