Kinetic and Stoichiometric Analysis of Hairy Roots in a Segmented Bubble Column Reactor

Abstract

Hairy roots of Atropa belladonna were cultured in a modified 2.5‐L multicompartment bubble column for analysis of growth kinetics, stoichiometry, and atropine production. Average biomass density reached 9.9 g L⁻¹ dry weight after 43 days of batch culture; local root densities in some parts of the vessel were considerably higher, up to 17 g L⁻¹. Bulk mixing in the reactor was very poor: after 14 days of culture, the time taken to reach 95% of the equilibrium value after a concentration pulse in the vessel was 12 min. Growth and specific sugar uptake rates declined continuously throughout the culture even though adequate sugar and nitrogen remained in the medium. The observed biomass yield from sugar was approximately constant at 0.35 g g⁻¹; biomass yields from ammonia and nitrate were 0.44 and 0.35 g mmol⁻¹, respectively. Specific atropine content in the roots varied from 4.1 mg g⁻¹ dry weight at the beginning of the culture to 1.4 mg g⁻¹ after 28 days; 35 mg or 14 mg L⁻¹ atropine was produced over the 43‐day culture period. Biomass composition was represented by the elemental formula CH_1.63O_0.80N_0.13, plus 9.8% (w/w) ash. A balanced stoichiometric equation was developed for hairy root growth; this indicated that 8.3% of carbon supplied to the culture was excreted into the medium as byproducts.