Director of studies: Dr. Marina Montresor
Department of Integrative Marine Ecology
The formation of resting stages – i.e. stages capable to enter a reversible stage of reduced metabolic activity, or "dormancy" - is widespread amongst all organisms spanning from bacteria, to protists, animals and plants. This life cycle trait allows organisms to cope with environmental conditions sub-optimal for growth, seasonality of food availability and plays a fundamental role in shaping population dynamics. Resting stages form "seed banks" in marine sediments, where they can survive for long time, and subsequently germinate bringing back to the water column actively growing cells/organisms. The formation and germination of dormant stages is linked to the perception of external cues, whose mechanisms have been elucidated for higher plants and animals and partly for bacteria. However, information on these processes in marine microalgae is still limited.
The main objective of the project is to investigate the factors that trigger the formation and germination of spores in diatoms. Diatom spores are formed by subsequent mitotic divisions in which the highly silicified thecae are synthesized. Target species will be one species of the genus Chaetoceros and Leptocylindrus danicus, in which spore formation is linked to the sexual phase. Laboratory experiments suggest that spore formation is induced by nutrient starvation but field observations do not entirely support this observation. A detailed experimental set up in which e.g. both the external and internal nitrogen pools have been measured are however lacking. The main cue for spore germination is exposure to light. However, also on this aspect the information available is limited.
The backbone of the project will focus on the role of nutrient (nitrogen) concentration in inducing the formation of spores and on the role of light (both as quality and quantity) in inducing the germination of resting stages. The project will also include transcriptomic approaches on key time points/phases of the life cycle transitions to gain insights on the molecular mechanisms involved in the perception of the cues and in the physiological response.
The results of the project have ecological (insights on the cues triggering two key life phase transitions that have implications for e.g. bloom termination, inoculum of the water column upon germination, species succession), applicative (induction of spore formation may represent as a way to preserve strains over time) and evolutionary implications. Moreover, the molecular results will be important for the interpretation of meta-transcriptomic data gained in situ.
