Metagenomics and metatranscriptomics insights into microbial enhancement of H₂S removal and CO₂ assimilation

This study focuses on the coupled process of bio-enhanced absorption and biodesulfurization for the toxic gas H₂S and the greenhouse gas CO₂. The results show that on the basis of stabilized absorption of H₂S and CO₂ by alkaline solution (Stage I), the addition of air-lift bioreactor process solution in the absorption column enhanced their absorption (Stage II). Specifically, at constant inlet concentrations of H₂S and CO₂ of 3% (30,000 ppmv) and 30% (300,000 ppmv), respectively, the outlet gases were primarily H₂S, CO₂, and N₂. And the outlet H₂S and CO₂ concentrations decreased from 10,038 ± 1166 ppmv and 49,897 ± 2545 ppmv in Stage I to 940 ± 163 ppmv and 21,000 ± 2165 ppmv in Stage II. S⁰-producing performance (348 ± 20-503 ± 23 mg S/L) and biomass concentration (467 ± 13-677 ± 55 mg/L) in the subsequent bioreactor also increased in response to the enhanced absorption of H₂S and CO₂. Biologically enhanced H₂S and CO₂ absorption differs from physicochemical factors in that it depends on several physiological parameters such as microbial community composition and gene expression levels. In this study, the sulfur autotrophic denitrifying bacteria Thioalkalivibrio and Arenimonas had high abundance and activity (abundance: 69.5% and 21.1%, expression: 82.4% and 13.9%), and they were the main contributors to the bio-enhanced absorption of H₂S and CO₂ in this system. In addition, the main factor for enhanced H₂S absorption could be the high expression of sulfide:quinone oxidoreductase (SQR, encoding gene sqr) (45 ± 9 to 821 ± 102 transcripts per million). Enhanced CO₂ absorption could have been achieved by the oxidation of more H₂S generating more energy to increase the carboxylation activity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, encoding genes rbcLS). Enhanced H₂S absorption enhances CO₂ absorption and facilitates microbial growth, which in turn benefits the metabolism of H₂S, creating a complementary biologically enhanced absorption. This study provides a novel strategy, demonstrating the potential of autotrophic sulfide-oxidizing microorganisms in the simultaneous removal of H₂S and assimilation of CO₂, and offers a deeper understanding of the underlying mechanisms.