Inoculum production of the ectomycorrhizal fungus Pisolithus microcarpus in an airlift bioreactor.

Many important tree species in reforestation programs are dependent on ectomycorrhizal symbiosis in order to survive and grow, mainly in poor soils. The exploitation of this symbiosis to increase plant productivity demands the establishment of inoculum production methods. This study aims to propose an inoculum production method of the ectomycorrhizal fungus Pisolithus microcarpus (isolate UFSC-Pt116) using liquid fermentation in an airlift bioreactor with external circulation. The fungus grew as dark dense pellets during a batch fermentation at 25.5 degrees C and air inlet of 0.26-0.43 vvm. The maximum biomass (dry weight) achieved in the airlift bioreactor was approximately 5 g.l(-1) after 10-11 days. The specific growth rate (micro(x)) in the exponential phase was 0.576 day(-1), the yield factor (Y(X/S)) 0.418, and the productivity (P(X)) 0.480 g.l(-1).day(-1). This specific growth rate was higher than that observed by other authors during fermentation processes with other Pisolithus isolates. The method seems to be very suitable for biomass production of this fungus. However, new studies on the fungus growth morphology in this system, as well as on the efficiency of the process for the cultivation of other ectomycorrhizal fungi, are necessary. It is also necessary to test the infectivity and efficiency of the inoculum towards the hosts.