Seasonal Depth-Related Gradients in Virioplankton: Lytic Activity and Comparison with Protistan Grazing Potential in Lake Pavin (France)

International audienceThis study presents an original depth-related survey of virioplankton lytic activity in relation to prokaryotic production and potential protistan bacterivory in the deep (Zmax092 m) meromictic volcanic Lake Pavin (Massif Central, France). The sampling strategy was designed to be representative of the physico-chemical gradients of the water column of the lake, and of the seasonal variability as well, i.e. 12 different depths sampled in triplicates from April to December 2005. In the space, viral lytic activity estimated from the frequency of visibly infected prokaryotic cells and from burst size over the study period generally decreased with depth. This was viewed as a paradox compared to the abundances of viruses and prokaryotes and to the prokaryotic production which increased with depth. The seasonal variability in viral lytic activity was correlated with prokaryotic variables (abundance and production) in the deepest waters, i.e. from the hypolimnion downwards. Compared to previous studies known from the mixolimnion, we conclude that the deep waters in Lake Pavin represent an exclusive environment for heterotrophic prokaryotes whose seasonal activity offers an optimal and unique resource for thriving viral communities, some of which may be typical, endemic to the ambient dark, cold and stable deep water masses. Overall, the main findings in the present study get well around a previous statement that the ecology of the deepest waters of Lake Pavin is essentially driven by the dark viral loop (dissolved organic matter-prokaryotes- viruses) processes, which can sequester organic matters and nutrients for a long-lived turnover time. This is in agreement with recent demonstrations from marine systems that meso- and bathypelagic waters are optimal environments for viral survival and proliferation

BEEHOPE: um projeto de conservação das subespécies nativas de abelha da Europa Ocidental (linhagem M) à escala Europeia

O projeto BEEHOPE, com o título original “Honeybee conservation centres in western Europe - an innovative strategy using sustainable beekeeping to reduce honeybee decline”, foi um dos 10 aprovados na área da biodiversidade do 5º concurso transnacional (2013-2014) BiodivErsA/FACCE-JPI (http://www.biodiversa.org/766), subordinado ao tema “Promover sinergias e reduzir o compromisso entre o abastecimento de alimentos, biodiversidade e serviços dos ecossistemas”. A diversidade nativa das populações de abelha melífera (Apis mellifera) da linhagem da Europa ocidental (M) tem vindo a ser crescentemente ameaçada pela introdução massiva de colónias da linhagem da Europa oriental (C, onde se incluem as subespécies A. m. ligustica, A. m. carnica, A. m. macedónica etc.), e também por outros fatores bióticos (Varroa e vírus associados, Nosema etc.) e abióticos (pesticidas, perda e fragmentação de habitat, alterações climáticas etc.). É neste contexto que surge o projeto BEEHOPE, o qual tem por objetivo último contribuir para a conservação da diversidade genética das populações de abelha melífera da linhagem M.info:eu-repo/semantics/publishedVersio

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

The anterolateral ligament of the knee: unwrapping the enigma. Anatomical study and comparison to previous reports.

It has been suggested that the anterolateral ligament (ALL) of the knee may have importance in limiting rotational instability, and reconstruction may prevent a continued pivot-shift following anterior cruciate ligament surgery. However, the anatomy of this ligament has not been consistently reported in recent publications. We describe our experience of cadaveric dissection with reference to other published work.This article is freely available via Open Access. Click on the 'Additional Link' above to access the full-text from the publisher's site.Published (Open Access

Importance de la variabilité verticale dans un lac méromictique profond: diversité et activité lysogène des communautés virales

