ALBERT

Description: Hydrocarbon seepage is a widespread process at the continental margins of the Gulf of Mexico. We used a multidisciplinary approach, including multibeam mapping and visual seafloor observations with different underwater vehicles to study the extent and character of complex hydrocarbon seepage in the Bay of Campeche, southern Gulf of Mexico. Our observations showed that seafloor asphalt deposits previously only known from the Chapopote Knoll also occur at numerous other knolls and ridges in water depths from 1230 to 3150 m. In particular the deeper sites (Chapopopte and Mictlan knolls) were characterized by asphalt deposits accompanied by extrusion of liquid oil in form of whips or sheets, and in some places (Tsanyao Yang, Mictlan, and Chapopote knolls) by gas emission and the presence of gas hydrates in addition. Molecular and stable carbon isotopic compositions of gaseous hydrocarbons suggest their primarily thermogenic origin. Relatively fresh asphalt structures were settled by chemosynthetic communities including bacterial mats and vestimentiferan tube worms, whereas older flows appeared largely inert and devoid of corals and anemones at the deep sites. The gas hydrates at Tsanyao Yang and Mictlan Knolls were covered by a 5-to-10 cm-thick reaction zone composed of authigenic carbonates, detritus, and microbial mats, and were densely colonized by 1–2 m-long tube worms, bivalves, snails, and shrimps. This study increased knowledge on the occurrences and dimensions of asphalt fields and associated gas hydrates at the Campeche Knolls. The extent of all discovered seepage structure areas indicates that emission of complex hydrocarbons is a widespread, thus important feature of the southern Gulf of Mexico.

Description: © The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Vigderovich, H., Liang, L., Herut, B., Wang, F., Wurgaft, E., Rubin-Blum, M., & Sivan, O. Evidence for microbial iron reduction in the methanic sediments of the oligotrophic southeastern Mediterranean continental shelf. Biogeosciences, 16(16), (2019): 3165-3181, doi: 10.5194/bg-16-3165-2019.

Description: Dissimilatory iron reduction is probably one of the oldest types of metabolisms that still participates in important biogeochemical cycles, such as those of carbon and sulfur. It is one of the more energetically favorable anaerobic microbial respiration processes and is usually coupled to the oxidation of organic matter. Traditionally this process is thought to be limited to the shallow part of the sedimentary column in most aquatic systems. However, iron reduction has also been observed in the methanic zone of many marine and freshwater sediments, well below its expected zone and occasionally accompanied by decreases in methane, suggesting a link between the iron and the methane cycles. Nevertheless, the mechanistic nature of this link (competition, redox or other) has yet to be established and has not been studied in oligotrophic shallow marine sediments. In this study we present combined geochemical and molecular evidences for microbial iron reduction in the methanic zone of the oligotrophic southeastern (SE) Mediterranean continental shelf. Geochemical porewater profiles indicate iron reduction in two zones, the uppermost part of the sediment, and the deeper zone, in the layer of high methane concentration. Results from a slurry incubation experiment indicate that the deep methanic iron reduction is microbially mediated. The sedimentary profiles of microbial abundance and quantitative PCR (qPCR) of the mcrA gene, together with Spearman correlation between the microbial data and Fe(II) concentrations in the porewater, suggest types of potential microorganisms that may be involved in the iron reduction via several potential pathways: H2 or organic matter oxidation, an active sulfur cycle, or iron-driven anaerobic oxidation of methane. We suggest that significant upward migration of methane in the sedimentary column and its oxidation by sulfate may fuel the microbial activity in the sulfate methane transition zone (SMTZ). The biomass created by this microbial activity can be used by the iron reducers below, in the methanic zone of the sediments of the SE Mediterranean.

Description: This study was supported by the joint grant of Israel Science Foundation and the National Natural Science Foundation of China (ISF-NSFC) (grant numbers 31661143022 (FW) and 2561/16 (OS)). Funding was provided to Hanni Vigderovich by the Mediterranean Sea Research Center of Israel.

Description: This study estimated the short-term decomposition effects of the invasive jellyfish Rhopilema nomadica on nutrient dynamics at the sediment-water interface in the Eastern Mediterranean Sea using core incubations. The degradation of R. nomadica has led to increased oxygen demand and acidification of overlying water as well as high rates of dissolved organic nitrogen and phosphate production.

