CYanobacterial toxin production and Photoprotection processes in a changing EnviRonment (CYPHER) – CYPHER

Cyanobacteria are present in a large range of habitats and climates, including extreme conditions going from deserts to arctic lakes. They are equipped with all the physiological mechanisms needed to survive to extreme and fluctuating environments allowing them to be the predominant species in ecosystems under specific environmental conditions. Under certain conditions, a sudden and rapid growth of one or some cyanobacterial species is induced leading to blooms. There is a direct relationship between the frequency of cyanobacterial blooms and the augmentation of available nutritive resources caused by human activities. Climate changes also favor the appearance of cyanobacteria blooms suggesting that this phenomenon will be amplified in the future. The cyanobacterial blooms disrupt the functioning of the continental aquatic ecosystems with serious consequences for the production of drinking water, or recreational aquatic activities. These disturbances are largely connected to the capacity of some cyanobacteria to synthesize toxins hazardous for human and animal health. Among them, the microcystins (MCs) are the most common as they are produced by the most common bloom-forming species Microcystis and Planktothrix (cHAB: cyanobacterial Harmful Algal Bloom). The concentration of toxins present in each bloom varies. Indeed, for a toxic species, only some strains present in the bloom synthesize toxins, and in addition, in these toxic cells, toxin biosynthesis depends on environmental conditions. Thus, despite that the survey of cyanobacterial cells and toxins is one request of safety agencies in Europe and France, it is impossible to predict the concentration of toxins only from biomass data. This impossibility of prediction represents big costs for the water end-users and a health risk for populations. For this reason, it becomes urgent to understand the determinism of the toxin production during the blooms and one way to achieve this goal is to found what are the factors regulating toxin synthesis and to elucidate the functional role of toxins.
Several stress conditions increases cyanotoxin synthesis but it is not clear if there is a direct effect of stress factors or an indirect effect via photosynthesis and/or photoprotection. It is also not clear, why cyanotoxin producers are more resistant to stress. Is it a direct effect of the toxin or a photoprotective mechanism up-regulated by their presence? Thus, it is crucial for the understanding of cHAB to examine the fluctuation of toxic cyanobacterial sub-populations and toxin synthesis in relationship with the rates of photosynthesis and protection mechanisms in strains isolated from natural environment and usually present in blooms. This is the main objective of CYPHER. We will study the connection between microcystin synthesis and the cellular redox changes generated by variations in photosynthesis and in photoprotective mechanisms in MCs producer Planktothrix presenting different phenotypes and living in different ecosystems. We will also study the possible role of toxins on photosynthesis and photoprotective mechanisms under stress conditions. The originality of our proposition is to put together experts in: ecology, toxin synthesis, toxin modification and transcriptomics (partner 1), comparative genomics and secondary metabolites (partners 2) and cellular photosynthesis and photoprotective mechanisms (partner 3) to do a study that should help further predict the concentration of cyanotoxin producing strains in blooms generated by different environmental conditions, especially associated with a changing climate and a more polluted world. Thus, the expected fundamental knowledge will help ecological scientists or end-users in the large application on quality and surveys of water plans.