The main goal of this thesis was to assess qualitative, quantitative and functional significance of viruses in Lake Pavin, by taking into account the depth-related gradients in the water column. Specifically, we have examined the (i) spatio temporal dynamics of viral community diversity, (ii) significance of depth-related gradients in seasonal variations of viral abundance and lytic activity and (iii) relative significance of lysogenic 'life style'. From an original concentration protocol, we have shown that the dynamics of viral diversity in the lake was strongly linked to those of microbial communities. Similar for variations in viral seasonal abundance and lytic activity. Through the entire water column, microbial trophic network structure and the role of viruses in this network depended strongly on depth, with a simplification of trophic modes, of biological organization levels of communities, and of trophic interactions with depth. Biological limnology of the deep layers is reducte to viruses and prokaryotes, and is thus governed by the viral loop processes. Finally, up to 16 % of bacterioplankton could be lysogens. This way of life, antagonist with lytic one, depended on host availability and could be more a mechanism for the maintenance of viral traits, than can further have significant incidences on the evolutionary ecology of host communities. Overall, our results show that viruses are essential in the diversification and ecology of microbial communities, and in the matter and energy flows in the lake water column.Les objectifs de ce travail visaient à déterminer l'importance qualitative, quantitative et fonctionelle des virus dans le Lac Pavin, en tenant compte des gradients liés à la profondeur. Nous montrons que la dynamique de la diversité de l'abondance et de l'activité lytique du virioplancton du lac est étroitement associée à celle des communautés microbiennes. La prise en compte de l'ensemble de la colonne d'eau indique que la structure des réseaux trophiques microbiens et la place des virus dans ces réseaux dépendent de la profondeur. Finalement, jusqu'à 16% du bactérioplancton serait lysogène. Ce mode de vie, antagoniste à celui lytique, dépend de la disponibilité de l'hôte et serait un mécanisme de survie virale, pouvant avoir une incidence sur l'évolution adaptative des hôtes. Ces résultats montrent que les virus seraient essentiels dans la diversification et l'écologie des communautés microbiennes, et dans les flux de matière et d'énergie circulant dans la colonne d'eau

Importance de la variabilité verticale dans un lac méromictique profond (diversité et activité lysogène des communautés virales)

Les objectifs de ce travail visaient à déterminer l'importance qualitative, quantitative et fonctionelle des virus dans le Lac Pavin, en tenant compte des gradients liés à la profondeur. Nous montrons que la dynamique de la diversité de l'abondance et de l'activité lytique du virioplancton du lac est étroitement associée à celle des communautés microbiennes. La prise en compte de l'ensemble de la colonne d'eau indique que la structure des réseaux trophiques microbiens et la place des virus dans ces réseaux dépendent de la profondeur. Finalement, jusqu'à 16% du bactérioplancton serait lysogène. Ce mode de vie, antagoniste à celui lytique, dépend de la disponibilité de l'hôte et serait un mécanisme de survie virale, pouvant avoir une incidence sur l'évolution adaptative des hôtes. Ces résultats montrent que les virus seraient essentiels dans la diversification et l'écologie des communautés microbiennes, et dans les flux de matière et d'énergie circulant dans la colonne d'eauCLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Virus et prophages dans les écosystèmes aquatiques