Description: Sponges host a remarkable diversity of microbial symbionts, however, the benefit their microbes provide is rarely understood. Here, we describe two new sponge species from deep-sea asphalt seeps and show that they live in a nutritional symbiosis with methane-oxidizing (MOX) bacteria. Metagenomics and imaging analyses revealed unusually high amounts of MOX symbionts in hosts from a group previously assumed to have low microbial abundances. These symbionts belonged to the Marine Methylotrophic Group 2 clade. They are host-specific and likely vertically transmitted, based on their presence in sponge embryos and streamlined genomes, which lacked genes typical of related free-living MOX. Moreover, genes known to play a role in host–symbiont interactions, such as those that encode eukaryote-like proteins, were abundant and expressed. Methane assimilation by the symbionts was one of the most highly expressed metabolic pathways in the sponges. Molecular and stable carbon isotope patterns of lipids confirmed that methane-derived carbon was incorporated into the hosts. Our results revealed that two species of sponges, although distantly related, independently established highly specific, nutritional symbioses with two closely related methanotrophs. This convergence in symbiont acquisition underscores the strong selective advantage for these sponges in harboring MOX bacteria in the food-limited deep sea.

Description: We investigated seawater microbial abundance, activity and diversity in a site strongly influenced by submarine groundwater discharge (SGD). Three sampling campaigns (August 2020, February 2021 and July 2021) were conducted at a field site, highly influenced by SGD (Achziv, northern Israel), Each field campaign lasted 2-5 days and covered at least 2 tidal cycles. Pore-water samples were collected on the shoreline using piezometers (AMS piezometers that reach depths of 〈2 meters) and a portable peristaltic pump. The density (g cm-3), electric conductivity (mS/cm), temperature (°C) and pH, of surface seawater, porewater and groundwater were measured on-site at the time of the sampling. Samples for microbial analysis were collected from the piezometers and divided to aliquots: 1. For community analysis, samples were immediately filtered through polycarbonate 0.2 μm pore size filters, which were kept on ice and transported to the laboratory on the same day. Filter samples were stored frozen (-20°C) until DNA extraction (filtered pore-water were kept for dissolved nutrient measurements. After thawing, each filter was cut into small pieces using a sterile scalpel blade, which was placed immediately into PowerSoil DNA bead tubes and extracted with the dNeasy PowerSoil Kit (Qiagen, USA) following the standard protocol. 2. For Pico-/nano-phytoplankton and heterotrophic prokaryotic abundance, non-filtered samples were chilled on ice and transported to the laboratory on the same day. Samples (1.8 mL) were fixed with glutaraldehyde (final concentration 0.02 % v:v, Sigma-Aldrich 253 G7651), frozen in liquid nitrogen, and later stored at −80°C until analysis. The abundance of autotrophic pico- and nano-eukaryotes, Synechococcus and Prochlorococcus, and other heterotrophic prokaryotes (bacteria and archaea) was determined using an Attune® Acoustic Focusing Flow Cytometer (Applied Biosystems) equipped with a syringe based fluidic system and 488 and 405 nm lasers. To measure heterotrophic prokaryote abundance, a sample aliquot was stained with SYBR Green (Applied Biosystems). 3. Prokaryotic (bacteria and archaea) heterotrophic production was estimated using the 3H-leucine incorporation method. Photosynthetic carbon fixation rates were estimated using the 14C incorporation method.

