High-level expression of the Streptomyces mobaraense CICC 11018 transglutaminase in Corynebacterium glutamicum ATCC 13032

The transglutaminase (MTG) secreted by Streptomyces mobaraense is a valuable enzyme for the food industry. To optimize the expression system for MTG heterologous expression in Corynebacterium glutamicum ATCC 13032, we took advantage of the recently identified efficient secretion signal peptide ΔS0949 and the tac-M promoter, a modified version of tac promoter. MTG activity assay showed that the recombinant C. glutamicum ATCC 13032 harboring plasmid pXMJ19-Spromtg which encodes the pro-MTG fused to the signal peptide ΔS0949 secreted pro-MTG to the culture broth with MTG activity of 5.2 U/mL. However, the recombinant strain pXMJ19-MSpromtg/13032 containing both the signal peptide ΔS0949 and the tac-M promoter accumulated pro-MTG up to a level of 6.7 U/mL, that resulted in an increase of 28.8% compared with the pXMJ19-Spromtg/13032 strain. Semi-quantitative RT-PCR demonstrated that transcriptional level of mtg driven by the tac-M promoter was 1.5-fold higher than that driven by the tac promoter, suggesting that, for the expression system used in this study, level of mtg transcription was a limiting factor for high-level MTG production in C. glutamicum ATCC 13032. Thus, further improvement of MTG production in the heterologous host C. glutamicum could be achieved by the use of more powerful promoters.