Abstract: Strain ND2 with the highest activity of the enzyme was screened from the sale natto, and was characterized as Bacillus subtilis sp. by physiologic and biochemical characteristics and analysis of 16SrRNA sequences. The optimal condition for natto kinase (NK)-fermenting was determined as follow: soybean as nitrogen source, fecula as carbon source, carbon-nitrogen ratio 3:1, 37℃, and pH6.0. The NK gene (825bp) was amplified from strain ND2 through PCR reaction. And SDS PAGE analysis revealed that using the pET32a(+) as expression vector and BL21(DE3) as host strain and cultivating at 37℃ with 1‰ IPTG, recombinant NK protein was highly expressed.

Key words: Bacillus subtilis sp., natto kinase, gene clone and expression