Protist taxonomic and functional diversity in soil, freshwater and marine ecosystems

Protists dominate eukaryotic diversity and play key functional roles in all ecosystems, particularly by catalyzing carbon and nutrient cycling. To date, however, a comparative analysis of their taxonomic and functional diversity that compares the major ecosystems on Earth (soil, freshwater and marine systems) is missing. Here, we present a comparison of protist diversity based on standardized high throughput 18S rRNA gene sequencing of soil, freshwater and marine environmental DNA. Soil and freshwater protist communities were more similar to each other than to marine protist communities, with virtually no overlap of Operational Taxonomic Units (OTUs) between terrestrial and marine habitats. Soil protists showed higher γ diversity than aquatic samples. Differences in taxonomic composition of the communities led to changes in a functional diversity among ecosystems, as expressed in relative abundance of consumers, phototrophs and parasites. Phototrophs (eukaryotic algae) dominated freshwater systems (49% of the sequences) and consumers soil and marine ecosystems (59% and 48%, respectively). The individual functional groups were composed of ecosystem- specific taxonomic groups. Parasites were equally common in all ecosystems, yet, terrestrial systems hosted more OTUs assigned to parasites of macro-organisms while aquatic systems contained mostly microbial parasitoids. Together, we show biogeographic patterns of protist diversity across major ecosystems on Earth, preparing the way for more focused studies that will help understanding the multiple roles of protists in the biosphere

Test of active personal dosimeters for interventional radiology in realistic radiation fields

Abstract. In Interventional radiology, the medical staff stands close to the patient during his exposure to X-rays. Consequently, they can be exposed to relatively high doses due to radiation scattered by the patient and the medical equipment. Contrary to the passive dosemeters which assess the doses a posteriori, APDs are able to warn the medical staff when doses and/or dose rates exceed pre-defined radiation protection limits. At interventional radiology workplaces, APDs must be able to measure low-energy photons (10-120 keV) and pulsed radiations with relatively high instantaneous dose rates delivered by medical X-rays generators. Six ADP models, considered as suitable for application in interventional radiology on the basis of the results of a previous comparison jointly organised by EURADOS and IAEA, were selected to carry out a new comparison in 2007. This included radiation fields able to mimic the scattered and pulsed X-ray radiation fields met at workplace in hospitals. Irradiations took place at CEA-LIST LNHB (Saclay, France) and IRSN (Fontenay-aux-Roses, France). This paper describes the irradiation assemblies both for realistic and classic calibration facilities. The reference values of the personal dose equivalent, H p (10), were determined through measurements and simulations to calculate the response of the APDs. The results shed light on the ability of APDs to measure correctly the doses, when used in the specific low-energy spectra and dose rates of pulsed Xrays encountered in interventional radiology

Assessing the Diversity and Specificity of Two Freshwater Viral Communities through Metagenomics

Transitions between saline and fresh waters have been shown to be infrequent for microorganisms. Based on host-specific interactions, the presence of specific clades among hosts suggests the existence of freshwater-specific viral clades. Yet, little is known about the composition and diversity of the temperate freshwater viral communities, and even if freshwater lakes and marine waters harbor distinct clades for particular viral sub-families, this distinction remains to be demonstrated on a community scale

Lake sedimentary dna research on past terrestrial and aquatic biodiversity: Overview and recommendations

The use of lake sedimentary DNA to track the long-term changes in both terrestrial and aquatic biota is a rapidly advancing field in paleoecological research. Although largely applied nowadays, knowledge gaps remain in this field and there is therefore still research to be conducted to ensure the reliability of the sedimentary DNA signal. Building on the most recent literature and seven original case studies, we synthesize the state-of-the-art analytical procedures for effective sampling, extraction, amplification, quantification and/or generation of DNA inventories from sedimentary ancient DNA (sedaDNA) via high-throughput sequencing technologies. We provide recommendations based on current knowledge and best practises.</jats:p

Where less may be more: how the rare biosphere pulls ecosystems strings

Rare species are increasingly recognized as crucial, yet vulnerable components of Earth’s ecosystems. This is also true for microbial communities, which are typically composed of a high number of relatively rare species. Recent studies have demonstrated that rare species can have an over-proportional role in biogeochemical cycles and may be a hidden driver of microbiome function. In this review, we provide an ecological overview of the rare microbial biosphere, including causes of rarity and the impacts of rare species on ecosystem functioning. We discuss how rare species can have a preponderant role for local biodiversity and species turnover with rarity potentially bound to phylogenetically conserved features. Rare microbes may therefore be overlooked keystone species regulating the functioning of host-associated, terrestrial and aquatic environments. We conclude this review with recommendations to guide scientists interested in investigating this rapidly emerging research area

Caractérisation de l'activité protéolytique de différentes populations bactériennes du rumen

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Effects of phenolic acids on the proteolytic activity of the rumen bacteria Butyrivibrio fibrisolvens

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Interactions between proteolytic and cellulolytic rumen bacteria during hydrolysis of plant cell wall protein

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