Iron-rich microbial mats at low-temperature sites in deep-sea hydrothermal environments make a significant contribution to element cycling, especially the iron cycle. From these mats collected at the MIR zone (Trans-Atlantic Geotraverse hydrothermal field, Mid-Atlantic Ridge), enrichment cultures were performed to isolate strains involved in iron metabolism. Two strains, affiliated to Vibrio diazotrophicus (HER2-O and HER2-R), were isolated from this environment and might be able to oxidize iron under autotrophic and anaerobic or microaerophilic conditions, in addition to grow under organoheterotrophic conditions. In particular, genomic analyses revealed the presence of a c4 -type cytochrome (cyc1) that could be involved in electron transfer in the Fe(II)-oxidation pathway and a complete inorganic carbon fixation pathway (reductive glycine pathway), arguing in favor of growth based on autotrophic metabolism, using iron as an energy source. Prophages were identified in both genomes. Caudoviricetes-type virus morphotypes were evidenced by direct observations during growth under organoheterotrophic conditions. Genes providing metabolic adaptations to deep-sea hydrothermal vent conditions were also identified and could confer an ecological advantage to these two novel strains to thrive and compete effectively in metal-rich deep-sea environments. Their unexpected abilities regarding their potential to oxidize Fe(II), in addition to their physiological capacities, may help to explain their presence in iron-rich microbial mats.

In deep-sea hydrothermal vents, sulfur compounds are central for microbial bioenergetics. Despite its significant impact on the global sulfur cycle, anaerobic sulfur compound disproportionation remains the least understood metabolism, with only three bacterial strains having been investigated at the proteomic level for their sulfur disproportionation metabolism to date. Here, we present a comparative proteomics study of the chemolithoautotrophic sulfur-cycling species Dissulfuribacter thermophilus S69ᵀ. Upon thiosulfate disproportionation conditions, proteomics revealed a high abundance of a cytoplasmic thiosulfate reductase AB homologue (PhsAB-like) that might reductively cleave thiosulfate into sulfide and sulfite. Subsequent steps might involve enzymes from the dissimilatory sulfate reduction, with Apr and Sat potentially functioning in reverse to produce sulfate. Strain S69T exhibited enhanced growth under sulfite/dihydrogen, likely due to both sulfite respiration and disproportionation. Here, a range of new enzymes were more abundant. These included an enzyme containing NrfD, the MolyAB as well as two membranous tetrathionate reductase homologues. Other membranous oxidoreductases such as QmoABC, DsrMKJOP and Complex I, may contribute to the pathway, while autotrophic growth is likely sustained by the Wood-Ljungdahl pathway. These findings highlight the distinct enzymatic features of strain S69ᵀ compared to previously proteomically characterised sulfur-disproportionating strains, revealing novel enzymes that warrant further analysis.

In 2018, the island of Mayotte located in the western Indian ocean, has experienced a seismo-volcanic crisis linked to the birth of an impressive intraplate submarine volcano at the east of the island. This volcano, named Fani Maoré, which has not yet been the subject of microbiological studies, triggered the largest submarine eruptive event ever recorded. Close to the volcano’s summit is a singular meter-size structure containing abundant native sulfur mineralizations. While a wide variety of ecosystems, with more or less well documented microbial communities, are found in active volcanoes on the ocean floor, knowledge on microbial communities hosted in habitats such as sulfur-rich intraplate volcanoes, that are not located on hotspots, remains limited. Genome-resolved metagenomics, culture-based functional approaches, geochemical and mineralogical analyses were combined to characterize the geological and physico-chemical constraints of the environment surrounding the yellow deposit part of this hotspot volcano and the composition and functions of its microbial community. Geological and geochemical analyses indicated that this volcanic habitat had high concentrations in various sulfur species, including native sulfur, hydrogen sulfide and sulfate. Twenty-three Metagenome Assembled Genomes (MAGs) belonging to 8 different bacterial phyla, mainly Pseudomonadota, Bacteroidota and Campylobacterota, were reconstructed from the sulfur-rich deposit and analyzed. The vast majority of MAGs encoded genes for complete sulfur cycling metabolic pathways, in particular sulfur oxidation. Estimation of the cultivable microbial fraction revealed a diversity of microorganisms, with high growth rates for sulfur reduction, sulfate reduction with dihydrogen, and sulfur oxidation. Sulfur compound (S0, SO32− and S2O32−) disproportionation was also observed in cultures. The versatile genus Sulfurimonas was prevalent in culture at 6 and 20 °C, in the presence of different sulfur redox couples. Microbial communities, including taxa commonly found in ridge hydrothermal systems, were composed of autotrophic, heterotrophic or mixotrophic taxa using a large range of electron donors and acceptors to fuel their catabolism, particularly sulfur compounds in all common oxidation states. They had the genetic potential and physiological capacity to carry out all the metabolic reactions of the microbial sulfur cycle using the abiotic sulfur compounds present in their habitat. Representatives of the Sulfurimonas genus were among the main chemoautotrophs, since they predominated in eleven different temperature-redox pair culture combinations. Based on the observations, a conceptual model was proposed to describe the interactions in this sulfur-rich deposit that may occur between the microorganisms, the physico-chemical conditions and the sulfur compounds supplied by the environment.

