Process Development for Concentration and Stabilization of Recombinant Endoxylanase Expressed in Bacillus subtilis

A strong constitutive $P_{JH}$ promoter from Bacillus sp. was applied to overexpress the endoxylanase gene in Bacillus subtilis. The expression plasmid, pJHKJ4, was designed to contain the $P_{JH}$ promoter and open reading frame of endoxylanase including its own promoter. The plasmid was introduced into B. subtilis DB431 and the resulting transformant was grown on LB glucose medium. The endoxylanase activity in the culture supernatant reached about 140 unit/ml. The enzyme in the supernatant was efficiently concentrated to 70% by two-step treatments of ammonium sulfate saturation and ultrafiltration. The stabilization of concentrated enzyme solution at different storage temperatures was examined with various stabilizers such as NaCl, $CaCl_2$, sucrose, sorbitol, polyethylene glycol, and Tween-80.