Zhang Wenlin, Tan Nicole G J, Li Sam F Y
Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543.
Mol Biosyst. 2014 Jan;10(1):149-60. doi: 10.1039/c3mb70425d.
Live green algae are promising candidates for phytoremediation, but a suitable algal species which bio-accumulates high concentrations of heavy metals, and survives well in industrial water is yet to be identified. Potential metabolic engineering may be applied to improve algal phytoremediation performance, but the metal tolerance and bioaccumulation mechanisms in green algae have to be first fully understood. In this study, NMR-based metabolomics was used to study the effect of different metal species (copper, cadmium and lead) and metal concentrations in green microalgae, Chlorella vulgaris. High Cu concentrations influenced substantial decrease in organic osmolytes (betaine and glycerophosphocholine), which indicated Cu-induced redox imbalance. Accompanying redox imbalance, growth inhibition and photosynthesis impairments in Cu-spiked C. vulgaris revealed a clear relationship between Cu toxicity and redox homeostasis. As these metabolic changes were less prominent in Cd and Pb-spiked cultures, we inferred metal-specific toxicity in C. vulgaris, where redox active Cu(2+) is more potent than non-redox active Cd(2+) and Pb(2+) in causing redox imbalance. Subsequently, ICP-MS and LC-MS/MS quantification shed light on the metal-specific bioaccumulation and detoxification mechanisms. The metal bioconcentration factor (BCF) correlated well with the phytochelatin (PC) content in Cu and Cd-spiked C. vulgaris biomass. High BCF and PC levels with increasing Cu and Cd exposure concentrations indicated that PCs played a significant role in Cu and Cd bioaccumulation and detoxification. In contrast, the undetectable PC levels in Pb-spiked cultures despite high Pb BCF suggest an alternative detoxification mechanism for Pb: either by passive absorption to the algal cell wall or interaction with glutathione (GSH).
活绿藻是植物修复的理想候选者，但尚未找到一种能生物累积高浓度重金属且能在工业废水中良好存活的合适藻类。可应用潜在的代谢工程来提高藻类植物修复性能，但必须首先充分了解绿藻中的金属耐受性和生物累积机制。在本研究中，基于核磁共振的代谢组学被用于研究不同金属种类（铜、镉和铅）及金属浓度对普通小球藻这种绿微藻的影响。高铜浓度导致有机渗透物（甜菜碱和甘油磷酸胆碱）大幅减少，这表明铜诱导了氧化还原失衡。伴随氧化还原失衡，添加铜的普通小球藻出现生长抑制和光合作用受损，揭示了铜毒性与氧化还原稳态之间的明确关系。由于这些代谢变化在添加镉和铅的培养物中不太明显，我们推断普通小球藻中存在金属特异性毒性，其中具有氧化还原活性的铜离子在导致氧化还原失衡方面比无氧化还原活性的镉离子和铅离子更具效力。随后，电感耦合等离子体质谱和液相色谱 - 串联质谱定量分析揭示了金属特异性生物累积和解毒机制。金属生物浓缩系数（BCF）与添加铜和镉的普通小球藻生物量中的植物螯合肽（PC）含量密切相关。随着铜和镉暴露浓度增加，高BCF和PC水平表明PC在铜和镉的生物累积及解毒中起重要作用。相比之下，尽管添加铅的培养物中铅的BCF较高，但未检测到PC水平，这表明铅存在另一种解毒机制：要么通过被动吸附到藻细胞壁，要么与谷胱甘肽（GSH）相互作用。
