Application of inorganic phosphate limitation to efficient isoprene production in Pantoea ananatis

Establishment of an efficient isoprene fermentation process by adopting inorganic phosphate limitation as the trigger to direct metabolic flux to the isoprene synthetic pathway.

We constructed isoprene-producing strains of Pantoea ananatis (a member of the Enterobacteriaceae family) by integrating a heterologous mevalonate pathway and a metabolic switch that senses external inorganic phosphate (Pi) levels. This metabolic switch enabled dual-phase isoprene production, where the initial cell growth phase under Pi-saturating conditions was uncoupled from the subsequent isoprene production phase under Pi-limiting conditions. In fed-batch fermentation using our best strain (SWITCH-PphoC/pIspSM) in a 1-l bioreactor, isoprene concentration in the off-gas was maintained between 300 and 460 ppm during the production phase and at 20 ppm during the cell growth phase, respectively. The strain SWITCH-PphoC/pIspSM produced totally 2·5 g l^-1 of isoprene from glucose with a 1·8% volumetric yield in 48 h.

This proof-of-concept study demonstrated that our Pi-dependent dual-phase production system using a P. ananatis strain as a producer has potential for industrial-scale isoprene fermentation.

This Pi-dependent dual-phase fermentation process could be an attractive and economically viable option for the production of various commercially valuable isoprenoids.