Roles of culture media and oxygen transfer in the scale-up from shake flasks to pneumatic bioreactor of the plant growth-promoting bacterium rhizobium phaseoli

Abstract

The success of a Rhizobium sp. inoculant depends on a product with a high number of live bacteria that can nodulate a leguminous plant. With the idea of developing a functional biofertilizer with a long shelf-life 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 bubble column bioreactor (BCB). The effects of carbon and phosphate on R. phaseoli growth were evaluated, and the specific volumetric oxygen transfer coefficient (kLa) was determined as a criterion to scale-up to BCB. 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 and was used to produce a biofertilizer in BCB. 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.