%0 Generic %D 2023 %T Population dynamics of the cosmopolitan eukaryotic picophytoplankton Bathycoccus during seasonal blooms in the bay of Banyuls sur Mer (North Western Mediterranean sea) %A Devic, Martine %A Mariac, Cédric %A Vergé, Valérie %A Schatt, Philipe %A Dennu, Louis %A Lozano, Jean-Claude %A Bouget, François-Yves %A Sabot, François %K RCC1613 %K RCC1615 %K RCC1868 %K RCC4222 %K RCC4752 %K RCC5417 %K RCC685 %X Abstract Although Bathycoccus is one of the most abundant picophytoplankton, little is known about the genetic diversity underlying its adaptation to ecological niches. In this study, the diversity of Bathycoccus populations during their annual bloom in the Mediterranean bay of Banyuls France was assessed by an INDEL based approach. Oxford Nanopore Technology (ONT) was used to characterise structural variants (SV) among the genomes of Bathycoccus sampled from geographically distinct regions in the world ocean. Markers derived from INDEL were validated by PCR and sequencing in the world-wide strains. These markers were then used to genotype 55 Bathycoccus strains isolated during the winter bloom 2018-2019 in Banyuls. With five markers, eight Multi Loci Genotypes (MLG) were determined, two of which represented 53% and 29% of the isolates. Physiological studies confirmed that isolates are phenotypically different, cells isolated in February growing better at low temperature than those isolated in December. When tested on environmental samples, two diversity markers showed a similar allele frequency in sea water as in individual Bathycoccus strains isolated at the same period. We conclude that these markers constitute a resource to identify the most abundant variant alleles in a given bloom. A follow-up on three consecutive blooms revealed differences in allele abundance during the course of a bloom, particularly at initiation, and between years. In addition to Bathycoccus prasinos , two other species of Bathycoccus were identified including the recently described species B. calidus and a novel species B. catiminus , suggesting that species diversity of the genus Bathycoccus may be underestimated. %I BioRxiv %G eng %U http://biorxiv.org/lookup/doi/10.1101/2023.02.09.527951 %9 preprint %R 10.1101/2023.02.09.527951