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The success of a Rhizobium sp. inoculant depends on a product with a high number of live bacteria that can nodulate a leguminous plant. Culture media and oxygen transfer were studied to improve the production of R. phaseoli in chemically defined and undefined media for scale-up from shake flasks to a pneumatic bioreactor. The effects of carbon and phosphate on R. phaseoli growth were evaluated, and the specific volumetric oxygen transfer coefficient (KLa) was determined in shake flasks and scale-up to bioreactors. Six-fold more viable biomass was obtained by increasing the phosphate concentration by 7.5-fold when using glucose. However, this increase was not observed when succinate was used. In the undefined medium, glucose induced a higher production of R. phaseoli in comparison with other carbon sources. The KLa of 6–11 h-1 produced a five-fold growth of biomass in shake-flask cultures. This KLa was used to produce a R. phaseoli-based inoculant in a bioreactor. The formation of nitrogen-fixing nodules was confirmed in bean plants (Phaseolus vulgaris). The improvement of culture media with a suitable oxygen transfer demonstrates that R. phaseoli can be used as an inoculant that exerts beneficial effects on the initial growth of bean plants.

In order to increase survival rates of greenhouse seedlings destined for restoration and conservation programs, successful mycorrhization of the seedlings is necessary. To reforest forest ecosystems, host trees must be inoculated with ectomycorrhizal fungi and, in order to guarantee a sufficient supply of ectomycorrhizal inoculum, it is necessary to develop technologies for the mass production of ectomycorrhizal fungi mycelia. We selected the ectomycorrhizal fungus Laccaria trichodermophora, due to its ecological traits and feasible mycelia production in asymbiotic conditions. Here, we report the field sampling of genetic resources, as well as the highly productive nutritional media and cultivation parameters in solid cultures. Furthermore, in order to achieve high mycelial production, we used strain screening and evaluated pH, carbon source concentration, and culture conditions of submerged cultures in normal and baffled shake flasks. The higher productivity culture conditions in shake flasks were selected for evaluation in a pneumatic bioreactor, using modified BAF media with a 10 g/L glucose, pH 5.5, 25 °C, and a volumetric oxygen transfer coefficient (KLa) of 36 h−1. Under those conditions less biomass (12–37 %) was produced in the pneumatic bioreactor compared with the baffled shake flasks. This approach shows that L. trichodermophora can generate a large biomass concentration and constitute the biotechnological foundation of its mycelia mass production.

Oxygen is a key factor during free-state growth of Rhizobium phaseoli or symbiosis with common bean roots. Five different initial oxygen transfer rates (OTRI) were fix by dissolved oxygen control and constants stirrer speed rates to determine the growth of R. phaseoli in a lab-scale bioreactor. The biomass did not presented differences in the maximum concentrations for OTRI of 1.0, 1.7 and 5.9 mmol l−1 h−1. However, a sublethal effect was observed for 11.9 and 20.2 mmol l−1 h−1, where lower biomass, kinetic and stoichiometric parameters were determined. Catalase activity as an oxidative stress indicator was approximately two-fold greater with 20.2 mmol l−1 h−1 than lower OTRI. Polyhydroxybutyrate (PHB) production did not present differences in the maximum concentration. Nevertheless, an increase in PHB accumulation, yield on biomass and specific productivity were determined at the higher OTRI, suggesting a defense mechanism against oxidative stress induce by the enhancement of the oxygen transfer rates.