The Transition Toward Nitrogen Deprivation in Diatoms Requires Chloroplast Stand-By and Deep Metabolic Reshuffling.

Matteo Scarsini,Brigitte Veidl,Stanislas Thiriet-Rupert,Florence Mondeguer,Hanhua Hu,Justine Marchand,Benoît Schoefs

doi:10.3389/fpls.2021.760516

Abstract

Microalgae have adapted to face abiotic stresses by accumulating energy storage molecules such as lipids, which are also of interest to industries. Unfortunately, the impairment in cell division during the accumulation of these molecules constitutes a major bottleneck for the development of efficient microalgae-based biotechnology processes. To address the bottleneck, a multidisciplinary approach was used to study the mechanisms involved in the transition from nitrogen repletion to nitrogen starvation conditions in the marine diatom Phaeodactylum tricornutum that was cultured in a turbidostat. Combining data demonstrate that the different steps of nitrogen deficiency clustered together in a single state in which cells are in equilibrium with their environment. The switch between the nitrogen-replete and the nitrogen-deficient equilibrium is driven by intracellular nitrogen availability. The switch induces a major gene expression change, which is reflected in the reorientation of the carbon metabolism toward an energy storage mode while still operating as a metabolic flywheel. Although the photosynthetic activity is reduced, the chloroplast is kept in a stand-by mode allowing a fast resuming upon nitrogen repletion. Altogether, these results contribute to the understanding of the intricate response of diatoms under stress.

Highlights

IntroductionThe human population and cities size have risen. To sustain the continuous increase in the energy demand, fossil energies were massively used, becoming progressively limited
Since the industrial revolution, the human population and cities size have risen
The culture entered the transition phase, not at the onset of the Day from the Reduction of Nitrogen Supply (DRNS) but when the minimum N-ext availability is reached at 5 DNRS (0.03 mM NO−3 corresponding to 0.007 μmol NO−3 10−6 cells) (Figure 1B)

Summary

Introduction

The human population and cities size have risen. To sustain the continuous increase in the energy demand, fossil energies were massively used, becoming progressively limited. The large exploitation of plants for other purposes than food and feed production resulted in a counterproductive competition for Nitrogen Deprivation in Diatoms agricultural land use, rocking the inflation of food prices (Kazamia and Smith, 2014) Microalgae are another type of photosynthetic organisms that can be grown in open ponds or photobioreactors (i.e., farmland areas, avoiding the land competition) with the aim to use them as cell factories in production platforms (Gordon et al, 2019). Diatoms have always played a crucial role in the biosphere as they contribute to 20–40% of the oceanic biomass production and approximately 20% of the total carbon fixation (Benoiston et al, 2017; Falciatore et al, 2020) Their metabolic diversity and flexibility make them attractive organisms for a wide range of applications in diverse industrial and commercial fields, including biofuel production, nanotechnological applications, pigments and dietary lipids production (Mimouni et al, 2012)

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