Bacillus spp. is widely used as the companion bacterium in the two-step biosynthesis of 2-keto-L-gulonic acid (2-KLG), which is the direct precursor in the production of vitamin C by Ketogulonigenium vulgare. To understand the effects of sporulation and spore stability on 2-KLG production, the spo0A and spoVFA deletion mutants of Bacillus megaterium were constructed. The sorbose conversion rates of spo0A and spoVFA mutant co-culture systems were 33% and 70% lower, respectively, than that of the wild-type co-culture system. In addition, K. vulgare cell numbers in the two mutant systems declined by 15% and 49%, respectively, compared to the value in the wild-type system. Correlation analysis indicated that the 2-KLG concentration is positively related to sorbose dehydrogenase activity and the K. vulgare cell number. This study demonstrated that sporulation and spore stability of the wild-type companion play key roles in the enhancement of K. vulgare propagation and 2-KLG biosynthesis. (C) 2011 Elsevier Ltd. All rights reserved.