Comprehensive transcriptomic and metabolomic insights into simultaneous CO sequestration and nitrate removal by the Chlorella vulgaris and Pseudomonas sp. consortium.

Simultaneous CO sequestration and nitrate removal can be achieved by co-cultivation of Chlorella vulgaris with Pseudomonas sp. However, a comprehensive understanding of the synergistic mechanism between C. vulgaris and Pseudomonas sp. remains unknown. In this study, transcriptomics and metabolomics analysis were employed to elucidate the synergistic mechanism of C. vulgaris and Pseudomonas sp. Transcriptomic and metabolomic analyses identified 3664 differentially expressed genes and 314 metabolites. Transcriptome analysis revealed that co-culture with Pseudomonas sp. promoted the photosynthesis of C. vulgaris by promoting the synthesis of photosynthetic pigments and photosynthesis-antenna proteins. Furthermore, it stimulated pathways associated with energy metabolism from carbon sources, such as the Calvin cycle, glycolytic pathway, and TCA cycle. Additionally, Pseudomonas sp. reduced nitrate levels in the co-culture system by denitrification, and microalgae regulated nitrate uptake by down-regulating the transcript levels of nitrate transporter genes. Metabolomic analysis indicated that nutrient exchange was conducted between algae and bacteria, and amino acids, phytohormones, and organic heterocyclic compounds secreted by the bacteria promoted the growth metabolism of microalgae. After supplementation with differential metabolites, the carbon fixation rate and nitrate removal rate of the co-culture system reached 0.549 g L d and 135.4 mg L d, which were increased by 20% and 8%, respectively. This study provides a theoretical insight into microalgae-bacteria interaction and its practical application, as well as a novel perspective on flue gas treatment management.