Exploring Ectoine Production From Methanol, Formate, and Electrochemically Produced Formate by <i>Methyloligella halotolerans</i>

Microbial synthesis using renewable C₁-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 <i>Methyloligella halotolerans</i>. 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 C₁-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 CO₂ reduction in saline media with microbial synthesis of organic chemicals.