Isolation, characterization, and application of thermotolerant Streptomyces sp. K5 for efficient conversion of cellobiose to chitinase using pulse- feeding strategy

Abstract

In this study, the selection of target sugars in lignocellulosic hydrolysate and the implementation of a bioprocess strategy led to efficient production of a catalyst for chitinous bioresource conversion. Streptomyces sp. K5, a chitinase producer in the presence of glucose, was isolated at 50 °C on an agar plate with glucose and colloidal chitin. The K5 was found to produce chitinase with a maximum activity of 70 U/L in a medium containing glucose and xylose as well as colloidal chitin as an inducer. The assimilation of glucose and xylose, however, was extremely slow, with significant residual being present even after 168 h of incubation. Assimilation tests of glucose, xylose, and cellobiose confirmed that K5 produces chitinase without chitinous inducer and assimilates cellobiose much more rapidly than either glucose or xylose. At the same time, the complete exhaustion of each sugar initiated chitinase inactivation. A pulse- feeding strategy was adopted for the cellobiose, taking its rapid assimilation, β-glucosidase activity, and chitinase inactivation into account, and a maximum chitinase activity of 235 U/L was achieved under pulse- feeding conditions that included four pulses.