Exploring Ectoine Production From Methanol, Formate, and Electrochemically Produced Formate by Methyloligella halotolerans

ABSTRACT Microbial synthesis using renewable C 1 ‐carbon sources like electrochemically produced formate (e‐formate) represents a promising approach for climate‐neutral chemical production. This study investigates formate utilization for ectoine biosynthesis by the halophilic methylotroph Methyloligella halotolerans . Preliminary growth assays confirmed formate utilization using 15–20 mM formate as the sole energy source substrate, when supplemented with yeast extract or vitamin solutions in a mineral salt medium. In a systematic study for ectoine production, formate utilization reached 0.305 ± 0.020 mmol d −1 at 20 mM. With different C 1 ‐substrates at 20 mM (3 mmol), ectoine production reached 10.3 ± 3.2 µmol (from methanol), 6.5 ± 0.8 µmol (from equimolar methanol/formate mix), 4.4 ± 0.1 µmol (from formate), and 1.2 ± 0.1 µmol (from e‐formate). Medium buffering, pH stability and toxicity limited performance when formate and e‐formate were supplied. Although ectoine yields were suboptimal, the feasibility of e‐formate‐based ectoine biosynthesis under high‐salinity conditions with 9% NaCl, as shown in this study, discloses the great potential for integrating highly efficient electrochemical CO 2 reduction in saline media with microbial synthesis of organic chemicals.