Simplified bioreactor processes for recombinant butyrylcholinesterase production in transgenic rice cell suspension cultures

Metabolically regulated transgenic rice cell suspension culture has been developed aiming to be an efficient and cost-effective platform for production of rice-recombinant butyrylcholinesterase (rrBChE) that could be used as a bioscavenger enzyme against organophosphate nerve agents. In two-stage batch cultures, switching between growth and induction phases by exchanging media, the maximum active rrBChE levels were comparable among the bioreactor runs with controlled dissolved oxygen (DO) concentrations from 10-40% DO and without controlled DO at constant aeration rate. For a single-stage batch operation with no media exchange at 40% DO, production of rrBChE is triggered simply through sugar depletion due to the uptake of sugar by the cells, showing similar maximum active cell-associated rrBChE level compared to two-stage batch operations. However, the bioreactor process using uncontrolled DO, no media exchange, and half-concentration of sucrose resulted in a 1.4-fold increase in the maximum total active rrBChE (77 mu g/g fresh weight) and 1.6-fold increase of total active rrBChE specific productivity (86 mu g (g dry weight)(-1) day(-1)) compared to the two-stage batch cultures. We found that monitoring the culture pH is a simple non-invasive technique that can help identify the start and progress of the induction phase in a single-stage culture. Altogether, we demonstrate a simplified, efficient, economical, and scalable bioreactor process for rrBChE production in metabolically regulated transgenic rice cell cultures.