What Was Old Is New Again: The Pennate Diatom Haslea ostrearia (Gaillon) Simonsen in the Multi-Omic Age

Abstract

The marine pennate diatom Haslea ostrearia has long been known for its characteristic blue pigment marennine, which is responsible for the greening of invertebrate gills, a natural phenomenon of great importance for the oyster industry. For two centuries, this taxon was considered unique; however, the recent description of a new blue Haslea species revealed unsuspected biodiversity. Marennine-like pigments are natural blue dyes that display various biological activities—e.g., antibacterial, antioxidant and antiproliferative—with a great potential for applications in the food, feed, cosmetic and health industries. Regarding fundamental prospects, researchers use model organisms as standards to study cellular and physiological processes in other organisms, and there is a growing and crucial need for more, new and unconventional model organisms to better correspond to the diversity of the tree of life. The present work, thus, advocates for establishing H. ostrearia as a new model organism by presenting its pros and cons—i.e., the interesting aspects of this peculiar diatom (representative of benthic-epiphytic phytoplankton, with original behavior and chemodiversity, controlled sexual reproduction, fundamental and applied-oriented importance, reference genome, and transcriptome will soon be available); it will also present the difficulties encountered before this becomes a reality as it is for other diatom models (the genetics of the species in its infancy, the transformation feasibility to be explored, the routine methods needed to cryopreserve strains of interest).

DNA methylation is linked to the monoallelic expression ofMRP3, a diatom mating type determining gene

“…In diatoms, the percentage of methylated cytosines varies markedly, with levels similar to what we found in P. multistriata (8.63% in Fragilariopsis cylindrus, Huff & Zilberman, 2014) but also much smaller (2.57% in Thalassiosira pseudonana (Huff & Zilberman, 2014) and 2.67% in Haslea ostrearia (Gabed et al, 2022)) or tremendously higher as for Cyclotella cryptica in which up to ~60% methylation was found (Traller et al, 2016). In agreement with what was found in other diatoms (Huff & Zilberman, 2014Traller et al, 2016Veluchamy et al, 2013, Gabed et al, 2022, most of the methylation was found in CG context while the global methylation level in CHG and CHH contexts was below 1% in all analyzed samples (Fig 2A, Table S2). About 70% of methylated CpGs were located within repeat regions, while we found only 0.8% in TSS and 0.7% in TTS (Fig 2B), and between 1 and 1.5% in genes, where some genes were found to be highly methylated.…”

“…DNA methylation has previously been investigated in diatoms ( Huff & Zilberman, 2014; Traller et al, 2016; Veluchamy et al, 2013, Gabed et al, 2022, Hoguin et al, 2023 ), revealing the conservation of most of the enzymes required for the epigenetic machinery and confirming a major role of this process in the silencing of transposable elements (TEs).…”

The reproducibility of the bacterial community present in the cultures of the marine diatom Haslea ostrearia

“…H. ostrearia is a microalga complex to grow under laboratory conditions, and even after years of development, it is still a challenge to propose a protocol that allows it to grow without any bacteria [12,13,14]. Indeed, the tests previously performed in our laboratory showed that, even with all the nutrients needed, a high amount of antibiotics or a long exposure to them tended to kill the microalgae culture itself.…”