Screening Bacillus subtilis for Effective L-theanine Production from Tea Plant Rhizosphere Soil

L-theanine is used as an additive in food industry due to its unique health benefits to human being. Using gamma-glutamyltranspeptidase (GGT) for L-theanine biosynthesis is one of the most effective methods. Fifty putative Bacillus strains were isolated from tea plant rhizosphere soil and could produce GGT but differed in GGT-producing activity. The capacity of forming L-theanine activity catalyzed by the GGTs from different strains was consistent with their activity of producing GGTs. Strain BSFT-42 was identified as Bacillus subtilis based on biochemical properties and 16S rDNA sequence alignment. The GGT produced by this strain had the highest L-theanine-forming activity. Under the optimized conditions, the GGT from the fermentation broth of strain BSFT-42 at 32 h could convert 87.45% of Gln to L-theanine and produced 17.49 mM of L-theanine. This study indicated the possibility to use GGT excreted by B. subtilis BSFT-42 for L-theanine production.