Biology subjects

Cueff-Gauchard, V.

Publications and source records attributed to Cueff-Gauchard, V..

5 recordsLinked to original sources

bioRxiv2025

Evolutionary convergence and trophic diversity in hot vent and cold seep shrimps showcase a continuum of symbiosis

Convergent evolution offers a powerful lens through which to examine the selective forces shaping life in extreme environments. In deep-sea hot vents and cold seeps, invertebrates have independently evolved symbioses with chemosynthetic bacteria, but repeated origins of such associations within a family remain rare. Here, we investigate the evolutionary emergence of chemosymbiosis in the shrimp family Alvinocarididae across 22 species collected globally. Electron microscopy identified a gradient of epibiotic bacterial colonization within the cephalothoracic cavity, ranging from absent to dense filamentous mats, suggesting distinct trophic strategies. Isotope and lipid trophic markers confirmed difference in reliance on chemosynthetic production among sympatric species with different bacterial colonization from a single vent. Phylogenetic analysis reveals at least two independent origins of chemosymbiosis, suggesting evolutionary convergence. Microhabitat association data further show that symbiotic phenotypes are most common in shrimps occupying the hottest, most geofluid-enriched microhabitats, though exceptions suggest contributions from additional ecological or physiological constraints. Our findings reveal many alvinocaridids as gradually evolving towards symbiosis, highlighting the importance of intermediate cases to understand the pathways to chemosymbiosis. This study contributes to a broader understanding of the predictability of evolutionary outcomes in distinct habitats such as vents, with broader implications for resilience of deep-sea ecosystems.

evolutionary biology↗

bioRxiv2024

FISH, a new tool for in situ preservation of RNA in tissues of deep-sea mobile fauna.

Accessing the metabolic functioning of deep-sea animals in situ remains a technological challenge as the recovery time of samples is incompatible with the short lifespan of such molecules as mRNAs. Tools able to preserve RNA in situ exist but they are incompatible with the study of mobile fauna. Here we describe a new sampling tool, named FISH (Fixer In situ of Homogenized Substrates), implemented on a submersible and equipped with a number of new specific features to collect and preserve in situ tissue of mobile fauna. Connected to the suction pump of a submersible, FISH incorporates a sampling bowl to which two bottles of a preservative reagent are attached, a suction hose, and a support containing a motor connected to the sampling bowl by a magnetic coupling system. We used the deep-sea hydrothermal shrimp Rimicaris exoculata from the Mid-Atlantic Ridge as a model to test the suitability of our new tool. FISH was compared to two other sampling methods, which use a metatranscriptomic approach targeting microbial communities associated with cephalothorax symbionts. RNA quality, gene assignment and taxonomic and gene function diversity showed differences between in situ and on-board preservation of tissues. Of the alternative sampling methods tested, the suction sampler was clearly not suitable for RNA-based studies, while pressurized recovery showed results closer to the sample quality obtained with FISH sampling. The FISH sampler has therefore demonstrated to be a cost-effective and reliable tool to efficiently preserve RNA recovered from deep-sea environments.

molecular biology↗

bioRxiv2023

Symbioses of alvinocaridid shrimps from the South West Pacific: No chemosymbiotic diets but partially conserved gut microbiomes

Rimicaris exoculata shrimps from hydrothermal vent ecosystems are known to host dense epibiotic communities inside their enlarged heads and digestive systems. Conversely, other shrimps from the family, described as opportunistic feeders have received less attention. We examined the nutrition and bacterial communities colonizing "head" chambers and digestive systems of three other alvinocaridids - Rimicaris variabilis, Nautilocaris saintlaurentae and Manuscaris sp. - using a combination of electron microscopy, stable isotopes and sequencing approaches. Our observations inside "head" cavities and on mouthparts showed only a really low coverage of bacterial epibionts. In addition, no clear correlation between isotopic ratios and relative abundance of epibionts on mouthparts could be established among shrimp individuals. Altogether, these results suggest that none of these alvinocaridids rely on chemosynthetic epibionts as their main source of nutrition. Our analyses also revealed a substantial presence of several Firmicutes within the foreguts and midguts of these shrimps, which closest known lineages were systematically digestive epibionts associated with alvinocaridids, and more broadly from digestive systems of other crustaceans from marine and terrestrial ecosystems. Overall, our study opens new perspectives not only about chemosynthetic symbioses of vent shrimps, but more largely about digestive microbiomes with potential ancient and evolutionarily conserved bacterial partnerships among crustaceans.

evolutionary biology↗

bioRxiv2022

Anatomy and Symbiosis of the digestive system of the vent shrimps Rimicaris exoculata and Rimicaris chacei revealed through imaging approaches.

The shrimps Rimicaris exoculata and Rimicaris chacei are visually dominant fauna co-occurring at deep-sea hydrothermal sites of the Mid-Atlantic Ridge (MAR). Their co-existence was related to contrasted life-history traits, among which differences in their diet and reliance on chemoautotrophic symbionts at adult stage. Both shrimps are colonized by diversified chemosynthetic symbiotic microbial communities in their cephalothoracic cavity. Symbiotic association with bacteria was also evidenced in their digestive system, and the major lineages were identified through sequencing (Mycoplasmatales lineages mainly in the foregut and Deferribacteres lineages mainly in the midgut) but their clear distribution within each host species was not assessed. For the first time, we used Fluorescence in situ Hybridization (FISH) to visualize these lineages. Then, we described their association with digestive structures of both Rimicaris species. The aim was to identify possible differences between host species that could be related to their different life-history traits. For this purpose, we first developed specific FISH probes targeting Deferribacteres and Mycoplasmatales lineages identified in the digestive system of these shrimps. After signal specificity validation for each the new probe, we showed a partitioning of the bacterial lineages according to the digestive organ. Despite morphological differences between the foregut of R. exoculata and R. chacei that could be related to the adult diet, our FISH results showed overall similar distribution of digestive symbionts for the two host species. However, a more comprehensive study is needed with specimens at different life or molt stages to bring potentially host specific patterns out. Such comparative approach using FISH is now warranted thanks to our newly designed probes. These will be valuable tools to track symbiont lineages in the environment, allowing a better understanding of their relationship with their host along its life cycle, including acquisition mechanisms.

microbiology↗

bioRxiv2021

Role of Ori in Thermococcus barophilus

The mechanisms underpinning replication of genomic DNA in Archaea have recently been challenged. Species belonging to two different taxonomic orders grow well in the absence of an origin of replication, challenging the role of the replication origin in these organisms. Here, we pursue the investigation of the particular way some archaea manage their DNA replication with Thermococcus barophilus and the role of Ori in this Archaea. Surprisingly we discovered that T. barophilus uses its Ori all along the growth curve with marked increase at the end of exponential phase. Through gene deletion, we show that Ori utilization requires Cdc6, and that origin deletion results in increased time in lag phase and a moderate decrease of growth rate in mutants. The number of chromosomes are quite similar between both strains during exponential and early stationary phases but differs after 24h of growth where {Delta}TbOriC has only 6 chromosomes/cell compared to 10 for the reference strain (WT). Following 1hr of growth in fresh media, {Delta}TbOriC strains contains 3 chromosome copies/cell, whereas the WT contains only 1. We hypothesize that the T. barophilus might degrade DNA to obtain energy to start replication and cell division, whereas the {Delta}TbOriC must maintain more chromosomal copies in order to initiate DNA replication in the absence of an origin or replication. Finally, we analyzed the role of Ori at temperatures above or below the optimal temperature, revealing that Ori is important to start growth at those temperatures, suggesting that replication origins may be involved in stress response.

microbiology↗