Abstract: To reveal the relationship between Bacillus megaterium and Gluconobacter oxydans in the mixed culture of vitamin C two-step fermentation,the effect of B.megaterium on the growth of G.oxydans and its synthesizing ability of 2-keto-L-gulonic acid(2KGA) was studied.The bioactive metabolites which could enhance the synthesis of 2KGA were isolated and purified by ultrafiltration,gel chromatography and SDS-polyacrylamide gel electrophoresis.Both the culture supernatant and the cytosol of B.megaterium could promote the proliferation of G.oxydans,and the active component in the culture supernatant was above 100 KDa.The culture suernatant could enhance the conversion of L-sorbose to 2KGA,while the cytosol could not.The active components in B.megaterium culture supernatant had molecular weight of 30～50 KDa and above 100 KDa,and the former was a kind of protein with an apparent molecular weight of about 35 KDa,which consisted of one sort of subunit and contained Fe and Zn elements.

Key words: Proliferation, 2-keto-L-gulonic acid, Mixed culture, Gluconobacter oxydans, Bacillus megaterium