Adsorption-based immobilization of Caldicellulosiruptor saccharolyticus cellobiose 2-epimerase on Bacillus subtilis spores.

Nonrecombinant spore was examined as a novel immobilization support to adsorb enzymes. Caldicellulosiruptor saccharolyticus cellobiose 2-epimerase (CsCE), efficiently producing lactulose using lactose as a single substrate, was immobilized on Bacillus subtilis spores via adsorption. The immobilization process was optimized, and the properties of immobilized CsCE and the interactions between the enzyme and spores were also investigated. Under the optimized conditions (pH 4.5, temperature 4 °C, reaction time 2 H, and initial enzyme concentration 2.4 mg/mL), the maximum adsorbed amount of CsCE was 1.47 mg/10(11) spores, and the enzyme activity recovery was 79.4%. The spore-immobilized CsCE presented a higher pH and thermal stability than a free enzyme. Total desorption of the immobilized enzyme was only achieved by treatment with 1.0 M NaCl at pH 1.0, indicating a strong adsorption between CsCE and B. subtilis spores. Efficient binding may require a potent combination of electrostatic and hydrophobic interactions between spores and an enzyme. The immobilized CsCE was applied to produce 395 g/L lactulose after 4 H. Moreover, the spores could be regenerated and the spore-immobilized enzyme showed good reusability as it retained approximately 70% of its initial activity after eight recycles.