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1st Iberian Ecological Society Meeting (2019); XIV Congreso Nacional de la Asociación Española de Ecología Terrestre (AEET), Ecology: an integrative science in the Anthropocene, 4-7 February 2019, Barcelona, Spain, Dinoflagellates are a key component of protist communities in planktonic marine environments, and their diversity and distributionhas been thoroughly studied worldwide. However, some environments, like benthic ones, remain poorly studied, and most researchfocuses on epiphytic toxic species. In this study, we have characterized the community of sand-dwelling dinoflagellates from someMediterranean Sea locations, an area lacking of studies on those organisms, with monthly samplings of coastal sediments duringsix months. The study was performed combining classical morphological techniques and high-throughput sequencing (HTS). Themorphological identification of organisms present in the sediment samples, combined with their molecular characterization usingsingle-cell PCR technique, allowed a refined classification of HTS reads. The results obtained show that the three studied locationshave similar richness and community composition. The communities are dominated by a few taxa, even though each site is charac-terized by the presence of some particular species. Those dominant taxa show a temporal dynamics from spring to summer. Whilesome increase their relative abundances along time, others decrease it, resulting in the same temporal pattern in all three locations.The combination of both approaches allowed to detect a large number of unknown species, and it reflects the need of further tax-onomic studies to characterize the diversity these organisms in coastal Mediterranean locations

International audience

Nucleariid amoebae (Opisthokonta) are known since the nineteenth century but their diversity and evolutionary history remain poorly understood. To overcome this limitation, we have obtained genomic and transcriptomic data from three Nuclearia, two Pompholyxophrys and one Lithocolla species using traditional culturing and single-cell genome (SCG) and single-cell transcriptome amplification methods. The phylogeny of the complete 18S rRNA sequences of Pompholyxophrys and Lithocolla confirmed their suggested evolutionary relatedness to nucleariid amoebae, although with moderate support for internal splits. SCG amplification techniques also led to the identification of probable bacterial endosymbionts belonging to Chlamydiales and Rickettsiales in Pompholyxophrys. To improve the phylogenetic framework of nucleariids, we carried out phylogenomic analyses based on two datasets of, respectively, 264 conserved proteins and 74 single-copy protein domains. We obtained full support for the monophyly of the nucleariid amoebae, which comprise two major clades: (i) Parvularia–Fonticula and (ii) Nuclearia with the scaled genera Pompholyxophrys and Lithocolla. Based on these findings, the evolution of some traits of the earliest-diverging lineage of Holomycota can be inferred. Our results suggest that the last common ancestor of nucleariids was a freshwater, bacterivorous, non-flagellated filose and mucilaginous amoeba. From the ancestor, two groups evolved to reach smaller (Parvularia–Fonticula) and larger (Nuclearia and related scaled genera) cell sizes, leading to different ecological specialization. The Lithocolla + Pompholyxophrys clade developed exogenous or endogenous cell coverings from a Nuclearia-like ancestor.This article is part of the discussion meeting issue ‘Single-cell ecology’.

XIII Reunión Ibérica de Algas Tóxicas y Biotoxinas Marinas (REDIBAL 2018) - XIII Reunión Ibérica de Fitoplancton Tóxico - XIII Iberian Toxic Algae and Marine Biotoxins Meeting, VI Simposio Internacional de Ciencias del Mar - VI International Symposium of Marine Sciences (ISMS 2018), 20- 22 June 2018, Vigo.-- 1 page, High-t hroughput metabarcoding techniques have become widely applied to characterize microbial communities. Studies on the community composition of marine coastal sediments are still scarce, although they represent a large reservoir of marine protists and the community composition is distinct to that of the water column. In this study, we characterized it using Illumina MiSeq sequencing of the V4 region of 18S rDNA on samples obtained in three different locations from the Mediterranean Sea during six months. All samples were subjected to two different treatments (DNA extraction directly from sediments, or previously eluting the organisms from the sediment using the seawater-ice Uhlig method). Our results show that despite being the methodology most commonly used in these studies, the low amount of sediments used in direct DNA extraction from sediments results in a larger dispersion of samples and replicates, in contrast to eluted samples, which allow the use of much larger amounts of sediments. As expected, the community composition and relative abundance of major taxonomic groups varied among treatments, with ciliates and dinoflagellates being predominant in eluted samples (>60% of reads). However, most abundant representatives were shared among treatments, representing an 80% of the total number of reads. Thus, both methods allowed the characterization of the community of protists. While the larger amount of sediment used in eluted samples resulted in higher richness values and a better capture of less abundant organisms, direct DNA extraction from low amount of sediments resulted in a better characterization of all present taxonomic groups but a larger variability among samples

