Continuous abatement of methane coupled with ectoine production by Methylomicrobium alcaliphilum 20Z in stirred tank reactors: A step further towards greenhouse gas biorefineries

This study demonstrates for the first time the feasibility of producing ectoine (a high added value osmoprotectant intensively used in the cosmetic industry) during the continuous abatement of diluted emissions of methane by Methylomicrobium alcaliphilum 20Z in stirred tank reactors under non-sterile conditions. An increase in NaCl concentration in the cultivation broth from 3 to 6% increased the intra-cellular ectoine yield by a factor of 2 (from 16.5 to 37.4 mg ectoine (g biomass)⁻¹), while high stirring rates (600 rpm) entailed a detrimental cellular stress and 3 times lower ectoine yields (5.6 mg ectoine (g biomass)⁻¹) compared to process operation at 300 rpm. An increase in Cu²⁺ concentration from 0.05 to 25 μM enhanced methane abatement by a factor of 2 (up to elimination capacities of 24.5 g m⁻³ h⁻¹), did not enhance intra-cellular ectoine production but promoted the excretion to the cultivation broth of 20% of the total ectoine synthesized regardless of the NaCl concentration and stirring rate. The results obtained by culture hybridization with the specific probe Mγ1004 showed that Methylomicrobium alcaliphilum 20Z accounted for more than 80% of the total bacterial population in most experimental runs. This work confirmed the technical feasibility of a new generation of biorefineries based on the abatement of diluted CH₄ emissions using extremophile methanotrophs.