High-yield fermentative preparation of tetramethylpyrazine by Bacillus sp. using an endogenous precursor approach

A spore-forming Bacillus sp. was isolated from a high-temperature Daqu, a starter culture of Chinese Maotai-flavor liquor, using an endogenous precursor screening strategy. The Bacillus sp. was capable of producing a high level of 2,3,5,6-tetramethylpyrazine (TTMP) via a precursor of 3-hydroxy-2-butanone (HB). The strain was characterized as Bacillus subtilis based on morphological, physiological, and biochemical properties as well as on partial 16S rRNA gene sequences. Different carbon and nitrogen sources as well as fermentation conditions were investigated. Optimization tests showed that oxygen supply and fermentation temperature were the most important parameters determining the production process. The production of >4.08 g/l TTMP was achieved together with a high level of endogenous precursor HB accumulation (>20 g/l) in both flask and fermentor cultures when the optimized medium and cultivation conditions were applied. Our data demonstrates the effectiveness of the endogenous precursor strategy for screening microorganisms that produce flavor compounds with structure-related precursors. The high yield of TTMP and the inexpensiveness of the agro-industrial product used as the substrate (soybean meal) indicate the potential of this process for industrial application.