Description: We investigated seawater microbial abundance, activity and diversity throughthree laboratory-controlled bottle incubations mimicking different mixing scenarios between SGD (either ambient or filtered through 0.1 µm/0.22 µm) and seawater to determine the contribution of SGD to the coastal microbial community. The experiments were conducted with five different treatments (including ambient seawater not exposed to SGD) in triplicates. The first experiment (Exp. 1) was designed to test the relative contribution of brackish discharged groundwater (salinity = 7.9 ppt vs. the ambient salinity of the SEMS of ~39.5 ppt) on the microbial productivity and abundance of reference coastal seawater by mixing different ratios (1, 5, 10 and 20% v:v) of discharged groundwater. Discharged groundwater was collected into acid-cleaned containers on the day the experiment was initiated near Achziv Nature Reserve (33° 3′52 N, 35° 6′14.94 E). The second and third experiments (Exp. 2; Exp.3) were designed to extend Exp. 1 and aimed to specifically investigate how groundwater-derived microorganisms affect the activity and abundance of marine organisms once discharged into the sea. For these experiments, fresh groundwater (FGW) was collected from drilling wells and pumped into 20 L acid-cleaned sample-rinsed carboys the same day the experiment was initiated. At the laboratory, fresh groundwater was either filtered through a 0.1 μm polycarbonate filter (Exp. 2) or serially filtered through 0.22 and 0.1 μm polycarbonate filter (Exp. 3) and the filtrate was added to seawater in different mixing scenarios. Ambient coastal seawater was collected by pumping at the Israel Oceanographic and Limnological Research Institute (IOLR) into acid-cleaned carboys, and mixed with either brackish groundwater (Exp.1) or fresh groundwater (Exp. 2, Exp. 3) at the desired ratios and filtration size. The duration of the experiments was 3-5 days, and samples were taken for the following analyses: chlorophyll a (Exp. 1 & 2, every 24Hr.), dissolved nutrient concentrations (Exp. 2 & 3 T zero and T final), flow cytometry (bacterial and phytoplankton abundance, every 24Hr.), primary and heterotrophic production rates (Exp. 1 & 2, every 24Hr.; Exp. 3 T zero and T final). Currently, little is known about the interactions between groundwater-borne and coastal seawater microbial populations, and groundwater microbes' role upon introduction to coastal seawater populations. Here, we investigated seawater microbial abundance, activity and diversity through laboratory-controlled bottle incubations mimicking different mixing scenarios between SGD (either ambient or filtered through 0.1 µm/0.22 µm) and seawater.

Description: We investigated seawater microbial abundance, activity and diversity in a site strongly influenced by submarine groundwater discharge (SGD). We combined in-situ observations and laboratory-controlled bottle incubations mimicking different mixing scenarios between SGD (either ambient or filtered through 0.1 µm/0.22 µm) and seawater. Three sampling campaigns (August 2020, February 2021 and July 2021) were conducted at a field site, highly influenced by SGD (Achziv, northern Israel), which we recently compared to a reference site (Shikmona) at the oligotrophic Israeli shallow rocky coast. Each field campaign lasted 2-5 days and covered at least 2 tidal cycles. Porewater samples were collected on the shoreline using piezometers (AMS piezometers that reach depths of 〈2 meters) and a portable peristaltic pump. The density (g cm-3), electric conductivity (mS/cm), temperature (°C) and pH, of surface seawater, porewater and groundwater were measured on-site at the time of the sampling. Samples for microbial analysis were collected from the piezometers and divided to aliquots: 1. For community analysis, samples were immediately filtered through polycarbonate 0.2 μm pore size filters, which were kept on ice and transported to the laboratory on the same day. Filter samples were stored frozen (-20°C) until DNA extraction (filtered porewater were kept for dissolved nutrient measurements. After thawing, each filter was cut into small pieces using a sterile scalpel blade, which was placed immediately into PowerSoil DNA bead tubes and extracted with the dNeasy PowerSoil Kit (Qiagen, USA) following the standard protocol. To generate 16S rRNA gene libraries, the V3–V4 hypervariable region of the 16S gene was amplified and sequenced on the Illumina MiSeq platform. Quality-filtered reads were imported into QIIME 2 platform, denoised, dereplicated, clustered and trimmed using the DADA2 plugin. Taxonomic assignment of the ASVs was achieved against the Silva database. The ASV table is provided under "additional metadata". Raw data from Illumina MiSeq sequencing are deposited to the National Center for Biotechnology Information (NCBI) Sequence Read Archive (SRA) under BioProject number PRJNA973031 (will be available upon publication). 2. For Pico-/nano-phytoplankton and heterotrophic prokaryotic abundance, non-filtered samples were chilled on ice and transported to the laboratory on the same day. Samples (1.8 mL) were fixed with glutaraldehyde (final concentration 0.02 % v:v, Sigma-Aldrich 253 G7651), frozen in liquid nitrogen, and later stored at −80°C until analysis. The abundance of autotrophic pico- and nano-eukaryotes, Synechococcus and Prochlorococcus, and other heterotrophic prokaryotes (bacteria and archaea) was determined using an Attune® Acoustic Focusing Flow Cytometer (Applied Biosystems) equipped with a syringe based fluidic system and 488 and 405 nm lasers. To measure heterotrophic prokaryote abundance, a sample aliquot was stained with SYBR Green (Applied Biosystems). 3. Prokaryotic (bacteria and archaea) heterotrophic production was estimated using the 3H-leucine incorporation method. Photosynthetic carbon fixation rates were estimated using the 14C incorporation method.