Extracellular production of Streptomyces ladakanum transglutaminase in a food-grade strain, Bacillus subtilis

Background: Transglutaminase (TG) is an enzyme of the transferase family with cross-linking properties, which has been widely used in the food industry. Traditionally, TG is isolated from strains of Streptomyces sp. However, the development of a facile and efficient production of commercial TG is always desirable. Purpose: In the current study, we described an efficient route for TG production in a food-grade strain of bacteria, Bacillus subtilis. Method: Two strategies were employed for the extracellular production of S. ladakanum TG in B. subtilis. Sixteen signal peptides were optimized to secret TG into the extracellular medium. Site-directed mutageneses in pro-peptide were further utilized to improve the enzymatic activity. The enzymatic characteristics of S. ladakanum TG expressed in B. subtilis were analyzed. Results: The N-terminal amino acids played important roles in enzymatic activity. Signal peptides of SacB (SPSacB) and AbnA (SPAbnA) showed good abilities to direct the secretion of TG into the medium. The enzyme was secreted into the medium and exhibited good Ca stability and temperature stability, which were comparable to those produced by commercial strains. The enzymatic activity in the supernatant of culture reached 7.6 U/mg. Conclusion: Our study demonstrated that B. subtilis may be a good candidate for the efficient and stable production of TG and has a much easier purification process.