Anna Antecka, Michał Blatkiewicz, Marcin Bizukojć and Stanisław Ledakowicz
Department of Bioprocess Engineering, Faculty of Process and Environmental Engineering, Lodz University of Technology, 213 Wolczanska Street, 90-924 Lodz, Poland
It is well known that productivity in biotechnological processes is often correlated with morphological form of fungi in particular in submerged cultivation. Filamentous organisms such as Aspergillus niger can grow either in dense, spherical pellets or as disperse and viscous mycelia. Freely dispersed mycelium seems favorable and regarded as prerequisite to ensure high productivity of enzymes like amylase phytase etc., or production of penicillin. The desired morphological characteristics can be achieved by variation of operating parameters. In pioneering study the use of inorganic microparticles (such as aluminium oxide or magnesium silicate) added to the culture was recently introduced to influence morphology of filamentous fungi. It was observed that intentional supplementation to the culture might generally stimulate growth of these organisms as well as increase biosynthesis of selected enzymes. Following this suggestion we attempted to apply this morphology engineering method to Basidiomycetous white rot fungi such as Cerrena unicolor and Pleurotus ostreatus, which are well known producers of very robust enzyme laccase. Laccases (EC 1.10.3.2) are copper containing oxidases that catalyze reduction of O2 to H2O using variety of phenolic substrates as hydrogen donors. Laccases are used in paper, textile bioremediation and other industries.
The influence of aluminium oxide particles (diameter 10 μm) on laccase biosynthesis and fungal morphology was studied in the shaken culture medium . The results show the positive effect of the microparticles at all tested concentrations of aluminium oxide in the range 0-30 g/L. Concentration of 15 g/l was selected as the optimal one because of highest laccase activity and complete incorporation of aluminium oxide into biomass. The higher concentration of aluminium oxide caused the decrease in pellets size and their surfaces got more hairy up to transformation into dispersed morphology at concentration of 30 g/L. The laccase activity increased up to 3.5 times at the Al2O3 concentration of 15g/L, compared to non-supplemented culture of modified Lindeberg & Holm's medium. Further increasing the concentration of aluminium oxide up to 30 g/L did influenced the morphology of fungi decreasing the size of fungi pellets, however the laccase activity was not influenced much more. Therefore the concentration 15 g Al2O3/L was chosen as the optimal one for the laccase production in the submerged cultivation.
Keywords: Laccase biosyntesis, fungal morphology, microparticle