Abstract

This paper described the screening process of a mutant strain of Bacillus subtilisTH-49 showing specific characteristic and enhanced production of acetoin. The mutant was obtained by treating B. subtilis N-12 with ultraviolet ray (ultraviolet ray (UV)) or nitrosoguanidine (NTG) or compound mutation and subjecting it to a shake flask fermentation selection procedure. The acetoin production rate reached the highest value of 43.8 and 46.9 g/l in flask and 10-l fermenter fermentations, respectively. It was almost 4 times higher than that of the starting strain B. subtilisN-12. Through fermentation experiments, it was confirmed that the mutant strain, TH-49, was not capable of using acetoin accumulated in broth as its energy sources for growth after glucose was consumed. This phenomenon was inconsistent with that the majorities of bacteria accumulate acetoin as stored energy sources and could continue to use acetoin as energy sources after the exhaustion of glucose. By gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) analysis, it was proved that the main metabolite produced by mutant strain TH-49 was acetoin and there were no other metabolites commonly found as byproducts of acetoin fermentation, such as 2,3-butanediol and 2,3-butanedione. The above characteristic of the mutant strain, TH-49, may berelated to its specific composition of acetoin metabolism-related enzymes  system.These results indicated that, the mutant strain TH-49 is conspicuously different from other acetoin producing strains reported previously in metabolic mechanism of acetoin.

Key words: Bacillus subtilis, acetoin, mutation, mutant strain.