Gradual salinity acclimation drives continuous co-production of ectoine and microbial proteins from carbon dioxide.

Transforming carbon dioxide (CO2) into high-value products remains a major challenge for next-generation biorefineries, largely due to the limited robustness and stability of current microbial systems. Among the most promising targets, ectoine and microbial proteins (MPs) stand out for their high value in pharmaceutical and nutraceutical applications. However, low productivity and growth inhibition continue to constrain the scalability of CO2-based bioprocesses. This study presents a bioproduction strategy based on gradual salinity acclimation of a salinity-selected halophilic microbial consortium, initially inoculated with a defined co-culture, for the continuous co-production of ectoine and MPs from CO2 and hydrogen (H2). Salinity was applied as a selective pressure to restructure the microbial community and influence carbon allocation, while its gradual increase enabled adaptation to increasing stress conditions and stable operation without accumulation of inhibitory metabolites. This resulted in a maximum ectoine productivity of 8.3 ± 0.1 mgEct L-1 d-1 and a specific ectoine content of 22.6 ± 1.4 % (w/w) at 8 % NaCl, while consistently sustaining high MP levels (63.3 ± 3.0 % w/w). Notably, system performance was maintained through community shifts that led to the enrichment of a more halotolerant consortium, allowing continued production of both compounds. These results demonstrate that gradual salinity acclimation provides an effective and practical strategy to sustain productivity and enable CO2-based bioproduction under salinity stress, supporting the development of more robust and adaptable bioprocesses.