Selection of strain and optimization of mutanase production in submerged cultures of Trichoderma harzianum.

Nineteen fungal strains belonging to different genera were tested for extracellular mutanase production in shaken flasks. The optimal enzymatic activity was achieved by Trichoderma harzianum F-470, a strain for which the mutanase productivity has not yet been published. Some of factors affecting the enzyme production in shaken flasks and aerated fermenter cultures have been standardized. Mandels mineral medium with initial pH 5.3, containing 0.25% mutan and inoculated with 10% of the 48-h mycelium, was the best for enzyme production. A slight mutanolytic activity was also found when sucrose, raffinose, lactose and melibiose were carbon sources. Application of optimized medium and cultural conditions, as well as use of a fermenter with automatic pH control set at pH 6.0 enabled to obtain a high mutanase yield (0.33 U/ml, 2.5 U/mg protein) in a short time (2-3 days). The enzyme in crude state was stable over a pH range of 4.5-6.0, and at temperatures up to 35 degrees C; its maximum activity was at 40 degrees C and at pH 5.5.