Biomass production of hairy roots of Artemisia annua and Arachis hypogaea in a scaled-up mist bioreactor.

Hairy roots have the potential to produce a variety of valuable small and large molecules. The mist reactor is a gas phase bioreactor that has shown promise for low-cost culture of hairy roots. Using a newer, disposable culture bag, mist reactor performance was studied with two species, Artemisia annua L. and Arachis hypogaea (peanut), at scales from 1 to 20 L. Both species of hairy roots when grown at 1 L in the mist reactor showed growth rates that surpassed that in shake flasks. From the information gleaned at 1 L, Arachis was scaled further to 4 and then 20 L. Misting duty cycle, culture medium flow rate, and timing of when flow rate was increased were varied. In a mist reactor increasing the misting cycle or increasing the medium flow rate are the two alternatives for increased delivery of liquid nutrients to the root bed. Longer misting cycles beyond 2-3 min were generally deemed detrimental to growth. On the other hand, increasing the medium flow rate to the sonic nozzle especially during the exponential phase of root growth (weeks 2-3) was the most important factor for increasing growth rates and biomass yields in the 20 L reactors. A. hypogaea growth in 1 L reactors was µ = 0.173 day(-1) with biomass yield of 12.75 g DW L(-1). This exceeded that in shake flasks at µ = 0.166 day(-1) and 11.10 g DW L(-1). Best growth rate and biomass yield at 20 L was µ = 0.147 and 7.77 g DW L(-1), which was mainly achieved when medium flow rate delivery was increased. The mist deposition model was further evaluated using this newer reactor design and when the apparent thickness of roots (+hairs) was taken into account, the empirical data correlated with model predictions. Together these results establish the most important conditions to explore for future optimization of the mist bioreactor for culture of hairy roots.