Diversity and structure of sparids external microbiota (Teleostei) and its link with monogenean ectoparasites.

peer reviewed[en] BACKGROUND: Animal-associated microbial communities appear to be key factors in host physiology, ecology, evolution and its interactions with the surrounding environment. Teleost fish have received relatively little attention in the study of surface-associated microbiota. Besides the important role of microbiota in homeostasis and infection prevention, a few recent studies have shown that fish mucus microbiota may interact with and attract some specific parasitic species. However, our understanding of external microbial assemblages, in particular regarding the factors that determine their composition and potential interactions with parasites, is still limited. This is the objective of the present study that focuses on a well-known fish-parasite interaction, involving the Sparidae (Teleostei), and their specific monogenean ectoparasites of the Lamellodiscus genus. We characterized the skin and gill mucus bacterial communities using a 16S rRNA amplicon sequencing, tested how fish ecological traits and host evolutionary history are related to external microbiota, and assessed if some microbial taxa are related to some Lamellodiscus species. RESULTS: Our results revealed significant differences between skin and gill microbiota in terms of diversity and structure, and that sparids establish and maintain tissue and species-specific bacterial communities despite continuous exposure to water. No phylosymbiosis pattern was detected for either gill or skin microbiota, suggesting that other host-related and environmental factors are a better regulator of host-microbiota interactions. Diversity and structure of external microbiota were explained by host traits: host species, diet and body part. Numerous correlations between the abundance of given bacterial genera and the abundance of given Lamellodiscus species have been found in gill mucus, including species-specific associations. We also found that the external microbiota of the only unparasitized sparid species in this study, Boops boops, harbored significantly more Fusobacteria and three genera, Shewenella, Cetobacterium and Vibrio, compared to the other sparid species, suggesting their potential involvement in preventing monogenean infection. CONCLUSIONS: This study is the first to explore the diversity and structure of skin and gill microbiota from a wild fish family and present novel evidence on the links between gill microbiota and monogenean species in diversity and abundance, paving the way for further studies on understanding host-microbiota-parasite interactions

Host-microbiota-parasite interactions in two wild sparid fish species, Diplodus annularis and Oblada melanura (Teleostei, Sparidae) over a year: a pilot study

peer reviewed[en] BACKGROUND: The microbiota in fish external mucus is mainly known for having a role in homeostasis and protection against pathogens, but recent evidence suggests it is also involved in the host-specificity of some ectoparasites. In this study, we investigated the influence of seasonality and environmental factors on both fish external microbiota and monogenean gill ectoparasites abundance and diversity and assessed the level of covariations between monogenean and bacterial communities across seasons. To do so, we assessed skin and gill microbiota of two sparid species, Oblada melanura and Diplodus annularis, over a year and collected their specific monogenean ectoparasites belonging to the Lamellodiscus genus. RESULTS: Our results revealed that diversity and structure of skin and gill mucus microbiota were strongly affected by seasonality, mainly by the variations of temperature, with specific fish-associated bacterial taxa for each season. The diversity and abundance of parasites were also influenced by seasonality, with the abundance of some Lamellodiscus species significantly correlated to temperature. Numerous positive and negative correlations between the abundance of given bacterial genera and Lamellodiscus species were observed throughout the year, suggesting their differential interaction across seasons. CONCLUSIONS: The present study is one of the first to demonstrate the influence of seasonality and related abiotic factors on fish external microbiota over a year. We further identified potential interactions between gill microbiota and parasite occurrence in wild fish populations, improving current knowledge and understanding of the establishment of host-specificity

A New Isolate Beauveria bassiana GxABT-1: Efficacy against Myzus persicae and Promising Impact on the Beet Mild Yellow Virus-Aphid Association

peer reviewedWithin the context of ecofriendly alternatives to neonicotinoids, we explored the direct and endophytic potential of two Beauveria bassiana isolates, GHA from BotaniGard and the new endemic isolate GxABT-1, against the Sugar Beet Mild Yellow Virus (BMYV)-Myzus persicae pathosystem. A mortality rate of 96 and 91% was registered after 8 days of treatment with GHA and Gx-ABT-1, respectively. To assess the endophytic impact, sugar beet seeds were treated, and the ability of the fungi to colonize the plant was assessed and correlated with the aphids’ (1) life cycle, (2) attraction towards the plants, and (3) ability to transmit BMYV. Both fungi colonized the plants, and the GxABT-1 isolate impaired the aphids’ life cycle. Myzus persicae were more attracted to leaf discs from non-treated plants than to the fungal-treated ones. Interestingly, when the choice test dealt only with the fungal treatments, aphids were more attracted to leaves from plants harboring Gx-ABT-1 than those with GHA. Moreover, no significant impact was observed for BMYV transmission despite the slight decrease in the viral load in GxABT-1 isolate-treated plants. Our findings constitute a baseline to delve more into the performance of the new endemic isolate B. bassiana in other pathosystems using different treatment methods

