A Day in the Life of Microcystis aeruginosa Strain PCC 7806 as Revealed by a Transcriptomic Analysis

The cyanobacterium, Microcystis aeruginosa, is able to proliferate in a wide range of freshwater ecosystems and to produce many secondary metabolites that are a threat to human and animal health. The dynamic of this production and more globally the metabolism of this species is still poorly known. A DNA microarray based on the genome of M. aeruginosa PCC 7806 was constructed and used to study the dynamics of gene expression in this cyanobacterium during the light/dark cycle, because light is a critical factor for this species, like for other photosynthetic microorganisms. This first application of transcriptomics to a Microcystis species has revealed that more than 25% of the genes displayed significant changes in their transcript abundance during the light/dark cycle and in particular during the dark/light transition. The metabolism of M. aeruginosa is compartmentalized between the light period, during which carbon uptake, photosynthesis and the reductive pentose phosphate pathway lead to the synthesis of glycogen, and the dark period, during which glycogen degradation, the oxidative pentose phosphate pathway, the TCA branched pathway and ammonium uptake promote amino acid biosynthesis. We also show that the biosynthesis of secondary metabolites, such as microcystins, aeruginosin and cyanopeptolin, occur essentially during the light period, suggesting that these metabolites may interact with the diurnal part of the central metabolism.铜绿微囊藻（Microcystis aeruginosa）是一类可在多种淡水生态系统中增殖的蓝细菌，其产生的多种次级代谢产物会对人类与动物健康构成威胁。目前，该物种次级代谢产物的合成动态乃至整体代谢机制仍鲜为人知。 本研究基于铜绿微囊藻PCC 7806的基因组构建了DNA微阵列（DNA microarray），并利用该芯片探究该蓝细菌在光暗周期下的基因表达动态——鉴于光照与其他光合微生物一样，是该物种生存的关键调控因子。这项首次将转录组学（transcriptomics）应用于微囊藻属物种的研究发现，超过25%的基因在光暗周期中，尤其是在暗-光过渡阶段，其转录本丰度发生了显著变化。 铜绿微囊藻的代谢呈现出明显的光暗时段分区特征：光照期内，碳摄取、光合作用与还原型磷酸戊糖途径共同推动糖原合成；而暗期则通过糖原降解、氧化型磷酸戊糖途径、三羧酸（TCA）支路代谢以及铵摄取来促进氨基酸生物合成。本研究同时证实，微囊藻毒素（microcystins）、铜绿肽素（aeruginosin）与蓝藻肽素（cyanopeptolin）等次级代谢产物的生物合成主要发生在光照期，这表明此类代谢产物或与中心代谢的昼夜调控通路存在相互作用。