Abstract
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.
Highlights
Microcystis aeruginosa is one of the most common bloom-forming cyanobacteria in freshwater ecosystems, and is widely distributed on the five continents
M. aeruginosa cells are organized in colonies, which carry out daily vertical migrations in the water column [6]
For 258 genes, data were only available at certain time sampling points, whereas a complete time series data was obtained for 4757 genes
Summary
Microcystis aeruginosa is one of the most common bloom-forming cyanobacteria in freshwater ecosystems, and is widely distributed on the five continents. Members of this genus are known to be able to synthesize numerous secondary metabolites, including microcystins, which are hepatotoxins frequently involved in animal and human poisoning [1,2]. The first is a benthic phase, during which it lives on sediment during the Winter and the early Spring, and the second a planktonic phase, during which it lives in the water column during Summer and Autumn [5] During this second phase, M. aeruginosa cells are organized in colonies, which carry out daily vertical migrations in the water column [6]. The light exposure of M. aeruginosa cells can be very limited due to these vertical migrations and to low light levels in the water column when high cyanobacterial biomass reduces water transparency
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