Wu Mingcan, Wu Guimei, Lu Feimiao, Wang Hongxia, Lei Anping, Wang Jiangxin
Shenzhen Key Laboratory of Marine Bioresource and Eco-Environmental Science, Shenzhen Engineering Laboratory for Marine Algal Biotechnology, Guangdong Provincial Key Laboratory for Plant Epigenetics, College of Life Sciences and Oceanography, Shenzhen University, Shenzhen, 518060, China.
State Key Laboratory of Marine Resource Utilization in South China Sea, College of Oceanology, Hainan University, Haikou, 570228, China.
Biotechnol Biofuels Bioprod. 2022 Oct 26;15(1):115. doi: 10.1186/s13068-022-02212-z.
Microalgae can absorb CO during photosynthesis, which causes the aquatic environmental pH to rise. However, the pH is reduced when microalga Euglena gracilis (EG) is cultivated under photoautotrophic conditions. The mechanism behind this unique phenomenon is not yet elucidated.
The present study evaluated the growth of EG, compared to Chlorella vulgaris (CV), as the control group; analyzed the dissolved organic matter (DOM) in the aquatic environment; finally revealed the mechanism of the decrease in the aquatic environmental pH via comparative metabolomics analysis. Although the CV cell density was 28.3-fold that of EG, the secreted-DOM content from EG cell was 49.8-fold that of CV (p-value < 0.001). The main component of EG's DOM was rich in humic acids, which contained more DOM composed of chemical bonds such as N-H, O-H, C-H, C=O, C-O-C, and C-OH than that of CV. Essentially, the 24 candidate biomarkers metabolites secreted by EG into the aquatic environment were acidic substances, mainly lipids and lipid-like molecules, organoheterocyclic compounds, organic acids, and derivatives. Moreover, six potential critical secreted-metabolic pathways were identified.
This study demonstrated that EG secreted acidic metabolites, resulting in decreased aquatic environmental pH. This study provides novel insights into a new understanding of the ecological niche of EG and the rule of pH change in the microalgae aquatic environment.
微藻在光合作用过程中会吸收二氧化碳，这会导致水生环境的pH值升高。然而，在光自养条件下培养纤细裸藻（EG）时，pH值会降低。这一独特现象背后的机制尚未阐明。
本研究评估了EG与作为对照组的普通小球藻（CV）的生长情况；分析了水生环境中的溶解有机物（DOM）；最后通过比较代谢组学分析揭示了水生环境pH值下降的机制。尽管CV的细胞密度是EG的28.3倍，但EG细胞分泌的DOM含量却是CV的49.8倍（p值<0.001）。EG的DOM主要成分富含腐殖酸，与CV相比，其所含的由N-H、O-H、C-H、C=O、C-O-C和C-OH等化学键组成的DOM更多。从本质上讲，EG分泌到水生环境中的24种候选生物标志物代谢物均为酸性物质，主要是脂质和类脂分子、有机杂环化合物、有机酸及其衍生物。此外，还确定了6条潜在的关键分泌代谢途径。
本研究表明，EG分泌酸性代谢物，导致水生环境pH值下降。本研究为重新认识EG的生态位以及微藻水生环境中pH值变化规律提供了新的见解。
