Ectoine production through a marine methanotroph-microalgae culture allows complete biogas valorization

Methanotrophs have recently emerged as a promising platform for producing bio-based chemicals, like ectoine, from biogas, offering an economical alternative to glucose. However, most studies have focused solely on CH ₄ consumption, often overlooking the CO ₂ , which is both produced by methanotrophs and present in biogas, despite its potential as a carbon source for microorganisms, such as microalgae. In this study, marine methanotrophic-microalgal cultures were enriched from environmental samples collected at the North Sea coast to explore ectoine production from both CH ₄ and CO ₂ in biogas. The sediment-derived culture exhibited the highest CH ₄ removal efficiency and CO ₂ uptake, and was selected for further experiments. The culture was primarily composed of Methylobacter marinus , Methylophaga marina , and the microalga Picochlorum oklahomensis . Gas consumption, growth, and ectoine production were evaluated under varying salinity levels and osmotic stress. The NaCl concentrations above 6% negatively impacted CH ₄ oxidation and inhibited ectoine synthesis, while osmotic shocks enhanced ectoine accumulation, with a maximum ectoine content of 51.3 mg _ectoine g _VSS ⁻¹ at 4.5% NaCl. This study is the first to report ectoine production from methanotroph-microalgal cultures, showing its potential for biogas valorization into high-value bio-based chemicals, like ectoine, marking a significant step toward sustainable biogas utilization.