The inhibition of mevalonate kinase (MVK) by downstream metabolites is an important mechanism in the regulation of isoprenoid production in a broad range of organisms. The first feedback-resistant MVK was previously discovered in the methanogenic archaeon Methanosarcinamazei. Here, we report the cloning, expression, purification, kinetic characterization and inhibition analysis of MVKs from two other methanogens, Methanosaetaconcilii and Methanocellapaludicola. Similar to the M. mazei MVK, these enzymes were not inhibited by diphosphomevalonate (DPM), dimethylallyl diphosphate (DMAPP), isopentenyldiphosphate (IPP), geranylpyrophosphate (GPP) or farnesylpyrophosphate (FPP). However, they exhibited significantly higher affinity to mevalonate and higher catalytic efficiency than the previously characterized enzyme.

Aims Establishment of an efficient isoprene fermentation process by adopting inorganic phosphate limitation as the trigger to direct metabolic flux to the isoprene synthetic pathway. Methods and Results 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. Conclusions 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. Significance and Impact of the Study This Pi‐dependent dual‐phase fermentation process could be an attractive and economically viable option for the production of various commercially valuable isoprenoids.

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