Host Species and Body Site Explain the Variation in the Microbiota Associated to Wild Sympatric Mediterranean Teleost Fishes

peer reviewedMicroorganisms are an important component in shaping the evolution of hosts and as such, the study of bacterial communities with molecular techniques is shedding light on the complexity of symbioses between bacteria and vertebrates. Teleost fish are a heterogeneous group that live in a wide variety of habitats, and thus a good model group to investigate symbiotic interactions and their influence on host biology and ecology. Here we describe the microbiota of thirteen teleostean species sharing the same environment in the Mediterranean Sea and compare bacterial communities among different species and body sites (external mucus, skin, gills, and intestine). Our results show that Proteobacteria is the dominant phylum present in fish and water. However, the prevalence of other bacterial taxa differs between fish and the surrounding water. Significant differences in bacterial diversity are observed among fish species and body sites, with higher diversity found in the external mucus. No effect of sampling time nor species individual was found. The identification of indicator bacterial taxa further supports that each body site harbors its own characteristic bacterial community. These results improve current knowledge and understanding of symbiotic relationships among bacteria and their fish hosts in the wild since the majority of previous studies focused on captive individuals

Spécificité, diversité et évolution des communautés ectosymbiotiques chez les sparidés (Teleostei)

Monogeneans are ectoparasites, commonly abundant on the skin and gills of teleosts, generally very specific for their host. Several studies have suggested that the monogenean host specificity is driven by chemical compounds on the host surface which seem to be produced, at least partially, by the microbial communities in the mucus. The objective of this thesis was to characterize the microbial communities of the external mucus of natural populations of teleosts and to investigate their link with their monogenean ectoparasites. During this thesis, we have first (i) characterized the structure of the microbial and eukaryotic ecto- and endosymbiotic communities of different Mediterranean teleost families. We then focused on a host-parasite association, formed by Sparidae and monogeneans of the genus Lamellodiscus. The objective was to (ii) determine whether the structure of bacterial ectocommunities of Sparidae is one of the determinants of the specificity of Lamellodiscus. To do so, we studied the influence of environmental and host-specific factors on the variability of microbial communities within the Sparidae family and during an annual study of two species, and related this variability to the diversity and abundance of the Lamellodiscus communities. Finally, we investigated the existence of specificity filters within the Lamellodiscus genus. The objective was (iii) to compare the diversity and species composition of Lamellodiscus species on the skin and gills of Sparidae in order to determine the existence of a sorting mechanism between larvae (present on the skin) and adults (gills) in the natural environment.Les monogènes sont des ectoparasites abondants sur la peau et les branchies des téléostéens, généralement très spécifiques de leur hôte. Plusieurs études suggèrent que la spécificité des monogènes est régie par des composés chimiques présents à la surface de l'hôte, qui semblent être produits en partie par les communautés microbiennes du mucus. L’objectif de cette thèse est de caractériser les communautés microbiennes du mucus externe des populations naturelles de téléostéens et d'étudier le lien avec leurs ectoparasites monogènes. Au cours de cette thèse, nous avons (i) caractérisé la structure des communautés ecto- et endosymbiotiques microbiennes et eucaryotes de plusieurs familles de téléostéens méditerranéens. Puis, nous nous sommes focalisés sur une association hôte-parasite, formée des Sparidae et des monogènes du genre Lamellodiscus. L'objectif était de (ii) déterminer si la structure des ectocommunautés bactériennes de Sparidae est un des déterminants de la spécificité des Lamellodiscus. Pour cela, nous avons étudié l’influence de facteurs environnementaux et propres à l’hôte sur la variabilité des communautés microbiennes à l’échelle de la famille des Sparidae et lors d’un suivi annuel de deux espèces, et relié cette variabilité à la diversité et à l’abondance des communautés de Lamellodiscus présentes. Enfin, nous avons étudié l’existence de filtres de spécificité au sein du genre Lamellodiscus. L’objectif était (iii) de comparer la diversité et composition de ces espèces de Lamellodiscus de la peau et des branchies des sparidés afin de déterminer l’existence d’un « tri » entre les larves (présentes sur la peau) et les adultes (branchies) en milieu naturel

Specificity, diversity and evolution of ectosymbiotic communities in sparids (Teleostei)

