Diversity of cultured photosynthetic flagellates in the northeast Pacific and Arctic Oceans in summer

[摘要] During the MALINA cruise (summer 2009), an extensive effort was undertaken toisolate phytoplankton strains from the northeast (NE) Pacific Ocean, theBering Strait, the Chukchi Sea, and the Beaufort Sea. In order tocharacterise the main photosynthetic microorganisms occurring in the Arcticduring the summer season, strains were isolated by flow cytometry sorting(FCS) and single cell pipetting before or after phytoplankton enrichment ofseawater samples. Strains were isolated both onboard and back in thelaboratory and cultured at 4 °C under light/dark conditions. Overall, weisolated and characterised by light microscopy and 18 S rRNA gene sequencing104 strains of photosynthetic flagellates which grouped into 21 genotypes(defined by 99.5% 18 S rRNA gene sequence similarity), mainly affiliated toChlorophyta and Heterokontophyta. The taxon most frequently isolated was anArctic ecotype of the green algal genus Micromonas (Arctic Micromonas), which was nearly the onlyphytoplankter recovered within the picoplankton (< 2 μm) size range.Strains of Arctic Micromonas as well as other strains from the same class(Mamiellophyceae) were identified in further detail by sequencing theinternal transcribed spacer (ITS) region of the rRNA operon. The MALINAMicromonas strains share identical 18 S rRNA and ITS sequences suggesting high genetichomogeneity within Arctic Micromonas. Three other Mamiellophyceae strains likelybelong to a new genus. Other green algae from the genera Nephroselmis, Chlamydomonas, and Pyramimonas were alsoisolated, whereas Heterokontophyta included some unidentified Pelagophyceae,Dictyochophyceae (Pedinellales), and Chrysophyceae (Dinobryon faculiferum). Moreover, we isolatedsome Cryptophyceae (Rhodomonas sp.) as well as a few Prymnesiophyceae anddinoflagellates. We identified the dinoflagellate Woloszynskia cincta by scanning electronmicroscopy (SEM) and 28 S rRNA gene sequencing. Our morphological analysesshow that this species possess the diagnostic features of the genusBiecheleria, and the 28 S rRNA gene topology corroborates this affiliation. We thuspropose the transfer of W. cincta to the genus Biecheleria and its recombination as Biecheleria cincta.

[学科分类] 地球化学与岩石