The world's oceans represent by far the largest biome, with great importance for the global ecosystem [1-4]. The vast majority of ocean biomass and biodiversity is composed of microscopic plankton. Recent results from the Tara Oceans metabarcoding study revealed that a significant part of the plankton in the upper sunlit layer of the ocean is represented by an understudied group of heterotrophic excavate flagellates called diplonemids [5, 6]. We have analyzed the diversity and distribution patterns of diplonemid populations on the extended set of Tara Oceans V9 18S rDNA metabarcodes amplified from 850 size- fractionated plankton communities sampled across 123 globally distributed locations, for the first time also including samples from the mesopelagic zone, which spans the depth from about 200 to 1,000 meters. Diplonemids separate into four major clades, with the vast majority falling into the deep-sea pelagic diplonemid clade. Remarkably, diversity of this clade inferred from metabarcoding data surpasses even that of dinoflagellates, metazoans, and rhizarians, qualifying diplonemids as possibly the most diverse group of marine planktonic eukaryotes. Diplonemids display strong vertical separation between the photic and mesopelagic layers, with the majority of their relative abundance and diversity occurring in deeper waters. Globally, diplonemids display no apparent biogeographic structuring, with a few hyperabundant cosmopolitan operational taxonomic units (OTUs) dominating their communities. Our results suggest that the planktonic diplonemids are among the key heterotrophic players in the largest ecosystem of our biosphere, yet their roles in this ecosystem remain unknown.

• MeSH
• biodiverzita * MeSH
• ekosystém * MeSH
• Euglenozoa klasifikace   genetika   MeSH
• oceány a moře MeSH
• plankton klasifikace   genetika   MeSH
• RNA protozoální genetika   MeSH
• RNA ribozomální 18S genetika   MeSH
• sekvenční analýza RNA MeSH
• taxonomické DNA čárové kódování MeSH
• vodní organismy fyziologie   MeSH
• Publikační typ
• časopisecké články MeSH
• Geografické názvy
• oceány a moře MeSH

Kinetoplastid flagellates comprise basal mostly free-living bodonids and derived obligatory parasitic trypanosomatids, which belong to the best-studied protists. Due to their omnipresence in aquatic environments and soil, the bodonids are of ecological significance. Here, we present the first global survey of marine kinetoplastids and compare it with the strikingly different patterns of abundance and diversity in their sister clade, the diplonemids. Based on analysis of 18S rDNA V9 ribotypes obtained from 124 sites sampled during the Tara Oceans expedition, our results show generally low to moderate abundance and diversity of planktonic kinetoplastids. Although we have identified all major kinetoplastid lineages, 98% of kinetoplastid reads are represented by neobodonids, namely specimens of the Neobodo and Rhynchomonas genera, which make up 59% and 18% of all reads, respectively. Most kinetoplastids have small cell size (0.8-5 µm) and tend to be more abundant in the mesopelagic as compared to the euphotic zone. Some of the most abundant operational taxonomic units have distinct geographical distributions, and three novel putatively parasitic neobodonids were identified, along with their potential hosts.

• MeSH
• biodiverzita MeSH
• fylogeneze MeSH
• Kinetoplastida klasifikace   genetika   MeSH
• oceány a moře MeSH
• plankton genetika   MeSH
• ribozomální DNA genetika   MeSH
• RNA ribozomální 18S genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• oceány a moře MeSH

Microbial heliorhodopsins are a new type of rhodopsins, currently believed to engage in light sensing, with an opposite membrane topology compared to type-1 and type-2 rhodopsins. We determined heliorhodopsins presence/absence is monoderms and diderms representatives from the Tara Oceans and freshwater metagenomes as well as metagenome assembled genome collections. Heliorhodopsins are absent in diderms, confirming our previous observations in cultured Proteobacteria. We do not rule out the possibility that heliorhodopsins serve as light sensors. However, this does not easily explain their absence from diderms. Based on these observations, we speculate on the putative role of heliorhodopsins in light-driven transport of amphiphilic molecules.

• MeSH
• biologické modely MeSH
• gramnegativní bakterie klasifikace   genetika   MeSH
• metagenom MeSH
• mořská voda mikrobiologie   virologie   MeSH
• oceány a moře MeSH
• otevřené čtecí rámce MeSH
• senzorické rhodopsiny genetika   metabolismus   MeSH
• sladká voda mikrobiologie   virologie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• oceány a moře MeSH