International audienceIn this review, available data on the structure (diversity, abundance, biomass) and functional imprints (bacteriolysis, lysogeny, gene transfers, regulation of prokaryotic diversity) of natural viruses in the context of food webs in aquatic microbial ecology, and the related biogeochemical cycles, are summarized. Viruses are the most abundant, and probably the most diverse, biological entities in aquatic ecosystems and in the biosphere (i.e., viriosphere). Aquatic viruses typically exceed 107 particles/mL in mesotrophic conditions, the majority being represented by phages without tails and by tailed-phages such as members of the family Siphoviridae. Both types of phages have a small capsid and a small genome size, which is considered an evolutionary adaptation to planktonic life. Their contribution to microbial mortality is significant. There is strong evidence that phages exert a significant pressure on the community structure and diversity and on the diversification of potential hosts, mainly through two major pathways: biogeochemical catalysis from lysis products and horizontal gene transfers. In turn, phages are sensitive to environmental factors, both in terms of integrity and of infectivity. Some phages contain typical viral genes that code for biological functions of interest, such as photosynthesis. In general, development in viral ecology is a source of new knowledge for the scientific community in the domain of environmental sciences, but also in the context of evolutionary biology of living cellular organisms, the obligatory hosts for viruses. For example, the recent discovery of a giant virus that becomes ill through infection by another virus (i.e., a viriophage) is fuelling debate about whether viruses are alive. Finally, future research directions are identified in the context of general aquatic ecology, including ecological researches on cyanophages and other phytoplanktonic phages as a priority, primarily in freshwater lakes.Dans cette revue bibliographique, nous résumons les données acquises sur la structure (diversité, abondance, biomasse) et l’importance fonctionnelle (bactériolyse, lysogénie, transferts de gènes, régulation de la diversité des procaryotes) des virus d’origine naturelle, dans le contexte de la chaîne alimentaire en écologie microbienne aquatique et des cycles biogéochimiques associés. Les virus représentent la plus abondante et, sans doute, la plus diversifiée des entités biologiques présentes dans les écosystèmes aquatiques et dans la biosphère (c.-à-d., la viriosphère). On compte généralement plus de 107 particules virales par millilitre d’eau dans des conditions mésotrophes. La plupart de ces virus est représentée par des phages sans queue et par des phages à queue qui appartiennent principalement à la famille des Siphoviridae. Ces deux types de phages sont de petite taille du point de vue de leur capside et de leur génome, ce qui est considéré comme une adaptation à la vie planctonique. Leur contribution à la mortalité microbienne est significative. Il semble de plus en plus évident que les phages sont des agents exerçant une pression significative sur la structure et la diversité de la communauté et sur la diversification au sein des peuplements hôtes, principalement via deux voies : d’une part, la catalyse biogéochimique liée aux produits de la lyse virale et, d’autre part, les transferts horizontaux de gènes. En retour, les phages sont sensibles aux conditions environnementales, lesquelles conditionnent leur intégrité et leur pouvoir infectieux. Certains phages contiennent des gènes viraux typiques qui codent pour des fonctions biologiques d’intérêt, comme la photosynthèse. En général, l’écologie virale suscite un intérêt croissant dans le cadre des sciences de l’environnement, mais aussi de l’évolution adaptative de la vie cellulaire, support obligatoire de la prolifération virale. Ainsi, la découverte récente d’un viriophage, c’est-à-dire d’un virus infectieux d’un autre virus de plus grande taille, va faire avancer le débat sur la question à savoir si les virus sont des « êtres vivants ». Enfin, les futures orientations de la recherche dans le contexte général de l’écologie aquatique sont identifiées, notamment en ce qui concerne la priorité accordée à l’écologie des cyanophages et autres phages du phytoplancton, principalement dans les lacs dulçaquicoles

Differential localization and functional specialization of centrin analogs in the parasitic ciliate Trichodina pediculus

International audienc

Genotypic, size and morphological diversity of virioplankton in a deep oligomesotrophic freshwater lake (Lac Pavin, France)

International audienc

Fungal Parasitism: Life Cycle, Dynamics and Impact on Cyanobacterial Blooms

Many species of phytoplankton are susceptible to parasitism by fungi from the phylum Chytridiomycota (i.e. chytrids). However, few studies have reported the effects of fungal parasites on filamentous cyanobacterial blooms. To investigate the missing components of bloom ecosystems, we examined an entire field bloom of the cyanobacterium Anabaena macrospora for evidence of chytrid infection in a productive freshwater lake, using a high resolution sampling strategy. A. macrospora was infected by two species of the genus Rhizosiphon which have similar life cycles but differed in their infective regimes depending on the cellular niches offered by their host. R. crassum infected both vegetative cells and akinetes while R. akinetum infected only akinetes. A tentative reconstruction of the developmental stages suggested that the life cycle of R. crassum was completed in about 3 days. The infection affected 6 % of total cells (and 4 % of akinètes), spread over a maximum of 17 % of the filaments of cyanobacteria, in which 60 % of the cells could be parasitized. Furthermore, chytrids may reduce the length of filaments of Anabaena macrospora significantly by ‘‘mechanistic fragmentation’ ’ following infection. All these results suggest that chytrid parasitism is one of the driving factors involved in the decline of a cyanobacteria blooms, by direct mortality of parasitized cells and indirectly by the mechanistic fragmentation, which coul