Sea-floor massive sulfide deposits (SMS) harbor over 108 tons of mineral resources along the mid-ocean ridges representing a significant polymetallic reservoir [1]. These SMS deposits are mainly composed of iron and sulfur, but also contain copper, zinc, gold, silver and rare-earth elements, making them attractive for the mining industry. Little is known about the geo-biodiversity and ecosystem services associated with these SMS deposits especially the inactive or extinct ones. Deep dark chemosynthetic microbial ecosystems associated with these deep-sea habitats interact with the hydrothermal deposits during their aging process through biogeochemical metal and carbon cycles. Hence, characterization and quantification of carbon incorporation are required to estimate the carbon fluxes associated with active and inactive hydrothermal systems [2-4]. During the HERMINE 2 [5] and BICOSE 3 [6] oceanographic expeditions on Mid-Atlantic Ridge (MAR), we collected 36 mineralized samples on SMS deposits characterized by different relative ages and various degrees of oxidation. Carbon fixation autotrophic and heterotrophic rates were measured using radio-labelled substrates at in situ conditions (pressure and temperature) to evaluate distribution and environmental controls on energy and carbon fluxes. Phylogenetic and metabolic microbial diversity were also investigated by a metagenomics approach to define microbial functional pathways driving alteration and biogeochemical metal and carbon cycles in the hydrothermal deep biosphere. Here we show, for the first time at a slow spreading ridge (i.e MAR), that high rates of CO2 fixation support large microbial biomasses that inhabit “active” to “inactive” SMS. Given the large volumes of SMS habitats, these deposits could represent a significant CO2 sink in the deep-sea and should therefore be considered for environmental management.References:[1]. Hannington, M., Jamieson, J., Monecke, T., Petersen, S. & Beaulieu, S. The abundance of seafloor massive sulfide deposits. Geology 39, 1155–1158 (2011).[2]. Dover, V. & Lee, C. Inactive Sulfide Ecosystems in the Deep Sea: A Review. Front. Mar. Sci. 6, (2019).[3]. Cathalot, C. et al. Hydrothermal plumes as hotspots for deep-ocean heterotrophic microbial biomass production. Nat Commun 12, 6861 (2021).[4]. Achberger, A. M. et al. Inactive hydrothermal vent microbial communities are important contributors to deep ocean primary productivity. Nat Microbiol 9, 657–668 (2024).[5]. PELLETER Ewan & CATHALOT Cécile. HERMINE2 cruise,Pourquoi pas ? R/V. Preprint at https://doi.org/10.17600/18001851 (2022).[6]. CAMBON Marie-Anne. BICOSE 3 cruise,Pourquoi pas ? R/V. Preprint at https://doi.org/10.17600/18002399 (2023).

A coccoid-shaped, strictly anaerobic, hyperthermophilic and piezophilic organoheterotrophic archaeon, strain Iri35cT, was isolated from a hydrothermal chimney rock sample collected at a depth of 2300 m at the Mid-Atlantic Ridge (Rainbow vent field). Cells of strain Iri35cT grew at NaCl concentrations ranging from 1-5 % (w/v) (optimum 2.0 %), from pH 5.0 to 9.0 (optimum 7.0-7.5), at temperatures between 50 and 90 °C (optimum 75-80 °C) and at pressures from 0.1 to at least 50 MPa (optimum: 10-30 MPa). The novel isolate grew on complex organic substrates, such as yeast extract, tryptone, peptone or beef extract, preferentially in the presence of elemental sulphur or l-cystine; however, these molecules were not necessary for growth. Its genomic DNA G+C content was 54.63 mol%. The genome has been annotated and the metabolic predictions are in accordance with the metabolic characteristics of the strain and of Thermococcales in general. Phylogenetic analyses based on 16S rRNA gene sequences and concatenated ribosomal protein sequences showed that strain Iri35cT belongs to the genus Thermococcus, and is closer to the species T. celericrescens and T. siculi. Average nucleotide identity scores and in silico DNA-DNA hybridization values between the genome of strain Iri35cT and the genomes of the type species of the genus Thermococcus were below the species delineation threshold. Therefore, and considering the phenotypic data presented, strain Iri35cT is suggested to represent a novel species, for which the name Thermococcus camini sp. nov. is proposed, with the type strain Iri35cT (=UBOCC M-2026T=DSM 111003T).

