Medium redesign for stable cultivation and high production of mevalonate by recombinant Methtylobacterium extorquens AM1 with mevalonate synthetic pathway

Methylobacterium extorquens AM1 (AM1) has shown promise for use in industry due to its ability to use methanol as a sole carbon and energy source. Mevalonic acid (MEV) is an important platform chemical for the biosynthesis of isoprenoids, and a building block in the synthesis of polymers. In our previous study, the growth and MEV production of AM1-dcel-mvt strain were found to be unstable in the culture media tested (CHOI, MP, MC and HP), which contained ammonium salts, magnesium, calcium, buffers, methanol and trace elements. In this study, we developed a novel MC medium based on MP and CHOI, which improved the growth rate and the reproducibility and replicability of culture process considerably. AM1-dcel-mvt cells cultivated in MC displayed a more homogenous doubling time than cells in other media, which could explain their more stable growth. The optimized MO medium containing a higher phosphate buffer concentration and lower trace elements was developed, which enhanced MEV production by 0.61-fold to 340 mg/L. In fed-batch fermentation in a 5 L fermenter, a MEV titre of 2.59 g/Land a dry cell weight (DCW) of 9.03 g/L were obtained, representing the highest MEV production reported to date for the AM1-dcel-mvt strain. The MO medium facilitate the stable growth of AM1, and improve the industrial-scale production of MEV.