Production of β-glucan and related glucan-hydrolases by Botryosphaeria rhodina

Aims:  Characterization of β-glucan production from Botryosphaeria rhodina DABAC-P82 by detecting simultaneously glucan-hydrolytic enzymes and their localization, culture medium rheology and oxygen transfer. Methods and Results:  Mycelium growth, β-glucan production, substrate consumption and glucan-hydrolytic enzymes were monitored both in shaken flasks and in a 3-l stirred-tank bioreactor. Glucan production (19·7 and 15·2 g l−1, in flask and bioreactor, respectively) was accompanied by extra-cellular and cell-bound β-glucanase and β-glucosidase activities. In the bioreactor scale, in the time interval of 0–78 h the apparent viscosity of the culture broth exhibited a general increase; thereafter, it began to reduce, probably because of the above glucan-hydrolytic activities. Moreover, the culture media collected after 45 h behaved as solid-like materials at shear rates smaller than 0·001 s−1, as pseudo-plastic liquids in the middle shear rate range and as Newtonian ones at shear rates greater than 1000 s−1. Conclusion:  The greatest β-glucan accumulation in the bioreactor was found to be associated with nitrogen and dissolved oxygen concentrations smaller than 0·15 g l−1 and 25%, respectively, and with the peak points of the glucan-degrading enzymes. Significance and Impact of the Study:  A careful analysis of the critical factors (such as, culture broth rheology, oxygen mass transfer and glucan-hydrolytic enzymes) limiting the β-glucan production by B. rhodina is a prerequisite to maximize β-glucan yield and production, as well as to define the process flow sheet capable of maximizing biopolymer recovery, solvent re-utilization and glucose consumption.