Energy metabolism and intracellular pH regulation reveal different physiological acclimation mechanisms of Chlorella strains to high concentrations of CO2

Isolation and Whole-genome analysis of Desmodesmus sp. SZ-1: Novel acid-tolerant carbon-fixing microalga

Utilizing microalgae to capture flue gas pollutants is an effective strategy for mitigating greenhouse gas emissions. However, existing carbon-fixing microalgae exhibit poor tolerance towards acidic flue gas. In this study, the Desmodesmus sp. SZ-1, which can thrive in acidic environments and efficiently sequester CO2, was isolated. Desmodesmus sp. SZ-1 exhibited strong acid tolerance ability, with an average carbon fixation rate of 497.6 mg/L/d under 10 % CO2 and pH 3.5. Physiological analysis revealed that SZ-1 responded to high CO2 by increasing chlorophyll levels while coping with acidic stress by activating antioxidant enzymes. Genome analysis revealed a large number of carbon fixation and acid adaptation genes, involved in membrane lipid biosynthesis, H+ pumps, molecular chaperones, peroxidase system, amino acid synthesis, and carbonic anhydrase. This study provides a novel algal resource for mitigating acid gas emissions and a comprehensive genetic database for genetically modifying microalgae.

Production of eicosapentaenoic acid by Vacuoliviride crystalliferum under 20% CO2 conditions

Utilizing flue gas CO2 to co-produce eicosapentaenoic acid (EPA) with microalgae is considered an ideal approach for combating climate change and reducing cultivation costs. However, microalgal species that can efficiently produce EPA under high-CO2 conditions are scarce. This study identified that the eustigmatophycean strain Vacuoliviride crystalliferum demonstrates rapid growth under 20 % CO2 conditions (0.22 vvm), achieving a biomass concentration and productivity of 3.90 g/L and 229.26 mg/L/d, respectively. The EPA content and EPA productivity were found to be 4.28 % (w/w) and 9.80 mg/L/d, respectively. Additionally, an improved biomass concentration of 3.39 g/L and EPA content and productivity of 4.32 % (w/w) and 11.28 mg/L/d were obtained in a 30 L up-scaled cultivation system. Taken together, these findings suggest that V. crystalliferum is a promising candidate for integrating flue gas sequestration with EPA production.

Insight into the potential mechanism of bicarbonate assimilation promoted by mixotrophic in CO2 absorption and microalgae conversion system

CO2 absorption-microalgae conversion (CAMC) system is a promising carbon capture and utilization technology. However, the use of HCO3- as a carbon source often led to a slower growth rate of microalgae, which also limited the application of CAMC system. In this study, the assimilation efficiency of HCO3- in CAMC system was improved through mixotrophic, and the potential mechanism was investigated. The HCO3- assimilation efficiency and biomass under mixotrophic were 34.79% and 31.76% higher than that of control. Mixotrophic increased chlorophyll and phycocyanin content, which were beneficial to capture more light energy. The content of ATP and NADPH reached 566.86 μmol/gprot and 672.86 nmol/mgprot, which increased by 31.83% and 27.67% compared to autotrophic. The activity of carbonic anhydrase and Rubisco increased by 18.52% and 22.08%, respectively. Transcriptome showed that genes related to photosynthetic and respiratory electron transport were up-regulated. The synergy of photophosphorylation and oxidative phosphorylation greatly improved energy metabolism efficiency, thus accelerating the assimilation of HCO3-. These results revealed a potential mechanism of promoting the HCO3- assimilation under mixotrophic, it also provided a guidance for using CAMC system to serve carbon neutrality.

Nitrogen addition effect overrides warming effect on dissolved CO2 and phytoplankton structure in shallow lakes

Shallow lakes are numerous in all climate zones, but our knowledge about their dissolved carbon dioxide (CO2) response to future climate change and nutrient enrichment is rather limited. Here we performed a mesocosm experiment with four treatments to investigate how warming and nitrogen addition will impact the partial pressure of CO2 (pCO2) and phytoplankton community individually and combined. We found that warming alone had no significant effect on pCO2, while nitrogen addition increased pCO2 significantly. The combined effects of nitrogen addition and warming on pCO2 level were prevalent, indicating that eutrophic shallow lakes would be double-jeopardized in the future climate. Warming and nitrogen addition together also showed to have changed the phytoplankton community structure, suggesting a potential shifting of biological system in shallow lakes under changing climate. These findings highlight the importance of reducing nitrogen pollution to shallow lake systems for sustainable development goal.

Pilot-scale remediation of rare earth elements ammonium wastewater by Chlamydomonas sp. YC in summer under outdoor conditions

This work evaluated the performance of real rare earth elements (REEs) wastewater purification and carbon dioxide (CO₂) fixation by Chlamydomonas sp. YC with pilot-scale airlift-photobioreactors (AL-PBRs), tubular photobioreactors (TB-PBRs) and raceway ponds (ORWPs) under high-temperature outdoor conditions in summer. The obtained results showed that Chlamydomonas sp. YC at 1 g/L oyster shell piece (OSP) and 3 % CO₂ had the highest biomass (1.9 g/L) and NH₄⁺-N removal efficiency (34.0 %) during the REEs wastewater treatment. Among the selected photobioreactors, Chlamydomonas sp. YC to treat real REEs wastewater at 3 % CO₂ under high-temperature outdoor conditions attained the highest biomass (2.3 g/L) in the TB-PBRs with the best NH₄⁺-N removal efficiency (43.0 %). Furthermore, the input cost and CO₂ net sequestration evaluation revealed that TB-PBRs was more economical photobioreactors to treat REEs wastewater and fix CO₂ by Chlamydomonas sp. YC, providing some vital scientific details for REEs wastewater and CO₂ fixation by microalgal biotechnology.