Optimization of fermentation strategy for enhanced production of thermostable xylanase by recombinant Escherichia Coli

Abstract

Xylan is the second most abundant polysaccharide in plant cell wall which is hydrolyzed by the group of enzymes called hemicellulase. ß -1, 4 endo xylanase is considered as the most important among the xylanase enzymes, due to its wide industrial applications. Escherichia coli BL21 with a plasmid vector pET-22b (+) carrying xylanase coding gene, which was isolated from the extremely thermophilic bacterium called Thermotoga neapolitana, was used in the current study to enhance xylanase production. In phase 1 of this study, using the statistical approach called response surface methodology, the optimum media composition for enhanced xylanase production was successfully identified. Up to 800 IU mL-1 xylanase activity was observed in optimized media, which is around 3 folds higher compared to the activity achieved in unoptimized medium. In phase 2, optimization of lactose-based induction strategy was carried out to enhance the xylanase production. As a result of this induction optimization, the intracellular xylanase production was enhanced up to 2600 IU mL-1. In phase 3, as a part of process scale up, the study was focused on developing suitable fed-batch fermentation conditions, by optimizing nutrients and inducer feeding strategy. With the optimized fed batch fermentation conditions in 16 L stirred tank bioreactor, the xylanase activity was enhanced up to 11000 IU mL-1, which is 4 to 5 folds higher compared to activity reported in previous studies. During physicochemical characterization in phase 4 of the current study, the optimum temperature and pH of xylanse enzyme was found to be 80°C and 6.5, respectively. Among the metal ions and chelating agents tested, zinc sulfate and ethylenediaminetetraacetic acid were found to have the highest inhibitory effect on xylanase enzyme in this study.