Les monogènes sont des ectoparasites abondants sur la peau et les branchies des téléostéens, généralement très spécifiques de leur hôte. Plusieurs études suggèrent que la spécificité des monogènes est régie par des composés chimiques présents à la surface de l'hôte, qui semblent être produits en partie par les communautés microbiennes du mucus. L’objectif de cette thèse est de caractériser les communautés microbiennes du mucus externe des populations naturelles de téléostéens et d'étudier le lien avec leurs ectoparasites monogènes. Au cours de cette thèse, nous avons (i) caractérisé la structure des communautés ecto- et endosymbiotiques microbiennes et eucaryotes de plusieurs familles de téléostéens méditerranéens. Puis, nous nous sommes focalisés sur une association hôte-parasite, formée des Sparidae et des monogènes du genre Lamellodiscus. L'objectif était de (ii) déterminer si la structure des ectocommunautés bactériennes de Sparidae est un des déterminants de la spécificité des Lamellodiscus. Pour cela, nous avons étudié l’influence de facteurs environnementaux et propres à l’hôte sur la variabilité des communautés microbiennes à l’échelle de la famille des Sparidae et lors d’un suivi annuel de deux espèces, et relié cette variabilité à la diversité et à l’abondance des communautés de Lamellodiscus présentes. Enfin, nous avons étudié l’existence de filtres de spécificité au sein du genre Lamellodiscus. L’objectif était (iii) de comparer la diversité et composition de ces espèces de Lamellodiscus de la peau et des branchies des sparidés afin de déterminer l’existence d’un « tri » entre les larves (présentes sur la peau) et les adultes (branchies) en milieu naturel.Monogeneans are ectoparasites, commonly abundant on the skin and gills of teleosts, generally very specific for their host. Several studies have suggested that the monogenean host specificity is driven by chemical compounds on the host surface which seem to be produced, at least partially, by the microbial communities in the mucus. The objective of this thesis was to characterize the microbial communities of the external mucus of natural populations of teleosts and to investigate their link with their monogenean ectoparasites. During this thesis, we have first (i) characterized the structure of the microbial and eukaryotic ecto- and endosymbiotic communities of different Mediterranean teleost families. We then focused on a host-parasite association, formed by Sparidae and monogeneans of the genus Lamellodiscus. The objective was to (ii) determine whether the structure of bacterial ectocommunities of Sparidae is one of the determinants of the specificity of Lamellodiscus. To do so, we studied the influence of environmental and host-specific factors on the variability of microbial communities within the Sparidae family and during an annual study of two species, and related this variability to the diversity and abundance of the Lamellodiscus communities. Finally, we investigated the existence of specificity filters within the Lamellodiscus genus. The objective was (iii) to compare the diversity and species composition of Lamellodiscus species on the skin and gills of Sparidae in order to determine the existence of a sorting mechanism between larvae (present on the skin) and adults (gills) in the natural environment

Looking for cophylogenetic patterns in a mutualistic symbiosis between Soritinae (Foraminifera, Miliolida) and the genus Symbiodinium (Dinophyta, Suessiales)

peer reviewedIn aquatic habitats, Symbiodinium endosymbionts has been recorded in many differents hosts: in invertebrates such as anemones, corals, mollusks or in some eukaryotic microorganisms like ciliates and foraminifera. Nine Symbiodinium clades are currently defined and display distinct biogeographic patterns. According to several molecular studies, only some Symbiodinium clades are found in association with the Soritinae, but this biological system is currently very poorly known, as are the determinants of host specificity (i.e. ecological and/or phylogenetic) in this symbiotic association. The main objective of this work is to estimate the level of cospeciation between Soritinae and their Symbiodinium. Phylogenies were built from the 18S rDNA for the Soritinae and the ITS2 region for Symbiodinium. There is a large number of Soritinae and Symbiodinium strains in databases, with uncertain taxonomic status, so we used species delimitation techniques to define potential species. Molecular dating methods using fossil calibration points were used to assess if emergence and diversification is concomitant in hosts and their symbionts. The cospeciation level was tested using two types of cophylogenetic analyzes on our datasets: the first assesses global congruence between the two phylogenies, and the second infers evolutionary scenarios. Hosts and symbionts phylogenies are globally congruent, but no clear cophylogenetic scenario could be produced. However, localized congruences were inferred within a complex cophylogenetic history

A Comparative Study of the Dynamics and Diversity of Bdellovibrio and Like Organisms in Lakes Annecy and Geneva

International audienceBdellovibrio and like organisms (BALOs) are obligate bacterial predators of other Gram-negative bacteria. Here, we used quantitative PCR (qPCR) and recently developed specific primers which target the 16S rRNA gene to explore the abundance and distribution of three families of BALO belonging to the Oligoflexia class (i.e., Bdellovibrionaceae, Peredibacteraceae and Bacteriovoracaceae) over one year in the epilimnion and hypolimnion of Lakes Annecy and Geneva. Peredibacteraceae was the dominant group at all sampling points except at the bottom of Lake Geneva, where Bdellovibrionaceae was found in higher number. In addition, the abundance of BALOs increased significantly during the warmer months. Using high-throughput sequencing (Illumina Miseq), hundreds of OTUs were identified for Bdellovibrionaceae and Peredibacteraceae. Phylogenetic analysis suggests that Bdellovibrionaceae are more diverse than Peredibacteraceae and that some OTUs belong to new species of Bdellovibrionaceae. We also found that dominant OTUs were present simultaneously in the two lakes, while some others were specific to each lake, suggesting an adaptive pattern. Finally, both abundance and diversity of BALOs were poorly associated with abiotic factors except temperature, suggesting the importance of studying biotic relationships, assumed to play a greater role than physico-chemical variables in BALOs’ dynamics and distribution

Molecular approaches as an innovative tool to investigate monogenean host-specificity, using the Sparidae-Lamellodiscus host-parasite system

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