Production of Glomus intraradices propagules, an arbuscular mycorrhizal fungus, in an airlift bioreactor

This work addresses the symbiotic culture of the arbuscular mycorrhizal (AM ) fungus Glomus intraradices with Daucus carota hairy roots transformed by Agrobacterium rhizogenes, in two submerged culture systems: Petri dish and airlift bioreactor. AM fungi play an active role in plant nutrition and pro tection against plant pathogens. These fungi are obligate biotrophs as they depend on a host plant for their needs in carbohydrates. The effect of the mycorrhizal roots inoculum-to-medium volume ratio on the growth of both sy mbionts was studied. A critical inoculating condition was observed at simil ar to 0.6 g dry biomass (DW) . L-1 medium, above which root growth was sign ificantly reduced when using a low-salt minimal (M) liquid medium previousl y developed for hairy root-AM fungi co-culture. Below critical inoculum con ditions the maximum specific root growth and specific G. intraradices spore production rates of 0.021 and 0.035 d(-1) respectively, were observed for Petri dish cultures. Maximum spore production in the airlift bioreactor was ten times lower than that of Petri dish cultures and obtained with the low est inoculum assessed (0.13 g DW L-l medium) with 1.82 x 10(5) +/- 4.05 x 1 0(4) (SEM) spores (g DW inoculum)(-1) (L medium)(-1) in 107 d. This work pr oposes a second-generation bioprocess for AM fungi propagule production in bioreactors. (C) 1999 John Wiley & Sons, Inc.