Hypersaline Conditions Research Articles

Microbial responses to increased salinity in oiled upper tidal shorelines

The microbial degradation of crude oil stranded on seashores is usually much slower than that of dispersed oil at sea. This is usually attributed to nutrient limitation and higher oil concentrations on beaches than in dispersed plumes, in addition to the low moisture content and transient hypersaline conditions of the upper intertidal and supratidal zones. Here, we investigated the effect of hypersaline conditions, oil concentration, and nutrient limitation on the hydrocarbonoclastic activity. Beach sand, with oil concentrations of 1 and 10 mL/kg, was infiltrated with seawater at salinities of 30, 90, and 160 g/L to 20% saturation, with and without the addition of nutrients. Oil chemistry, 16 S rRNA gene amplicon, and metagenomic sequencing analyses were conducted every 30 days for 180 days. The biodegradation of aromatic hydrocarbons was much slower at higher salinities, while that of alkanes was not noticeably affected, and the addition of nutrients only marginally enhanced the biodegradation of hydrocarbons. The relative abundance and diversity of genera varied substantially with the increase in pore water salinity, whereby halophilic hydrocarbon-degrading microorganisms, particularly in the Marinobacter genus, were significantly abundant only under hypersaline conditions. The enzymes were considerably less abundant at high salinities, mainly for those associated to aromatic hydrocarbon degradation pathways. Consequently, occasional inundation of the upper parts of oiled sandy beaches with seawater to decrease the pore water salinity and reseed the contaminated region with indigenous hydrocarbon degraders, along with the concomitant addition of fertilizers, could be a suitable, non-destructive, and inexpensive response tool for enhancing the biodegradation of beached crude oil, particularly that of the aromatic fraction.

A risk assessment on Zostera chilensis, the last relict of marine angiosperms in the South-East Pacific Ocean, due to the development of the desalination industry in Chile

Seagrasses, which are considered among the most ecologically valuable and endangered coastal ecosystems, have a narrowly limited distribution in the south-east Pacific, where Zostera chilensis is the only remaining relict. Due to water scarcity, desalination industry has grown in the last decades in the central-north coasts of Chile, which may be relevant to address in terms of potential impacts on benthic communities due to their associated high-salinity brine discharges to subtidal ecosystems. In this work, we assessed ecophysiological and cellular responses to desalination-extrapolable hypersalinity conditions on Z. chilensis. Mesocosms experiments were performed for 10 days, where plants were exposed to 3 different salinity treatments: 34 psu (control), 37 psu and 40 psu. Photosynthetic performance, H2O2 accumulation, and ascorbate content (reduced and oxidized) were measured, as well as relative gene expression of enzymes related to osmotic regulation and oxidative stress; these, at 1, 3, 6 and 10 days. Z. chilensis showed a decrease in photosynthetic parameters such as electron transport rate (ETRmax) and saturation irradiance (EkETR) under hypersalinity treatments, while non-photochemical quenching (NPQmax) presented an initial increment and a subsequent decline at 40 psu. H2O2 levels increased with hypersalinity, while ascorbate and dehydroascorbate only increased under 37 psu, although decreased along the experimental period. Increased salinities also triggered the expression of genes related to ion transport and osmolyte syntheses, but salinity-dependent up-regulated genes were mostly those related to the reactive oxygen species metabolism. The relict seagrass Z. chilensis has shown to withstand increased salinities that may be extrapolable to desalination effects in the short-term. As the latter is not fully clear in the long-term, and considering the restricted distribution and ecological importance, direct brine discharges to Z. chilensis meadows may not be recommended.

Response to Hypersalinity of Four Halophytes Growing in Hydroponic Floating Systems: Prospects in the Phytomanagement of High Saline Wastewaters and Extreme Environments.

Hypersaline environments occur naturally worldwide in arid and semiarid regions or in artificial areas where the discharge of highly saline wastewaters, such as produced water (PW) from oil and gas industrial setups, has concentrated salt (NaCl). Halophytes can tolerate high NaCl concentrations by adopting ion extrusion and inclusion mechanisms at cell, tissue, and organ levels; however, there is still much that is not clear in the response of these plants to salinity and completely unknown issues in hypersaline conditions. Mechanisms of tolerance to saline and hypersaline conditions of four different halophytes (Suaeda fruticosa (L.) Forssk, Halocnemum strobilaceum (Pall.) M. Bieb., Juncus maritimus Lam. and Phragmites australis (Cav.) Trin. ex Steudel) were assessed by analysing growth, chlorophyll fluorescence and photosynthetic pigment parameters, nutrients, and sodium (Na) uptake and distribution in different organs. Plants were exposed to high saline (257 mM or 15 g L-1 NaCl) and extremely high or hypersaline (514, 856, and 1712 mM or 30, 50, and 100 g L-1 NaCl) salt concentrations in a hydroponic floating culture system for 28 days. The two dicotyledonous S. fruticosa and H. strobilaceum resulted in greater tolerance to hypersaline concentrations than the two monocotyledonous species J. maritimus and P. australis. Plant biomass and major cation (K, Ca, and Mg) distributions among above- and below-ground organs evidenced the osmoprotectant roles of K in the leaves of S. fruticosa, and of Ca and Mg in the leaves and stem of H. strobilaceum. In J. maritimus and P. australis the rhizome modulated the reduced uptake and translocation of nutrients and Na to shoot with increasing salinity levels. S. fruticosa and H. strobilaceum absorbed and accumulated elevated Na amounts in the aerial parts at all the NaCl doses tested, with high bioaccumulation (from 0.5 to 8.3) and translocation (1.7-16.2) factors. In the two monocotyledons, Na increased in the root and rhizome with the increasing concentration of external NaCl, dramatically reducing the growth in J. maritimus at both 50 and 100 g L-1 NaCl and compromising the survival of P. australis at 30 g L-1 NaCl and over after two weeks of treatment.

