Effects of a nutrient mist bioreactor system on growth kinetics and secondary metabolism of transformed roots of Artemisia annua

Transformed roots are a very promising source of biologically active compounds, but industriallevel production has proved very challenging. Artemisia annua produces artemisinin, a sesquiterpene lactone which is a potent antimalarial. Transformed roots of A. annua have exhibited increased levels of artemisinin when grown in a nutrient mist bioreactor. Additionally, roots showed no evidence of oxygen deprivation in this gas-phase system. Growth, however, was lower than that observed in oxygen-limited liquid-phase systems. Mathematical characterization of the mist system indicated that the root packing fraction is an important parameter in that sparsely packed roots will not capture enough mist particles to support rapid growth. We have recently shown that roots inoculated at a high packing fraction into a mist reactor grow as well as roots grown in a liquid system. Growth kinetics showed some unusual patterns of metabolism that are not the result of nutrient limitation. The results of these metabolic studies, particularly those relating to carbon uptake, should provide fundamental information for bioprocess engineering and also enhance knowledge in the field of plant biology.