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. Highlights Methanotroph-microalgae cultures can valorize CH 4 and CO 2 from biogas into ectoine NaCl concentrations above 6% reduced CH 4 uptake and inhibited ectoine synthesis Osmotic shock at 4.5% NaCl enhanced ectoine accumulation First report of ectoine production using methanotroph-microalgal cultures