Upon phosphorus (P) deficiency, marine phytoplankton reduce their requirements for P by replacing membrane phospholipids with alternative non-phosphorus lipids. It was very recently demonstrated that a SAR11 isolate also shares this capability when phosphate starved in culture. Yet, the extent to which this process occurs in other marine heterotrophic bacteria and in the natural environment is unknown. Here, we demonstrate that the substitution of membrane phospholipids for a variety of non-phosphorus lipids is a conserved response to P deficiency among phylogenetically diverse marine heterotrophic bacteria, including members of the Alphaproteobacteria and Flavobacteria. By deletion mutagenesis and complementation in the model marine bacterium Phaeobacter sp. MED193 and heterologous expression in recombinant Escherichia coli, we confirm the roles of a phospholipase C (PlcP) and a glycosyltransferase in lipid remodelling. Analyses of the Global Ocean Sampling and Tara Oceans metagenome data sets demonstrate that PlcP is particularly abundant in areas characterized by low phosphate concentrations. Furthermore, we show that lipid remodelling occurs seasonally and responds to changing nutrient conditions in natural microbial communities from the Mediterranean Sea. Together, our results point to the key role of lipid substitution as an adaptive strategy enabling heterotrophic bacteria to thrive in the vast P-depleted areas of the ocean.

• MeSH
• Alphaproteobacteria metabolismus   MeSH
• fosfáty chemie   MeSH
• fosfolipasy metabolismus   MeSH
• fosfolipidy chemie   MeSH
• fosfor chemie   MeSH
• fylogeneze MeSH
• fytoplankton metabolismus   MeSH
• glykosyltransferasy metabolismus   MeSH
• heterotrofní procesy MeSH
• mikrobiologie vody MeSH
• mořská voda mikrobiologie   MeSH
• oceány a moře MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• oceány a moře MeSH
• Středozemní moře MeSH

Euglenophyceae are unicellular algae with the majority of their diversity known from small freshwater reservoirs. Only two dozen species have been described to occur in marine habitats, but their abundance and diversity remain unexplored. Phylogenetic studies revealed marine prasinophyte green alga, Pyramimonas parkeae, as the closest extant relative of the euglenophytes' plastid, but similarly to euglenophytes, our knowledge about the diversity of Pyramimonadales is limited. Here we explored Euglenophyceae and Pyramimonadales phylogenetic diversity in marine environmental samples. We yielded 18S rDNA and plastid 16S rDNA sequences deposited in public repositories and reconstructed Euglenophyceae reference trees. We searched high-throughput environmental sequences from the TARA Oceans expedition and Ocean Sampling Day initiative for 18S rDNA and 16S rDNA, placed them in the phylogenetic context and estimated their relative abundances. To avoid polymerase chain reaction (PCR) bias, we also exploited metagenomic data from the TARA Oceans expedition for the presence of rRNA sequences from these groups. Finally, we targeted these protists in coastal samples by specific PCR amplification of two parts of the plastid genome uniquely shared between euglenids and Pyramimonadales. All approaches revealed previously undetected, but relatively low-abundant lineages of marine Euglenophyceae. Surprisingly, some of those lineages are branching within the freshwater or brackish genera.

• MeSH
• Chlorophyta klasifikace   genetika   MeSH
• DNA rostlinná genetika   MeSH
• Euglenida klasifikace   genetika   MeSH
• fotosyntéza MeSH
• fylogeneze MeSH
• genom chloroplastový * MeSH
• genom rostlinný MeSH
• polymerázová řetězová reakce MeSH
• ribozomální DNA genetika   MeSH
• RNA ribozomální 18S genetika   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Phytoplankton growth is limited in vast oceanic regions by the low bioavailability of iron. Iron fertilization often results in diatom blooms, yet the physiological underpinnings for how diatoms survive in chronically iron-limited waters and outcompete other phytoplankton when iron becomes available are unresolved. We show that some diatoms can use siderophore-bound iron, and exhibit a species-specific recognition for siderophore types. In Phaeodactylum tricornutum, hydroxamate siderophores are taken up without previous reduction by a high-affinity mechanism that involves binding to the cell surface followed by endocytosis-mediated uptake and delivery to the chloroplast. The affinity recorded is the highest ever described for an iron transport system in any eukaryotic cell. Collectively, our observations suggest that there are likely a variety of iron uptake mechanisms in diatoms besides the well-established reductive mechanism. We show that iron starvation-induced protein 1 (ISIP1) plays an important role in the uptake of siderophores, and through bioinformatics analyses we deduce that this protein is largely diatom-specific. We quantify expression of ISIP1 in the global ocean by querying the Tara Oceans atlas of eukaryotic genes and show a link between the abundance and distribution of diatom-associated ISIP1 with ocean provinces defined by chronic iron starvation.

• MeSH
• chloroplasty metabolismus   MeSH
• druhová specificita MeSH
• endocytóza * MeSH
• genový knockdown MeSH
• rozsivky fyziologie   MeSH
• siderofory metabolismus   MeSH
• transport proteinů MeSH
• vodní organismy metabolismus   MeSH
• železo metabolismus   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH