Optimized Continuous Bioproduction of Ectoine from Carbon Dioxide and Industrial Contaminants Using Guyparkeria halophila

Abstract

The production of high-value compounds such as ectoine in the pharmaceutical industry faces significant challenges, including high costs, resource intensity and reliance on refined sugars. This study presents a novel bioproduction platform converting carbon dioxide (CO2) and the industrial contaminant thiosulfate (S2O32-) into ectoine using the halophilic strain Guyparkeria halophila. To overcome limitations in biomass accumulation and incomplete S2O32- oxidation, cultivation and operational parameters, including S2O32- loading rate, pH, and dilution rate, were systematically optimized in continuous stirred tank reactors. A S2O32- loading rate of 5 g d-1 supported higher specific ectoine accumulation and promoted complete S2O32- oxidation, while a moderate pH increase up to 7.6 further improved CO2 assimilation. Additionally, implementing a prior semi-batch operation followed by a low dilution rate stage (0.10 d-1) effectively enhanced biomass and ectoine productivity. Under these optimized conditions, biomass accumulation increased significantly to 290.0 ± 20.2 mg L-1, with specific ectoine contents of 387.3 ± 23.1 mgEct gbiomass-1 and productivities of 10.6 ± 0.6 gEct m-3 d-1. This work demonstrated a scalable, efficient and sustainable platform for ectoine biosynthesis that integrates CO2 valorization and industrial by-product utilization, highlighting the potential of halophilic microbes for greener and economically viable pharmaceutical manufacturing.