Rapid production of thermostable cellulase-free xylanase by a strain of Bacillus subtilis and its properties |
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Authors: | Paula S-Pereira Alexandra Mesquita Jos C Duarte Maria Raquel Aires Barros Maria Costa-Ferreira |
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Institution: | a Department of Biotechnology, Bioprocesses and Bioengineering Unit, Instituto Nacional de Engenharia e Tecnologia Industrial, Edifício F, Estrada do Paço do Lumiar, 22, 1649–038 Lisboa, Portugal b Centre for Biological and Chemical Engineering, Instituto Superior Técnico, 1049–001 Lisboa, Portugal |
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Abstract: | A Bacillus subtilis strain isolated from a hot-spring was shown to produce xylanolytic enzymes. Their associative/synergistic effect was studied using a culture medium with oat spelts xylan as xylanase inducer. Optimal xylanase production of about 12 U ml?1 was achieved at pH 6.0 and 50°C, within 18 h fermentation. At 50°C, xylanase productivity obtained after 11 h in shake-flasks, 96,000 U l?1 h?1, and in reactor, 104,000 U l?1 h?1 was similar. Increasing temperature to 55°C a higher productivity was obtained in the batch reactor 45,000 U l?1 h?1, compared to shake-flask fermentations, 12,000 U l?1 h?1. Optimal xylanolytic activity was reached at 60°C on phosphate buffer, at pH 6.0. The xylanase is thermostable, presenting full stability at 60°C during 3 h. Further increase in the temperature caused a correspondent decrease in the residual activity. At 90°C, 20% relative activity remains after 14 min. Under optimised fermentation conditions, no cellulolytic activity was detected on the extract. Protein disulphide reducing agents, such as DTT, enhanced xylanolytic activity about 2.5-fold. When is used xylan as substrate, xylanase production decreased as function of time in contrast, with trehalose as carbon source, xylanase production in maintained constant for at least 80 h fermentation. |
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Keywords: | Fermentation Bacillus subtilis Xylanase Thermostable Trehalose |
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