大气CO2浓度上升对蓝藻产生微囊藻毒素不同变体的影响研究

Cyanobacteria are able to produce microcystins, a type of natural toxins that are most widely distributed in freshwater and can cause serious damage to human health. Due to changes in their amino acids composition, microcystins can have many variants. These variants differ in their toxicity. Microcystins as a family of oligopeptides, have been intensively studied, however, little is known about how these different variants are produced. According to the carbon-nutrient balance hypothesis, nutrients limitation favor carbon-based metabolites whereas nitrogen-rich metabolites are favored in fertile ecosystems. Under global change, constantly rising in atmospheric CO2 level will increases the carbon availability for autotrophic organisms, which will dis-equilibrate the balance between carbon and nutrients. In this proposal, we aim to test the hypothesis that under elevated CO2 level, cyanobacteria will produce more microcystin variants with high C:N ratio. High C:N ratio variants usually are more toxic. Therefore, elevated atmospheric CO2 level in the future, may not only alleviate the C limitation during the cyanobacteria bloom, but also may increase the toxicity of the bloom. This will give us a better understanding about cyanobacteria bloom and its potential consequence in response to global change.

微囊藻毒素是蓝藻分泌的一种天然毒素，在淡水环境中分布及危害最为广泛。根据氨基酸组成的不同，其可形成多种变体，且不同变体的毒性相差较大。微囊藻毒素作为寡肽类物质，其产生机制已被广泛研究，然而对其不同变体产生机制的研究却甚少。碳-营养平衡假说认为，碳与营养盐的相对获得性决定了植物次级代谢产物的合成。即当营养盐限制时，植物倾向于合成富含碳的次级代谢产物；当营养盐过量时，倾向于合成富含氮的次级代谢产物。当前大气CO2浓度持续上升，这将打破现有的碳与营养盐平衡。本项目将研究CO2浓度升高对蓝藻的次级代谢产物——微囊藻毒素不同变体产生的影响。提出假设：大气CO2浓度升高，有利于高C:N比毒素变体的合成。高C:N比的毒素变体通常毒性较大，因此得出推论：大气CO2浓度上升不仅可以缓解蓝藻水华时的碳限制，而且可以使产生的微囊藻毒素毒性增强。本项目的开展有助于更好地了解蓝藻水华及其危害在全球变化背景下的响应。

本项目在全球变化的背景下，研究了大气CO2浓度升高对蓝藻产生微囊藻毒素的影响。通过控制CO2浓度和利用恒化器技术，系统的研究了CO2浓度升高对微囊藻毒素合成、组成及毒性的影响。研究结果表明：CO2浓度升高有利于高C:N比毒素变体的合成。然而高C:N比的毒素变体通常毒性较大，因此大气CO2浓度上升不仅可以缓解蓝藻水华时的碳限制，而且可以使产生的毒素毒性增强。这与本研究的假设结果相符，项目获得了预期的实验结果，使我们可以进一步解了蓝藻水华及其危害在全球变化背景下的响应。