Abstract
In diatoms, the main photosynthetic pigments are chlorophylls a and c, fucoxanthin, diadinoxanthin and diatoxanthin. The marine pennate diatom Haslea ostrearia has long been known for producing, in addition to these generic pigments, a water-soluble blue pigment, marennine. This pigment, responsible for the greening of oysters in western France, presents different biological activities: allelopathic, antioxidant, antibacterial, antiviral, and growth-inhibiting. A method to extract and purify marennine has been developed, but its chemical structure could hitherto not be resolved. For decades, H. ostrearia was the only organism known to produce marennine, and can be found worldwide. Our knowledge about H. ostrearia-like diatom biodiversity has recently been extended with the discovery of several new species of blue diatoms, the recently described H. karadagensis, H. silbo sp. inedit. and H. provincialis sp. inedit. These blue diatoms produce different marennine-like pigments, which belong to the same chemical family and present similar biological activities. Aside from being a potential source of natural blue pigments, H. ostrearia-like diatoms thus present a commercial potential for aquaculture, cosmetics, food and health industries.
Highlights
Seas and oceans cover more than 70% of the Earth’s surface; water mainly transmits and scatters blue wavelengths while absorbing the red part of the solar light spectrum, leading astronauts to say our planet is blue
From what can be seen in simple 1H nuclear magnetic resonance (NMR) spectra, the difference between the two extracellular forms appears smaller than the difference between extracellular marennine (EMn) and intracellular marennine (IMn) of H. ostrearia
These preliminary results appeal for a more thorough study of the marennine-like pigments produced by the different species of blue diatoms, which constitute an original family of natural blue pigments
Summary
Seas and oceans cover more than 70% of the Earth’s surface; water mainly transmits and scatters blue wavelengths while absorbing the red part of the solar light spectrum, leading astronauts to say our planet is blue. Known as ―blue algae‖, cyanobacteria have specific accessory protein–pigment complexes, the phycobiliproteins Some of these phycobiliproteins, like phycocyanin and allophycocyanin, have a blue color due to their absorption of orange and/or red light [11]. Phycocyanin and allophycocyanin are not restricted to cyanobacteria, as they have been evidenced in two groups of photosynthetic eukaryotes, Rhodophyta and Glaucophyta Members of another group, the Cryptophyta, contain only one of these two blue pigments, phycocyanin (e.g., [17]). More than ten conjugated double bonds are necessary to reduce the energy gap to absorb red light [20] so that the molecule appears blue, and this is a rather rare constellation. At least one of the blue pigments produced by these new species (H. karadagensis) is different from marennine, but all belong to the same chemical family.
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