Guyparkeria halophila: Novel cell platform for the efficient valorization of carbon dioxide and thiosulfate into ectoine

Utilizing carbon dioxide (CO₂) for valuable chemical production is key to a circular economy. Current processes are costly due to limited microorganism use, low-value products, and the need for affordable energy. This study addresses these challenges by using industrial contaminants like thiosulfate (S₂O₃²⁻) for CO₂ conversion into ectoines. Ectoines, are important ingredients as pharmaceuticals and cosmetics. Here, six microbial genomes were identified as potential candidates to valorize CO₂ and S₂O₃²⁻ into ectoine. After laboratory validation at 3 % NaCl, the fastest-growing strain, Guyparkeria halophila, was optimized at 6 %, 9 %, and 15 % NaCl, showing the highest specific ectoine contents (mg_Ect g_biomass⁻¹) at 15 %. Batch bioreactors, combining optimal conditions, achieved maximum specific ectoine contents of 47 %. These results not only constitute the highest ectoine content so far reported by autotrophs and most of heterotrophs, but also the first proof of a novel valorization platform for CO₂ and S₂O₃²⁻, focused on pharmaceuticals production.