Diffusional and transcriptional mechanisms involved in laccases production by Pleurotus ostreatus CP50

• Opposite effects of EDCF and DOT on fungal physiology were observed.
• DOT above 8% negatively affects poxc transcription and laccase specific production.
• EDCF positively affects fungal growth and laccase specific production.
• Cultures <11 kW/m3s EDCF produce pellets with diffusional limitations.
• DOT effects were transcriptional whereas EDCF effects were mainly physical.

The independent effects of hydrodynamic stress (assessed as the Energy Dissipation/Circulation Function, EDCF) and dissolved oxygen tension (DOT) on the growth, morphology and laccase production by Pleurotus ostreatus CP50 were studied using a 32 factorial design in a 10 L reactor. A bell-shape function for fungus growth between 8 and 22% DOT was observed, as well as a significant negative effect on laccase production and the expression of poxc, the gene encoding for the most abundant laccase produced by P. ostreatus CP50. Increasing EDCF from 1 to 21 kW/m3 s, had a positive effect on fungus growth, whereas no effect on poxc gene expression was observed. However, the increase in EDCF favored the specific laccase production due to the generation of smaller pellets with less diffusional limitations and increased metabolically active biomass.The results show, for the first time, that hydrodynamic effects on growth and laccase production are mainly physical and diffusional, while the influence of the dissolved oxygen is at transcriptional level.