Olga Carnicer

Dalhousie University, Oceanography, Post-Doc

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Post-doctoral fellow in Dalhousie University, Canada working on dinoflagellates macromolecular content.
Address: Quito, Provincia de Pichincha, Ecuador

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Elemental and macromolecular composition of three species of Chloropicophyceae

Elemental and macromolecular composition of three species of Chloropicophyceae grown under non-li... more Elemental and macromolecular composition of three species of Chloropicophyceae grown under non-limiting (t=0) and nitrogen starvation conditions(t>0). To achieve N-starvation, cultures in balanced growth (t=0) were transferred into N-free media and monitor over time.<br>For more details see Ebenezer et al (2021) doi 10.1002/lno.12013<br>

Elemental and macromolecular composition of the marine Chloropicophyceae, a major group of oceanic photosynthetic picoeukaryotes

Limnology and Oceanography, 2022

Chloropicophyceae (Prasinophyte Clade VII) are small nonmotile coccoid cells with cell diameters ... more Chloropicophyceae (Prasinophyte Clade VII) are small nonmotile coccoid cells with cell diameters ranging from 1 to 3 μm. Molecular surveys indicate they are relatively high in abundance in moderately oligotrophic oceanic waters and may substantively contribute to biogeochemical cycling in the sea. Here, we quantify the elemental and macromolecular composition of three subtropical Chloropicophyceae strains: Chloropicon mariensis, Chloropicon maureeniae, and Chloropicon roscoffensis under nutrient-sufficient exponential growth and nitrate starvation. Under nutrient-sufficient conditions the Chloropicophyceae are high in C : N and quite low in C : P and N : P relative to the canonical Redfield ratio, reflecting their relatively high nucleic acid composition compared to many other phytoplankton taxa. Nitrate starvation causes increases in C : N and C : P and decreases in N : P, primarily due to increases in carbohydrate and lipid and decreases in protein and RNA. There is genetic evidence that unlike most other green algae, Chloropicophyceae are diploid. The high nucleic acid content in the Chloropicon is consistent with the hypothesis that the nucleus, as a nonscalable component, takes up a larger and substantial proportion of cell mass in diploid picoeukaryotes. The elemental and macromolecular composition of these Chloropicophyceae, and relatively homeostatic response to N-starvation compared to diatoms, provides some insight into their success in the moderately oligotrophic ocean. Photosynthetic picoeukaryotes, characterized by a cell diameter between 0.2 and 3 μm, are common in the sea surface (Worden and Not 2008; Freitas et al. 2020) and often contribute substantively to primary productivity in moderately oligotrophic regions (Not et al. 2004; Lepére et al. 2009; Massana et al. 2011). Chlorophyta are common constituents of marine photosynthetic picoeukaryotes communities (Simmons et al. 2016; Tragin and Vaulot 2019). Micromonas, Bathycoccus, and Ostreococcus, class Mamiellophyceae, tend to be most abundant in the coastal regions (Not et al. 2004; Karlusich et al. 2020), although they can also be found in open ocean regions (Joli et al. 2017; Leconte et al. 2020). By contrast, the relatively newly described class Chloropicophyceae (Prasinophyte Clade VII) tend to be the more dominant Chlorophyta in moderately oligotrphic waters (Lopes dos Santos et al. 2016, 2017a,b; Karlusich et al. 2020). Based on metabarcode data from the Tara expedition, the Chlorophyta sequences constitute an average of 16-20% of the photosynthetic sequences in the sea surface and deep chlorophyll maximum in the 0.8-5 μm size fraction (Lopes dos Santos et al. 2017a; Carradec et al. 2018). The Chloropicophyceae represent a majority of the Chlorophyta sequences in these samples, up to a maximum of 99.9% (Lopes dos Santos et al. 2017a). Chloropicophyceae are nonmotile coccoid cells, mostly 1.5-3 μm in diameter, have a single nucleus, mitochondria, and chloroplast with a starch grain, and a suite of carotenoids that includes violaxanthin, lutein, astaxanthin or antheraxanthin, but lack prasinoxanthin which is present in several other small marine green phytoplankton taxa including Ostreococcus (Lopes dos Santos et al. 2017a). The Chloropicophyceae have been divided into 10 clades (A1-A7, B1-B3) and two genera: Chloropicon (Clade A) and Chloroparvula (Clade B) (Lopes dos Santos et al. 2017b). Few morphological or ultrastructural

Olga Carnicer

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