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

Editorial: Roles and mechanisms of parasitism in aquatic microbial communities

International audienc

Dysbiosis in inflammatory bowel disease: a role for bacteriophages?

International audienceIntestinal bacteria have been implicated in theinitiation and amplification of inflammatory bowel disease (IBD). The dysbiosis theory, reviewed by Tamboli et al (Gut 2004;53:1), is that an imbalance between putative ‘‘harmful'' versus ‘‘protective'' bacterial species may promote chronic intestinal inflammation

Correlation between some environmental variables and abundance of Almophrya mediovacuolata (Ciliophora: Anoplophryidae) endocommensal ciliate of an anecic earthworms (Oligochaeta: Annelida) in Bambui (North-West Cameroon)

This study was devoted to accessing the influence of some soil physico-chemical parameters on the abundance of Almophrya mediovacuolata Ngassam, 1983, astome ciliate of the digestive tract of earthworms (EW) of the species Alma nilotica collected along “Fa’a ntsa” stream in Bambui. The survey primarily involved soil samples collection from the same spots of EW collection and preparation for physico-chemical analysis; evaluation in situ of the volumic density (VD) of worms (number /dm3 soil), their dissection, isolation and counting of ciliates with respect to different portion of EW’s gut (fore, mid and hindgut). Furthermore, correlation analysis between soil physico-chemical parameters and biological responses (EW volumic density and ciliate abundance) were performed. The results reveal that EW abundance was positively and significantly correlated with the following physico-chemical parameters: Cation Exchange Capacity CEC (p <0.01) and Mg2+ (p <0.05). A positive and significant correlation was found between Almophrya mediovacuolata and the pH of KCl in the foregut and midgut (p <0.01) while a negative and significant correlation was found between the abundance of Almophrya mediovacuolata and Ca2+ in the foregut (p <0.05). Almophrya mediovacuolata were found mostly in the foregut. This result shows that each portion of the digestive tract of Alma nilotica can be considered as a set of natural microhabitat in which a number of physico-chemical factors generate ecological niches suitable for the survival of different species of microorganisms among which ciliated protozoa. The fore and midgut was noticed to be the preferential zones of Almophrya mediovacuolata.Keywords: Biotic parameters, ciliated protozoa, microhabitat, soil physico-chemical parameters

Virus, bactéries et protistes pathogènes du phytoplancton, le rôle insoupçonné des parasites dans le fonctionnement des écosystèmes aquatiques

International audienceMicroscopiques, les parasites sont la plupart du temps invisibles, mais présents partout. Ils infectent tous les organismes du monde vivant. La dernière décennie a révélé une incroyable diversité chez les parasites viraux, bactériens et eucaryotes. Ceux infectant le phytoplancton pourraient avoir une importance capitale dans la dynamique des populations algales et dans le fonctionnement des écosystèmes aquatiques, mais leur rôle est encore très largement méconnu à ce jour (Brussaard, 2004). Sur ces questions, la recherche ne fait que commencer

Distribution of Astomatia Schewiakoff, 1896 and Hysterocinetidae Diesing, 1866 (Ciliophora, Oligohymenophora) along the digestive tract of Alma emini (Oligochaete, Glossoscolecidae) is correlated with physico-chemical parameters

International audienceThe paper demonstrates the influence of physico-chemical parameters on the distribution of endocommensal ciliates through the gut of the earthworm Alma emini. We measured physico-chemical parameters of the intestinal liquid extracted with the vacuum aspiration technique and concomitantly recorded biological parameter (species abundance). Furthermore, correlation analysis between physico-chemical parameters and biological parameter was performed in different compartments. In the foregut, among the eleven species of Astomatia recorded, correlation was significant between Metaracoelophrya intermedia, Coelophrya roquei and Water Content (WC = 46.94 ± 7.77%). In the midgut, among the nine species of Hysterocinetidae recorded, a significant correlation was observed between Metaptychostomum ebebdae, Ptychostomum macrostomum and Electric Conductivity (EC = 84.55 ± 12.94 μS/ cm). In the same compartment, a significant correlation was also observed between Ptychostomum macrostomum and Total Dissolved Substance (TDS = 16.20 ± 3.46%). In the hindgut, eight species of Astomatia were found, among which significant correlation was obtained between Coelophrya roquei and Hydrogen potential (pH = 7.35 ± 0.16). In the same compartment, taking into account the eleven species of Hysterocinetidae recorded, a significant correlation was also obtained between Ptychostomum macrostomum and pH; Ptychostomum commune and WC (28.84 ± 3.97%). These results suggest that each part of the digestive tract of A. emini can be considered as a set of natural microhabitats in which certain physico-chemical factors generate ecological niches suitable for one or another group of species

Description of five new species of hysterocinetian ciliates (Ciliophora, Hysterocinetidae), endocommensal in a terrestrial oligochaete of the genus Alma from Cameroon

