Toward an understanding of the effects of agitation and aeration on growth and laccases production by Pleurotus ostreatus

• Experimental design revealed complex interactions among the factors studied.
• Growth and laccase activity were influenced by agitation, aeration and Cu addition.
• Agitation and aeration had an opposite effect on growth and laccase activity.
• Laccase activity was increased at high agitation and low aeration rates.

Mycelial growth and laccase production by Pleurotus ostreatus CP50 cultured in a 10-L mechanically agitated bioreactor were assessed through a 23 factorial experimental design. The main effects and interactions of three factors (agitation, aeration and copper induction) over five responses (μ, αLacc, βLacc, maximal volumetric laccase activity and maximal biomass concentration) were analyzed. P. ostreatus growth was significantly improved when culturing was conducted with high agitation (5.9 kW/m3 s) and aeration flow (0.5 vvm) rates. Under the experimental conditions evaluated, no evidence of hydrodynamic stress affecting fungal growth was observed. However, the high agitation and aeration conditions were detrimental for the growth-associated laccase production constant (αLacc), leading to a very complex optimization of the process. The maximal laccase volumetric activity (1.2 and 3.8 U/ml for non-induced and copper-induced cultures, respectively) was observed when the culturing was performed at a low agitation rate (0.9 kW/m3 s) and a high aeration flow rate (0.5 vvm). Laccase proteolysis may explain the complex interactions observed between agitation and aeration and the effects of these factors on the laccase volumetric activity observed in the cultures.