Abstract
Diatoms adapt to changing environmental conditions in very efficient ways. Among the mechanisms that can be activated, the reorientation of carbon metabolism is crucial because it allows the storage of energy into energy-dense molecules, typically lipids. Beside their roles in physiology, lipids are commercially interesting compounds. Therefore studies dealing with this topic are relevant for both basic and applied science. Although the molecular mechanisms involved in the reorientation of carbon metabolism as a response to a deficiency in nutrients such as nitrogen or phosphorus has been partially elucidated, the impacts of carbon availability on the implementation of the reorientation mechanisms remain unclear. Indeed, it has not been determined if the same types of mechanisms are activated under carbon and other nutrient deficiencies or limitations. The first aim of this work was to get insights into the physiological, biological and molecular processes triggered by progressive carbon starvation in the model diatom Phaeodactylum tricornutum. The second aim was to investigate the effects of the growth light intensity on these processes. For such a purpose three different photon flux densities 30, 300, and 1000 μmol photons m-2 s-1 were used. The results presented here demonstrate that under carbon limitation, diatom cells still reorient carbon metabolism toward either phosphoenolpyruvate or pyruvate, which serves as a hub for the production of more complex molecules. The distribution of carbon atoms between the different pathways was partially affected by the growth photon flux density because low light (LL) provides conditions for the accumulation of chrysolaminarin, while medium light mostly stimulated lipid synthesis. A significant increase in the amount of proteins was observed under high light (HL).
Highlights
Diatoms constitute the most abundant group of marine eukaryotic organisms with more than 200 genera and approximately 100,000 species and most have still to be discovered (e.g., Heydarizadeh et al, 2014; Bork et al, 2015; Vinayak et al, 2015; Beauger et al, 2019)
We have compared the impacts of the growth photon flux densities on the reorientation of the carbon metabolism of P. tricornutum grown under progressive CO2 limitation with the aim to highlight how the partitioning of carbon among its potential sinks is impacted
Our results show that the impact of light intensity on cell development, physiology and gene regulation of P. tricornutum depends on growth phase, i.e., the cell’s physiological state
Summary
Diatoms constitute the most abundant group of marine eukaryotic organisms with more than 200 genera and approximately 100,000 species and most have still to be discovered (e.g., Heydarizadeh et al, 2014; Bork et al, 2015; Vinayak et al, 2015; Beauger et al, 2019). Excessive or insufficient incident photon flux density constrains diatom optimal performance in terms of biomass and metabolite composition (Goldman, 1980; Vidoudez and Pohnert, 2008; Barofsky et al, 2009, 2010; Carvalho et al, 2011). These metabolites are generated along a network of biochemical pathways, the core of which being occupied by the central carbon metabolism. Many stress conditions result in the reorientation of the carbon metabolism toward the accumulation of energy-dense molecules such as lipids (for reviews, see Sayanova et al, 2017; Zulu et al, 2018). It seems that CO2-limitation could be a limiting factor for the development of an efficient algal biotechnological process as it is already for algae living in the natural environment
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