Combined transcriptome and metabolome analysis of a new species of microalgae from Tibetan plateau and its response to sewage treatment

Microalgae are pivotal in maintaining water quality in the lakes and rivers of Qinghai-Tibet plateau. The optimum sewage treatment conditions for Desmodesmus sp. are, temperature: 20-25{degrees}C, light intensity: 3000-8000 lx, and pH: 7.0-7.5, identified based on orthogonal experiments. The maximum removal rate of total nitrogen, total phosphorus, and chemical oxygen demand was more than 95% in the actual sewage treatment. The sewage treatment capacity of Desmodesmus sp. from plateau is higher than that from plains under the same treatment conditions. To identify the differentially expressed genes and metabolites in Desmodesmus sp. in response to sewage treatment, a combination of metabolomics and transcriptomics was employed to the microalgae with and without sewage treatment. The results showed that the oxidative phosphorylation, photosynthesis, and propanoate metabolism pathways were the most significantly enriched pathways in sewage treatment. Further, the metabolism of adenosine diphosphate, 2-oxobutanoate, and succinate were significantly upregulated, downregulated, and both upregulated and downregulated, respectively, as shown by the combined transcriptome and metabolome analysis. Additionally, we found that sewage treatment could also induce numerous changes in the primary metabolism, such as carbohydrate, fatty acid biosynthesis, and amino acid metabolism when compared with control. Overall, our results should improve fundamental knowledge of molecular responses to Desmodesmus sp. in sewage treatment and contribute to the design of strategies in microalgae response to sewage treatment.