Metabolomic analysis improves bioconversion of methanol to isobutanol in Methylorubrum extorquens AM1

Background Methylorubrum extorquens AM1 can be engineered to convert methanol to value-added chemicals. Most of these chemicals derive from acetyl-CoA involved in the serine cycle. However, recent studies on methylotrophic metabolism have suggested that C3 pyruvate is a good potential precursor for broadening the types of synthesized products. Methods and Results In the present study, we found that isobutanol was a model chemical that could be generated from pyruvate through a 2-keto acid pathway. Initially, the engineered M. extorquens AM1 could only produce a trace amount of isobutanol at 0.62 mgL(-1) after introducing the heterologous 2-ketoisovalerate decarboxylase and alcohol dehydrogenase. Furthermore, the metabolomic analysis revealed that insufficient carbon fluxes through 2-ketoisovalerate and pyruvate were the key limitation steps for efficient biosynthesis of isobutanol. Based on this analysis, the titer of isobutanol was improved by over 20-fold after overexpressing alsS gene encoding acetolactate synthase and deleting ldhA gene for lactate dehydrogenase. Moreover, substituting the cell chassis with the isobutanol-tolerant strain isolated from adaptive evolution of M. extorquens AM1 further increased the production of isobutanol by 1.7-fold, resulting in the final titer of 19 mgL(-1) in flask cultivation. Conclusion Our current findings provided promising insights into engineering methylotrophic cell factories capable of converting methanol to isobutanol or value-added chemicals using pyruvate as the precursor.

Automated summary

The study investigated the potential of using pyruvate to produce isobutanol in engineered Methylorubrum extorquens AM1. By optimizing the metabolic pathways and utilizing an isobutanol-tolerant strain, the production of isobutanol was significantly increased, showcasing the feasibility of converting methanol to valuable chemicals using pyruvate as a precursor.