Dynamic changes of genotypes of <i>Microcystis</i> CO₂-concentration mechanism and their competitive effects on CO₂

Abstract

由于具有高效的CO₂-浓缩机制,蓝藻在低CO₂浓度条件下具有竞争优势。然而,随着大气中CO₂浓度急剧增加,蓝藻CO₂-浓缩机制如何响应的研究较少。因此,本文以常见水华蓝藻——微囊藻为研究对象,通过对滇池微囊藻水华动态及不同CO₂-浓缩机制基因型进行监测,探讨蓝藻CO₂-浓缩机制基因的微进化特征及其动态变化。同时,设置高(0.08%)、中(0.04%)、低(0.02%)CO₂浓度(V/V)进一步揭示微囊藻不同CO₂-浓缩机制基因微进化对CO₂的竞争效应。结果表明:滇池无机碳浓度在4个采样点存在空间差异性,均呈现先降低后升高的趋势,并以HCO^-₃为主要无机碳存在形式。调查期间,东大河、观音山、洛龙河和生态所4个采样点的微囊藻均以sbtA基因型占绝对优势,相对丰度远高于bicA基因型。在不同水华时期,bicA基因型和sbtA基因型呈现相反的变化趋势,即从水华前期到水华中期,sbtA基因型的相对丰度逐渐升高,而到水华后期,出现bicA基因型增多的现象。室内竞争实验同样表明高浓度CO₂培养环境下,bicA基因型具有明显竞争优势,随CO₂浓度的降低,呈现bicA基因型向sbtA基因型转变的趋势。这些结果表明水华中期无机碳浓度相对较低,能适应碳限制环境的sbtA基因型的微囊藻表现出竞争优势,而对CO₂浓度变化敏感的bicA基因型的微囊藻随无机碳浓度的升高逐渐增多;同时,在总碱度,pH和Chl.a影响下,微囊藻基因型在滇池不同微囊藻水华期呈现bicA→sbtA→bicA转变。这些结果说明微囊藻能通过调节不同CO₂-浓缩机制基因藻株响应水体无机碳浓度,保持种群竞争优势,并维持水华的形成。;The highly efficient CO₂ concentration mechanism (CCM) gives cyanobacteria a competitive advantage under low CO₂ conditions. However, with the rapid increase in atmospheric CO₂ concentration, little information has been presented on how the CO₂ concentration mechanism of cyanobacteria responds. Therefore, this study takes a common blooming cyanobacterium, Microcystis, to investigate in the present by monitoring the dynamic changes and different CCM genotypes of Microcystis in Lake Dianchi. At the same time, the microevolutionary characteristics and dynamic changes of CCM genotypes in Microcystis were also discussed. Furthermore, the competing effects of different CCM genotypes in Microcystis at high (0.08%), medium (0.04%) and low (0.02%) CO₂ concentrations (V/V) were compared. The results showed that the concentration of inorganic carbon (IC) in Lake Dianchi was spatially variable at four sampling sites, but all sites showed a trend of first decreasing and then increasing IC concentrations, and HCO^-₃ was the major form of IC. At the four sampling sites of DDH, GYS, LLH and STS, the sbtA genotype Microcystis was dominant and its relative abundance was much higher than that of the bicA genotype Microcystis. In different bloom periods, the bicA and sbtA genotypes of Microcystis showed opposite trends, i.e. the relative abundance of the sbtA genotype Microcystis gradually increased from early to mid- bloom, while the bicA genotype Microcystis increased only in late bloom. The competition experiments showed that the bicA genotype had an apparent competitive advantage in a high CO₂ environment and showed a trend of transition from the bicA genotype to the sbtA genotype with decreasing CO₂ concentration. These indicate that the IC concentration was relatively low in the middle of the bloom period, resulting in the sbtA genotype showing a competitive advantage in a carbon-limited environment, while the bicA genotype, a sensitive type to changing CO₂ concentration, gradually increased with increasing IC concentration. In addition, the genotypes of Microcystis showed a bicA→sbtA→bicA transition during different Microcystis bloom periods in Lake Dianchi due to the effects of total alkalinity, pH and Chl.a. These results suggest that Microcystis can maintain its competitive advantage and sustain the bloom by regulating the algal strains with different CCM genotypes in response to the IC concentration in the water.