Establishing and optimizing phloroglucinol biosynthesis from methanol in Methylobacterium extorquens AM1 via strain engineering and medium optimization.

Methanol serves as an increasingly important single-carbon feedstock that may help to facilitate the transition towards a circular bioeconomy. The Alphaproteobacterium Methylobacterium extorquens AM1 is capable of efficient growth on methanol and represents a promising chassis organism for methanol-based biotechnology. Here, we show that production of the type III polyketide synthase PhlD in M. extorquens enables the conversion of methanol into the polyketide phloroglucinol. We report that expression constructs in which phlD is placed under the control of a strong promoter are unstable. Deletion of the phaC gene, encoding for polyhydroxybutyrate synthase, does not result in increased stable phloroglucinol production. Furthermore, our results indicate that phloroglucinol is unstable in the culture medium. Its oxidative polymerization is facilitated by manganese as well as iron ions, thereby promoting the synthesis of phlorotannins. By modifying the culture medium with a decreased concentration of manganese, phloroglucinol production from methanol was increased 1.7-fold. This study reports the conversion of methanol into phloroglucinol for the first time and provides an example on the importance of the cultivation medium in the bioproduction of phenolic compounds.