Abstract
Submerged cultivation of edible filamentous fungi (Agaricomycetes) in bioreactors enables maximum mass transfer of nutrients and has the potential to increase the volumetric productivity of fungal biomass compared to solid state cultivation. These aspects are paramount if one wants to increase the range of bioactives (e.g. glucans) in convenient time frames. In this study, Trametes versicolor (M9911) outperformed four other Agaricomycetes tested strains (during batch cultivations in an airlift bioreactor). This strain was therefore further tested in semi-continuous cultivation. Continuous and semi-continuous cultivations (driven by the dilution rate, D) are the preferred bioprocess strategies for biomass production. We examined the semi-continuous cultivation of T. versicolor at dilution rates between 0.02 and 0.1 h-1. A maximum volumetric productivity of 0.87 g/L/h was obtained with a D of 0.1 h-1 but with a lower total biomass production (cell dry weight, CDW 8.7 g/L) than the one obtained at lower dilution rates (12.3 g/L at D of 0.04 and vs 13.4 g/L, at a D of 0.02 h-1). However, growth at a D of 0.1 h-1 resulted in a very short fermentation (18 h) which terminated due to washout (the specific D exceeded the maximum growth rate of the fungal biomass). At a D of 0.04 h-1, a CDW of 12.3 g/L was achieved without compromising the total residence time (184 h) of the fermentation. While the D of 0.04 h-1 and 0.07 h-1 achieved comparable volumetric productivities (0.5 g/L/h), the total duration of the fermentation at D of 0.07 h-1 was only 85 h. The highest glucan content of cells (27.8 as percentage of CDW) was obtained at a D of 0.07 h-1, while the lowest glucan content was observed in T. versicolor cells grown at a D of 0.02 h-1. KEY POINTS: • The highest reported volumetric productivity for fungal biomass was 0.87 g/L/h. • Semi-continuous fermentation at D of 0.02 h-1 resulted in 13.4 g/L of fungal biomass. • Semi-continuous fermentation at D of 0.07 h-1 resulted in fungal biomass with 28% of total glucans.