5th Joint Meeting of the Phycological Society of America (PSA) & International Society of Protistologists Annual Meeting (ISOP), 29 July - 2 August 2018, Vancouver, BC, Canada

Modern phototrophic microbial mats are complex communities often used as analogs of major Precambrian ecosystems. Characterizing biotic, notably metabolic, interactions among different microbial mat members is essential to gain insights into the ecology and biogeochemistry of these systems. We applied 16S/18S rRNA metabarcoding approaches to characterize the structure of archaea, bacteria and protist communities from microbial mats collected along strong physicochemical (oxygen, salinity, temperature, depth) gradients in a shallow pond at the salar de Llamara (Chile). All mats were highly diverse, including members of virtually all known high-rank eukaryotic and prokaryotic taxa but also many novel lineages. Bacterial candidate divisions accounted for almost 50% of sequences in deeper mats, while Archaea represented up to 40% of sequences in some mat layers. Molecular phylogenetic analyses revealed six novel deeply divergent archaeal groups, along abundant and diverse Pacearchaeota and Woesearchaeota. Multivariate statistical analyses showed that local environmental conditions strongly influenced community composition. Co-occurrence network structure was markedly different between surface mats located in the oxygenated zone and mats located in transition and anoxic water layers. We identified potential biotic interactions between various high- and low-rank taxa. Notably, a strong positive correlation was observed between Lokiarchaeota and the poorly known candidate bacterial division TA06.

Early Earth and ExoEarths: origin and evolution of life (2017. Varsovia), The Danakil depression at the Afar region in Ethiopia is one of the most unique and extreme environments on Earth. At the confluence of three tectonic plates in the East African rift (Triple Afar Junction), the Afar Depression is the only place on Earth where the transition from continental to oceanic crust (rift-to drift process) can be observed on land. Several types of extreme environments co-exist in this area, including highly acidic hydrothermal springs linked to the local volcanic activity at the Dallol dome, as well as desert evaporites and hypersaline lakes that resulted from the intense evaporation of an ancient enclosed sea. Although there have been more than 50 years since the area was first explored, information about its chemistry and geology is limited, and its biology remains completely unknown. In January 2016 and in January 2017, after several years of preparation, we organized two interdisciplinary expeditions to the Dallol area in order to explore the presence of life and mineral-microbe interactions under these geochemical extremes. To do so, and in combination with geochemical and mineralogical studies, we are applying molecular analyses based on 16S rRNA gene sequences, metagenomic and cultural approaches. Here, we will present preliminary results on the presence of life and microbial diversity identified in several sites of this multi-extreme environment., Centre National de la Recherche Scientifique, Université Paris-Sud, Francia, Laboratoire de microbiologie des environnements extrêmes, Centre National de la Recherche Scientifique, Université de Bretagne Occidentale, Francia, Departamento de Ecología, Universidad Autónoma de Madrid, España, Unidad de Baleares, Instituto Geológico y Minero de España, España, Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas, España, Instituto Andaluz de Ciencias de la Tierra, Universidad de Granada, España, Laboratoire de Minéralogie, Physique des Matériaux et Cosmochimie , Centre National de la Recherche Scientifique, Université Pierre et Marie Curie, Francia