A novel thermophilic, microaerophilic and anaerobic, hydrogen- sulphur- and thiosulphate-oxidising bacterium, designated MO1340(T), was isolated from a deep-sea hydrothermal chimney collected from the Lucky Strike hydrothermal vent field on the Mid-Atlantic Ridge. Cells were short, motile rods of 1.4-2.2 mu m length and 0.5-0.8 mu m width. Optimal growth was observed for a NaCl concentration of 2.5 % (w/v) at pH 6.5. As for other members of the genus Persephonella, strain MO1340(T) was strictly chemolithoautotrophic and could oxidise hydrogen, elemental sulphur or thiosulphate using oxygen as electron acceptor. Anaerobic nitrate reduction using hydrogen could also be performed. Each catabolic reaction had a different optimal growth temperature (65 to 75 degrees C) and an optimal dissolved oxygen concentration (11.4 to 119.7 mu M at 70 degrees C for aerobic reactions) that varied according to the electron donors utilised. These experimental results are consistent with the distribution of these catabolic substrates along the temperature gradient observed in active hydrothermal systems. They strongly suggest that this adaptive strategy could confer a selective advantage for strain MO1340(T) in the dynamic part of the ecosystem where hot, reduced hydrothermal fluid mixes with cold, oxygenated seawater. Phylogenetic analysis indicated that strain MO1340(T) was a member of the genus Persephonella within the order Hydrogenothermales as it shared a 16S rRNA gene sequence similarity <95.5 % and ANI respectively 75.66 % with closest described Persephonella (P. hydrogeniphila 29W(T)). On the basis of the physiological and genomic properties of the new isolate, the name Persephonella atlantica sp. nov. is proposed. The type strain is MO1340(T) (=UBOCC-M-3359(T) =JCM 34026(T)). (C) 2021 Elsevier GmbH. All rights reserved.

This study aims to compare the impact of oyster cultures on diagenetic processes and the phosphorus cycle in the sediments of the Aber Benoît and the Rivière d’Auray, estuary of Brittany, France. Our results showed clear evidence of the seasonal impact of oyster cultures on sediment characteristics (grain size and organic matter parameters) and the phosphorus cycle, especially in the Aber Benoît. At this site, seasonal variations in sulfide and Fe concentrations in pore waters, as well as Fe–P concentrations in the solid phase, highlighted a shift from a system governed by iron reduction (Reference) to a system governed by sulfate reduction (beneath oyster). This could be partly explained by the increase in labile organic matter (i.e., biodeposits) beneath oysters, whose mineralization by sulfate led to high sulfide concentrations in pore waters (up to 4,475 µmol l−1). In turn, sulfide caused an enhanced release of phosphate in the summer, as adsorption sites for phosphate decreased through the formation of iron–sulfide compounds (FeS and FeS2). In the Aber Benoît, dissolved Fe/PO4 ratios could be used as an indicator of phosphate release into oxic water. Low Fe/PO4 ratios in the summer indicated higher effluxes of phosphate toward the water column (up to 47 µmol m−2 h−1). At other periods, Fe/PO4 ratios higher than 2 mol/mol indicated very low phosphate fluxes. In contrast, in the Rivière d’Auray, the occurrence of macroalgae, stranding regularly all over the site, clearly masked the impact of oyster cultures on sediment properties and the phosphorus cycle and made the use of Fe/PO4 ratios more difficult in terms of indicators of phosphate release.

This study aims to investigate the role of spatial and temporal physical, biological and biogeochemical gradients on sediment biogeochemistry along a macrotidal and Si-rich estuary. Scanning and biogeochemical analyses were performed in the inner, mid and outer Aulne Estuary (France) at four seasons. The inner estuary shows high diagenetic activity linked to fluid mud dynamics and river loads. The highest authigenic phosphorus (Aut-P) concentrations ever found in the literature are observed in the inner estuary (18 μmol g −1 PS sediment). This is explained by a combination of favorable factors, i.e. the high organic matter and nutrient loads, the reductive conditions, the freshwater properties (low pH, OH − , sulfate and Mg 2+ concentrations), the increase of particle residence time by the upward convergence of particles due to residual currents, and allochthonous riverine Aut-P. We suggest that the high Si(OH) 4 concentrations (>400 μM) may even increase Aut-P precipitation through the increase of Fe–P formation in these low salinity conditions. In the mid estuary, erosion–deposition dynamics dominate in point bars and lead to the succession of poor and rich organic and authigenic phosphorus layers, recording thus the seasonality of matter loads and its seasonal translocation from the inner estuary. In the outer estuary, deposition rates are high and constant and biogeochemical properties are characteristic of marine environments. The precipitation of Aut-P from free phosphate (PO 4 3− ) is lower than in the inner estuary and might be limited by higher Mg 2+ concentrations in saline waters. This study highlights that small macrotidal estuaries, and especially their freshwater sediments, may constitute an important phosphorus sink through the precipitation of Aut-P. This precipitation could even be enhanced in fresh or brackish environments, thus increasing long term phosphorus storage and altering benthic fluxes of PO 4 3− to the pelagic ecosystem.

The high heterogeneity of silica cycling in coastal margins and the lack of silica data (compared to nitrogen and phosphorus) prevent the estimation of global silica retention in estuaries. In this study, the spatial and temporal variability of porewater silicic acid (Si(OH)(4)) profiles - that integrate benthic transport and reaction processes - was investigated at different spatial (metre, longitudinal and cross-section, intra-estuary) and temporal (tidal, seasonal) scales in two macrotidal estuaries, very close geographically but essentially differing in their shape. Studying the spatial and temporal variability of Si(OH)(4) concentrations in porewaters provided evidence for the importance of transport processes, e.g. bio-irrigation, tidal pumping, resuspension and any combination of these processes, in affecting Si(OH)(4) concentrations and fluxes and therefore temporary or permanent retention along the land ocean continuum. We confirm that aSiO(2) (amorphous silicate) transported by rivers and estuaries clearly needs to be better characterized as it provides an important source of reactive aSiO(2) to sediments. This study allows us to: (1) interrogate spatial and temporal scales, although both are most often in complete interaction; (2) design the most appropriate sampling schemes to be representative of any given system and to extrapolate at the scale of the whole estuary; (3) quantify uncertainty associated to the estimations of Si(OH)(4) stocks and fluxes in this type of ecosystem, essential for budget calculations. We showed that two adjacent small macrotidal estuaries, may exhibit different behaviours regarding Si retention. Temporary retention has been observed in the meanders of the Aulne Estuary and not along the more linear Elorn Estuary, demonstrating the importance of the morphology and hydrodynamic components of the estuarine filter. Research is needed in other systems and climatic zones, but our study suggests that the typology should not only account for the different types of land-ocean continuum (fjord, delta, mangrove...), but also incorporate the physical or biological attributes of the estuarine filter. (c) 2013 Elsevier Ltd. All rights reserved.

Bacterial community structure and some biogeochemical parameters were studied in the sediment of two Pacific oyster farming sites, Aber Benoît (AB) and Rivière d'Auray (RA) in Brittany (France), to examine the ecological impact of oysters and to evaluate the emission of sulfide and ammonia from sediment. At AB, the organic matter accumulated in the sediment beneath the oyster tables was rapidly mineralized, with strong fluxes of ammonia and sulfide that reached 1014 and 215 μmol m(-2) h(-1), respectively, in June 2007. At RA, the fluxes were about half as strong on average and better distributed through the year. The ammonia and sulfide concentrations in the overlying water never reached levels that would be toxic to oysters in either site, nor did hypoxia occur. Total culturable bacteria (TCB) varied greatly according to the temperature: from 1.6 × 10(4) to 9.4 × 10(7) cell g(-1) sediment. Inversely, the bacterial community structure remained surprising stable through the seasons, marginally influenced by the presence of oysters and by temperature. Bacterial communities appeared to be characteristic of the sites, with only one common phylotype, Vibrio aestuarianus, a potential oyster pathogen. These data refine the hypothesis of seawater toxicity to oysters because of ammonia and sulfide fluxes and show that the measured environmental factors had only a weak influence on bacterial community structure.

Vibrio aestuarianus is frequently found in coastal areas and can infect and induce mortalities in the pacific oyster Crassostrea gigas. However, nothing is known about its distribution and seasonality in the estuarine environment, especially where oyster farming is practiced. Its occurrence was investigated in sediment and oyster haemolymph at 2 oyster farms in Brittany (France) over 2 yr during 2 periods, from June to September 2007 and from February to June 2008. Total heterotrophic bacteria (HB) were cultured on marine agar while total Vibrio spp. and V aestuarianus were selectively numerated using thiosulfate citrate bile salts sucrose agar (TCBS agar) and the species-specific hybridisation method, respectively. PCR was performed to detect V aestuarianus in sediment when it became unculturable. Both total Vibrio spp. and V aestuarianus had a seasonal trend. The highest concentrations were recovered in the warmest months. Its abundance ranged from 10(2) to 4 x 10(5) CFU ml(-1) in haemolymph and from 10(3) to 1 x 10(4) CFU g(-1) in the sediment. Temperature was the main factor influencing the concentration of Vibrio spp. and V. aestuarianus in the sediment. Thus V aestuarianus might subsist during the cold seasons in the sediment, from which it can emerge when environmental conditions became favourable.

This is the 32. annual surveillance report concerning the nuclear power plant of Gravelines. Its very high power level results from six plant units located on the shore and is characterised by a cooling system with a coastal surface input and output. The production of electricity began in 1980 and reached maximum in 1986. Surveillance studies concern monitoring of fish populations (larvae and eggs of Sole and Sprat) or crustaceans (shrimps), benthic system (intertidal and sub-tidal) and pelagic system (hydrology, microbiology, phytoplankton, zooplankton). This survey deals with spatial and temporal approaches (i) study of the direct impact by comparison of the input and output seawater stations, (ii) study of medium and long term evolution of the area by comparison with a reference station. (authors)

The main objective of this work was to establish the influence of sex, maturity and reproduction on the contamination of the demersal fish Merluccius merluccius by organochlorine compounds. Polychlorinated biphenyls (PCBs) and p,p′DDE were quantified in muscle, liver and gonads of female and male hakes collected in the Gulf of Lions in 2004 and 2005. Observed levels appeared higher than the population of the Bay of Biscay and lower than the population of the Thyrrenian Sea. Contaminant fingerprints were roughly constant whatever the studied organ and the hake biological condition. Concentrations varied significantly according to the sex and maturity of hakes. Mature specimens were more contaminated than immature, and males presented higher levels than females. This sex effect can be linked to a lower growth rate of males, and a contaminant elimination during female spawning. Gonadal contamination depends on the importance of lipid content and increases with the maturation degree. Although the main organ of energy and PCB storage is the liver, muscle appears as the main contributor to the gonad contamination.

Carbon and nitrogen stable isotope ratios of particulate organic matter (POM) in surface water and 63–200μm-sized microphytoplankton collected at the fluorescence maximum were studied in four sites in the Gulf of Lions (NW Mediterranean), a marine area influenced by the Rhone River inputs, in May and November 2004. Some environmental (temperature, salinity) and biological (POM, Chlorophyll a and phaeopigments contents, phytoplankton biomass and composition) parameters were also analysed. Significantly different C and N isotopic signatures between surface water POM and microphytoplankton were recorded in all sites and seasons. Surface water POM presented systematically lower δ13C (∼4.2‰) and higher δ15N (∼2.8‰) values than those of microphytoplankton, due to a higher content of continental and detrital material. Seasonal variations were observed for all environmental and biological parameters, except salinity. Water temperature was lower in May than in November, the fluorescence maximum was located deeper and the Chlorophyll a content and the phytoplankton biomass were higher, along with low PON/Chl a ratio, corresponding to spring bloom conditions. At all sites and seasons, diatoms dominated the phytoplankton community in abundance, whereas dinoflagellate importance increased in autumn particularly in coastal sites. C and N isotopic signatures of phytoplankton did not vary with season. However, the δ15N of surface water POM was significantly higher in November than in May in all sites likely in relation to an increase in 15N/14N ratio of the Rhone River POM which influenced surface water in the Gulf of Lions. As it is important to determine true baseline values of primary producers for analysing marine food webs, this study demonstrated that C and N isotopic values of surface water POM cannot be used as phytoplankton proxy in coastal areas submitted to high river inputs.