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Underwater marine life: coupling photosynthesis and respiration

Researchers from the CEA-IRTSV and their partners have revised our understanding of the cellular mechanisms behind the impressive photosynthetic capacity of the unicellular marine organisms known as diatoms. The scientists discovered an unexpected interaction between photosynthesis and respiration, which could inspire promising developments in biotechnology.

Published on 16 July 2015

Whereas terrestrial plants provide photosynthetic activity on land, in the oceans photosynthesis is performed by microscopic unicellular organisms known as phytoplankton. Dominating this community, diatoms (comprising thousands of marine species) are at the origin of the food chain in these environments. They capture and sequester atmospheric CO2 in the depths, and provide about 20% of the planetary photosynthesis. How were diatoms able to reach this level and dominate the phytoplankton community?
As part of an international collaboration (including Belgium, France, the USA and Italy), a French team involving the CEA-IRTSV, CNRS, INRA, INSERM, the Ecole Normale Supérieure, the universities of Joseph Fourier, Paris-Sud, and Pierre et Marie Curie, and the Fermentalg company has decrypted the characteristics of the photosynthetic process in diatoms at the molecular level.

Decrypting the photosynthetic mechanism of diatoms
The fixation of CO2 by photosynthesis requires the production of energy (ATP molecules) and reducing power (NADPH molecules) in the chloroplast, and in well-defined proportions. In diatoms, the molecular mechanisms that work to manage the ATP/NADPH ratio occur through ongoing exchanges between the chloroplast and the mitochondrion (the cellular compartment dedicated to respiration). This process, which helps to optimize photosynthesis, has certainly contributed to the ecological success of diatoms in the world's oceans.

The discovery of this coupling mechanism between photosynthesis and respiration in diatoms makes it possible to imagine unprecedented biotechnological applications, such as increasing the production of biomass to produce molecules of interest, by acting on the simultaneous use of light (for photosynthesis) and carbon sources (for respiration).

Representation of a diatom and the cellular mechanisms coupling photosynthesis and respiration in this organism. The chloroplast, which produces ATP and NADPH using light, is joined to the mitochondrion, the headquarters of cellular respiration. The two cellular compartments can thus exchange the ATP and NADPH molecules that they produce, optimizing the fixation of carbon in diatoms. © IBENS CNRS-ENS

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