Characterization and high-efficiency secreted expression in Bacillus subtilis of a thermo-alkaline ?-mannanase from an alkaliphilic Bacillus clausii strain S10.

ABSTRACT: BACKGROUND:?-Mannanase catalyzes the cleavage of ?-1,4-linked internal linkages of mannan backbone randomly to produce new chain ends. Alkaline and thermostable ?-mannanases provide obvious advantages for many applications in biobleaching of pulp and paper, detergent industry, oil grilling operation and enzymatic production of mannooligosaccharides. However, only a few of them are commercially exploited as wild or recombinant enzymes, and none heterologous and secretory expression of alkaline ?-mannanase in Bacillus subtilis expression system was reported. Alkaliphilic Bacillus clausii S10 showed high ?-mannanase activity at alkaline condition. In this study, this ?-mannanase was cloned, purified and characterized. The high-level secretory expression in B. subtilis was also studied. RESULTS:A thermo-alkaline ?-mannanase (BcManA) gene encoding a 317-amino acid protein from alkaliphilic Bacillus clausii strain was cloned and expressed in Escherichia coli. The purified mature BcManA exhibited maximum activity at pH 9.5 and 75 °C with good stability at pH 7.0-11.5 and below 80 °C. BcManA demonstrated high cleavage capability on polysaccharides containing ?-1,4-mannosidic linkages, such as konjac glucomannan, locust bean gum, guar gum and sesbania gum. The highest specific activity of 2366.2 U mg-1 was observed on konjac glucomannan with the Km and kcat value of 0.62 g l-1 and 1238.9 s-1, respectively. The hydrolysis products were mainly oligosaccharides with a higher degree of polymerization than biose. BcManA also cleaved manno-oligosaccharides with polymerization degree more than 3 without transglycosylation. Furthermore, six signal peptides and two strong promoters were used for efficiently secreted expression optimization in B. subtilis WB600 and the highest extracellular activity of 2374 U ml-1 with secretory rate of 98.5% was obtained using SPlipA and P43 after 72 h cultivation in 2?×?SR medium. By medium optimization using cheap nitrogen and carbon source of peanut meal and glucose, the extracellular activity reached 6041 U ml-1 after 72 h cultivation with 6% inoculum size by shake flask fermentation. CONCLUSIONS:The thermo-alkaline ?-mannanase BcManA showed good thermal and pH stability and high catalytic efficiency towards konjac glucomannan and locust bean gum, which distinguished from other reported ?-mannanases and was a promising thermo-alkaline ?-mannanase for potential industrial application. The extracellular BcManA yield of 6041 U ml-1, which was to date the highest reported yield by flask shake, was obtained in B. subtilis with constitutive expression vector. This is the first report for secretory expression of alkaline ?-mannanase in B. subtilis protein expression system, which would significantly cut down the production cost of this enzyme. Also this research would be helpful for secretory expression of other ?-mannanases in B. subtilis.

SUBMITTER: Zhou C 

PROVIDER: S-EPMC6087540 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature