Solid state bioreactor production of transglutaminase by Amazonian Bacillus circulans BL32 strain

In this work, we investigated the production of transglutaminase (TGase) by an Amazonian isolated strain of Bacillus circulans by solid-state cultivation (SSC). Several agro-industrial residues, such as untreated corn grits, milled brewers rice, industrial fibrous soy residue, soy hull, and malt bagasse, were used as substrates for microbial growth and enzyme production. Growth on industrial fibrous soy residue, which is rich in protein and hemicellulose, produced the highest TGase activity (0.74 U g⁻¹ of dried substrate after 48 h of incubation). A 2³ central composite design was applied to determine the optimal conditions of aeration, cultivation temperature and inoculum cell concentration to TGase production. The best culture conditions were determined as being 0.6 L air min⁻¹, 33 °C and 10 log ₁₀ CFU g⁻¹ of dried substrate, respectively. Under the proposed optimized conditions, the model predicted an enzyme production of 1.16 U g⁻¹ of dried substrate, closely matching the experimental activity of 1.25 U g⁻¹. Results presented in this work point to the use of this newly isolated B. circulans strain as a potential alternative of microbial source for TGase production by SSC, using inexpensive culture media.