Phytoplankton, such as diatoms, experience great variations of photon flux density (PFD) and light spectrum along the marine water column. Diatoms have developed some rapidly-regulated photoprotective mechanisms, such as the xanthophyll cycle activation (XC) and the non-photochemical chlorophyll fluorescence quenching (NPQ), to protect themselves from photooxidative damages caused by excess PFD. In this study, we investigate the role of blue fluence rate in combination with red radiation in shaping photoacclimative and protective responses in the coastal diatom Pseudo-nitzschia multistriata. This diatom was acclimated to four spectral light conditions (blue, red, blue-red, blue-red-green), each of them provided with low and high PFD. Our results reveal that the increase in the XC pool size and the amplitude of NPQ is determined by the blue fluence rate experienced by cells, while cells require sensing red radiation to allow the development of these processes. Variations in the light spectrum and in the blue versus red radiation modulate either the photoprotective capacity, such as the activation of the diadinoxanthin-diatoxanthin xanthophyll cycle, the diadinoxanthin de-epoxidation rate and the capacity of non-photochemical quenching, or the pigment composition of this diatom. We propose that spectral composition of light has a key role on the ability of diatoms to finely balance light harvesting and photoprotective capacity.

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In this review, we aim to explore the potential of microalgal biodiversity and ecology for biotechnological use. A deeper exploration of the biodiversity richness and ecophysiological properties of microalgae is crucial for enhancing their use for applicative purposes. After describing the actual biotechnological use of microalgae, we consider the multiple faces of taxonomical, morphological, functional and ecophysiological biodiversity of these organisms, and investigate how these properties could better serve the biotechnological field. Lastly, we propose new approaches to enhancing microalgal growth, photosynthesis, and synthesis of valuable products used in biotechnological fields, mainly focusing on culture conditions, especially light manipulations and genetic modifications.

Microalgal growth maximization is becoming a duty for enhancing the biotechnological fate of these photosynthetic microorganisms. This study, based on an extensive set of data, aims to revisit diatom’s cultivation in laboratory with the objective to increase growth rate and biomass production. We investigated the growth ability and resource requirements of the coastal diatom Skeletonema marinoi Sarno & Zingone grown in laboratory in the conventional f/2 medium with aeration and in two modified conditions: (i) the same medium with water movement inside and (ii) an enriched medium with the same water movement. Results revealed that, by doubling the concentration of phosphate, silicate, microelements and vitamins, growth rate was successfully enhanced, preventing phosphate or silicate limitation in the f/2 culture medium. Yet, irrespective of the media (f/2 or enriched one), water movement induced an increase of growth efficiency compared to aeration, affecting nutrients’ requirement and consumption by diatoms. This study is an important step for enhancing diatom biomass production, reducing its cost, as required in the blue biotechnology context.

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