Secretory expression of β-mannanase from Bacillus circulans NT 6.7 in Lactobacillus plantarum

- The β-mannanase (Man6.7) was successfully expressed in a food grade host.
- High secretory efficiency was obtained by using the Man6.7 native signal sequence.
- The pH control cultivation was important for protein expression in L. plantarum.
- The recombinant β-mannanase showed a potential for using in MOS production.

The β-mannanase gene of Bacillus circulans NT 6.7 was successfully cloned in Lactobacillus plantarum WCFS1 using the pSIP403 expression vector and secreted to the supernatant rather than accumulated in the cells. The highest activity was achieved by controlling the pH at 6 during cultivation. Maximum mannanase activities detected in the supernatant and cell-free extract of 200 ml MRS broth were 8.2 and 0.86 U/ml, respectively. Enzyme activity in the supernatant increased to 27 U/ml by fermentation in a 5-L bioreactor with automatic pH control. The optimum temperature of recombinant β-mannanase was 50 °C and stable between 30 and 50 °C. The optimum pH was 6 with stability in the range 5-7. Enzyme activity slightly increased with Co2+ but was strongly inhibited by EDTA. The enzyme exhibited high specificity to galactomannan substrates. The main products of copra meal and locust bean gum hydrolysis were manno-oligosaccharides. Therefore, recombinant β-mannanase produced from a food grade host, L. plantarum WCFS1, showed potential for use in manno-oligosaccharides production and other food-related applications.