International audienceStudies on five new species of hysterocinetian ciliates, endocommensal within a terrestrial oligochaete from the genus Alma (Cameroon), reveal the existence of three distinct types of cytoskeletal topography within their adhesive apparatus. In the first topographical type, four superimposed antagonistic strata of skeletal fibres that correspond to the arrangement observed in the genus Ptychostomum, Stein 1860 are found. The second topographical type is characterized by the existence of an unorganized field of fibrillar structures forming a single dense mass in the central part of the sucker. For this, a new genus is created: Ptychostomoides, Nana, Fokam, Ntoungwa et al. n. g. The third type present in the genus Proptychostomoides, Nana, Fokam, Ntoungwa et al. n. g. differs from the latter by the existence of a bare patch within the central region of the adhesive apparatus. This new evidence of morphological diversification within the Hysterocinetidae supports a new approach to the systematics of this group

ASSESSMENT OF THE ADSORPTION OF AEROMONAS HYDROPHILA ON POLYTHENE IN SODIUM HYPOCHLORITE AND HYDROGEN PEROXIDE TREATED WATER

A study was carried out on Aeromonas hydrophila adhesion to polythene fragment at different cell growth phases in aquatic microcosm. The main purpose of this study was to assess adsorption capacity, adsorption intensity and kinetics of Aeromonas hydrophila on polythene in sodium hypochlorite (NaOCl) and hydrogen peroxide (H2O2) disinfected water. The mean abundance of adhered A. hydrophila sometimes reached 28 and 111CFU.cm-2 respectively in NaOCl and H2O2 treated water. The adsorption capacities of A. hydrophila cells fluctuated between 1 and 2.12x1057 and between 1 and 2.29x1027 adhered cells.cm-2 in NaOCl and H2O2 disinfected water respectively. The adsorption intensities of this bacterium ranged from -45.81 to 3.49x1019 and from 0.16 to 2.29x1027 respectively in NaOCl and H2O2 treated water. Adsorption capacity and adsorption intensity of A. hydrophila cells on polythene in NaOCl treated water were greater than that obtained in water disinfected with H2O2. Adhesion kinetics of A. hydrophila cells oscillated between 0.001 and 0.930 adhered cell.cm-2.h-1. Adsorption kinetics seem resulted from interactions between bacterial cells and substrates, and depended both on the fragment type and bacterial species. The values of A. hydrophila surface hydrophobicity fluctuated between 65.11 and 92.74% in NaOCl disinfected water and between 63.38 and 89.41% in H2O2 treated water. The mean values of contact angle ranged from 83.1±0.6 to 85.8±0.8°.   Adhesion of A. hydrophila on polythene is mediated amongst others by cell growth phases, cell surface hydrophobicity, cell kinetic adhesion, adsorption capacity and adsorption intensity

Novel haloarchaeal viruses from Lake Retba infecting Haloferax and Halorubrum species

The diversity of archaeal viruses is severely undersampled compared with that of viruses infecting bacteria and eukaryotes, limiting our understanding on their evolution and environmental impacts. Here, we describe the isolation and characterization of four new viruses infecting halophilic archaea from the saline Lake Retba, located close to Dakar on the coast of Senegal. Three of the viruses, HRPV10, HRPV11 and HRPV12, have enveloped pleomorphic virions and should belong to the family Pleolipoviridae, whereas the forth virus, HFTV1, has an icosahedral capsid and a long non-contractile tail, typical of bacterial and archaeal members of the order Caudovirales. Comparative genomic and phylogenomic analyses place HRPV10, HRPV11 and HRPV12 into the genus Betapleolipovirus, whereas HFTV1 appears to be most closely related to the unclassified Halorubrum virus HRTV-4. Differently from HRTV-4, HFTV1 encodes host-derived minichromosome maintenance helicase and PCNA homologues, which are likely to orchestrate its genome replication. HFTV1, the first archaeal virus isolated on a Haloferax strain, could also infect Halorubrum sp., albeit with an eightfold lower efficiency, whereas pleolipoviruses nearly exclusively infected autochthonous Halorubrum strains. Mapping of the metagenomic sequences from this environment to the genomes of isolated haloarchaeal viruses showed that these known viruses are underrepresented in the available viromes.Peer reviewe

Hygroregulation, a key ability for eusocial insects: Native Western European honeybees as a case study

Sociality has brought many advantages to various hymenoptera species, including their ability of regulating physical factors in their nest (e.g., temperature). Although less studied, humidity is known to be important for egg, larval and pupal development, and also for nectar concentration. Two subspecies of Apis mellifera of the M evolutionary lineage were used as models to test the ability of a superorganism (i.e. honeybee colony) to regulate the humidity in its nest (i.e. “hygroregulation hypothesis”) in four conservation centers: two in France (A. m. mellifera) and two in Portugal (A. m. iberiensis). We investigated the ability of both subspecies to regulate the humidity in hives daily, but also during the seasons for one complete year. Our data and statistical analysis demonstrated the capacity of the bees to regulate humidity in their hive, regardless of the day, season or subspecies. Furthermore, the study showed that humidity in beehives is stable even during winter, when brood is absent, and when temperature is known to be less stable in the beehives. These results suggest that humidity is important for honeybees at every life stage, maybe because of the ‘imprint’ of the evolutionary history of this hymenopteran lineage.This work was supported in part by the research project BEEHOPE funded by the European call for projects 2013-2014 BiodivERsA / FACCEJPI from research agencies of France (ANR-14- EBID-0001), Spain (PCIN-2014-090) and Portugal (BiodivERsA /0002/2014). I. Eouzan is financed by a doctoral grant from the Ministry of National Education, Higher Education and Research (France).info:eu-repo/semantics/publishedVersio