To produce lactulose efficiently, the gene encoding cellobiose 2-epimerase (CE) from Dictyoglomus sp. NZ13-RE01 was cloned into pET-28a, resulting the plasmid pET-28a-NZ13 and expressed in E. coli BL21(DE3). The activity of recombinant NZ13-CE was 0.53 U/mL after 24 h induction with IPTG in shaking flask, and the highest enzyme activity of 4.3 U/mL was obtained with high cell density cultivation in 7.5 L fermenter. NZ13-CE was purified by nickel ion affinity chromatography and biochemically characterized. The molecular mass of NZ13-CE was 45.5 kDa, the optimal temperature and pH were 80 ℃ and 8.0, respectively. The activity half-time of NZ13-CE was 181.5 min at 80 ℃, and the highest conversion rate from lactose to lactulose was 52.5%. In addition, the final ratio of epilactose only was 9%. The heterologous expression of NZ13-CE in E. coli provided a great potential for the production of lactulose.
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