蓝藻CO2浓缩机制微进化差异及其对CO2的响应和种群演替的影响-以微囊藻为例

Because of their rapid generation times and environmental sensitivity, cyanobacteria always have substantial capacity for phenotypic plasticity and rapid evolutionary responses to environmental change. Therefore, it is a matter of concern and significance that how the microevolutionary in cyanobacterial gene responses to CO2 changes and results in population succession. A notorious bloom-forming cyanobacterium, Microcysits, is chosen to an object in this project. In this project, it is intended to study genetic diversity in CO2-concentrating mechanism (CCM) of Microcystis to observe their differences in CCM microevolutionary. On this basis, physiological and competition responses to CO2 change in different CCM genotype are also analyzed by laboratory experiments in order to explore the interspecific competition effect caused by microevolution difference of CCM. Meanwhile, to discuss the influence mechanism of CCM microevolution on the succession of Microcystis, the spatial and temporal variation characteristics and the relationship between phenotypic and CCM genotypes were also investigated by in situ monitoring of Microcystis bloom dynamic and water quality parameters. The results will not only reveal that CO2 changes may induce cyanobacteria to undergo evolutionary adaptation to cause changes in species composition and genotypes of cyanobacteria, but also provide an important theoretical basis for clarifying the impact of global change on the occurrence and succession of cyanobacteria bloom.

由于环境的敏感性及代时的短期性，蓝藻常能根据环境变化形成表型可塑性或基因快速进化。因此，蓝藻基因的微进化对CO2变化响应及其导致的种群演替是一个值得关注且有意义的问题。本项目拟以常见的水华蓝藻-微囊藻为研究对象，首先分析不同个体微囊藻的二氧化碳浓缩机制（CCM）基因多样性差异，探讨微囊藻CCM的微进化差异；在此基础上，通过室内模拟条件研究CO2浓度变化对不同CCM基因型个体的生理和竞争影响，探讨微囊藻CCM的微进化差异对CO2的响应导致的种间竞争效应；最后，通过野外微囊藻水华动态和水质参数原位监测，分析微囊藻形态型和CCM基因型的时空变化特征及相互关系，探讨微囊藻CCM微进化对CO2的适应并导致微囊藻种群发生演替的影响机制。研究结果不仅从个体和种群层面揭示CO2变化可能诱导蓝藻发生进化适应，引起蓝藻水华种类和基因型组成发生改变，而且也为阐明全球变化对蓝藻水华发生及演替的影响提供重要依据。

CO2-浓缩机制(CCM)是蓝藻适应低浓度二氧化碳环境下进化出的一种特殊的碳固定机制。然而，人为活动导致的CO2等温室气体急剧增加是否影响蓝藻CCM有待进一步研究。项目从常见的水华蓝藻-微囊藻CCM基因着手，研究了微囊藻CCM不同组分CO2 吸收系统和碳酸氢盐吸收系统多样性，发现了微囊藻CO2 吸收系统具有较高的保守性，但碳酸氢盐吸收系统分化出sbtA和bicA两种类型，且基因型与表型无直接关联。在此基础上，进一步研究了2种基因型类型对不同CO2浓度的响应及竞争特征，结果表明sbtA基因型微囊藻在低CO2浓度(200ppm)条件下的生长、光合等显著高于bicA基因型微囊藻，而在高CO2浓度(800ppm)条件下sbtA基因型微囊藻生长、光合等显著低于bicA基因型微囊藻。当两种基因型微囊藻在CO2浓度为200 ppm、400ppm和800ppm条件下混合培养15天后，在低CO2浓度(200ppm)下sbtA基因型生物量是bicA基因型的3.5-6.2倍，在高CO2浓度(800ppm)条件下bicA基因型生物量是sbtA基因型的3.0-3.5倍，而在CO2浓度为400ppm时两种基因型均可能成为优势，并存在藻株差异。通过对滇池、三峡库区支流水库采样分析，发现了SbtA基因型微囊藻在各样点中始终占据绝对优势，相对丰度远远高于bicA基因型微囊藻，但是不同CCM基因型存在着演替和样点的差异。这些结果说明了不同CCM基因型在不同CO2浓度环境中存在着竞争效应，随着环境CO2的变化，微囊藻CCM发生了微进化，形成了不同CCM基因型来适应水体CO2浓度变化，进而使得微囊藻种群得以维持，并在不同条件CO2条件下微囊藻能够长期保持优势，形成水华。