Sulfate reduction and homoacetogenesis at various hypersaline conditions: Implications for H2 underground gas storage

While interest in underground gas storage (UGS) of hydrogen (H2) in salt caverns is increasing in a growing H2 economy, knowledge of the microbial communities inhabiting those hypersaline environments is still scarce. High salt concentrations and limited availability of carbon (C) sources in cavern environments reduce microbial growth rates and metabolic activities. Growth conditions potentially change once H2 is stored in salt caverns. H2 is a universal electron donor that can facilitate autotrophic growth and subsequently growth of heterotrophs. In this study, a mixed culture enriched from hypersaline UGS sites was investigated in microcosm experiments with H2 atmosphere, testing the effect of different salt concentrations and C sources on methanogenesis, sulfate reduction and homoacetogenesis. Sulfate, acetate and lactate concentrations were quantified throughout a time span of 125 days of incubation and correlations with the microbial community structure and function were explored through 16S rRNA gene-based amplicon sequencing at the end of the experiment. Many of the amplicon sequence variants (ASVs) were only assigned to family or order level, reflecting that a large number of ASVs belong to previously undescribed taxa. At 4.4 M NaCl, close to cavern brine salinity, members of the Desulfovibrionales were absent when no C source other than CO2 was offered as the sole C source. This is in line with the finding that no sulfate reduction occurred at these conditions. Acetogenic Halanaerobiia dominated in these high salinity levels. Based on metagenome sequencing of four selected samples, we found that acetogenesis at autotrophic conditions relies on the activity of a halophilic homoacetogen, Acetohalobium sp. and that sulfate reduction can most likely be associated with a so far undescribed member of the Desulfonatronovibrionales. We further discuss the discrepancy between sulfate reduction at heterotrophic conditions, while no sulfate reduction was observed under autotrophic conditions although acetate was produced through the homoacetogenic activity of Acetohalobium. For the application of UGS of H2, this means that the presence and activity of the aforementioned microorganisms must be investigated, as they can eventually lead to the formation of acetate and allow sulfate reduction at relevant concentrations.

Life on the edge: Adaptations of Posidonia oceanica to hypersaline conditions in a Mediterranean lagoon system

Hypersaline stress is a major stressor in semi-enclosed coastal lagoons, affecting the distribution and survival of key foundation species. In this study, we investigated how Posidonia oceanica meadows responded physiologically and morphologically to different salinity concentrations both in-situ, across a natural saline gradient occurring inside the lagoon system, and in a mesocosm experiment. Leaf water relations, organic osmolytes, photosynthesis, respiration, Chlorophyll-a fluorescence, pigments content, and leaf growth were studied in P. oceanica from three different sites within the Stagnone of Marsala lagoon, as well as after exposing P. oceanica to a salinity level of 46 psu in a 30-day mesocosm experiment. Overall, we show that P. oceanica has evolved osmolar regulatory strategies and photosynthetic plasticity, allowing these meadows to cope with large salinity fluctuations (38 – 51.45 PSU). Our findings contribute to a better understanding of seagrass ecophysiological adaptation to extreme environmental conditions, as well as the importance of these populations serving as an experimental model at the Mediterranean scale for more comprehensive forecasting and management of environmental stress in these marine foundation species in an era of rapid environmental change.

Adaptive laboratory evolution to hypersaline conditions of lactic acid bacteria isolated from seaweed

Seaweed biomass has been proposed as a promising alternative carbon source for fermentation processes using microbial factories. However, the high salinity content of seaweed biomass is a limiting factor in large scale fermentation processes. To address this shortcoming, three bacterial species (Pediococcus pentosaceus, Lactobacillus plantarum, and Enterococcus faecium) were isolated from seaweed biomass and evolved to increasing concentrations of NaCl. Following the evolution period, P. pentosaceus reached a plateau at the initial NaCl concentration, whereas L. plantarum, and E. faecium showed a 1.29 and 1.75-fold increase in their salt tolerance, respectively. The impact that salt evolution had on lactic acid production using hypersaline seaweed hydrolysate was investigated. Salinity evolved L. plantarum produced 1.18-fold more lactic acid than the wild type, and salinity evolved E. faecium was able to produce lactic acid, while the wild type could not. No differences in lactic acid production were observed between the P. pentosaceus salinity evolved and wild type strains. Evolved lineages were analyzed for the molecular mechanisms underlying the observed phenotypes. Mutations were observed in genes affecting the ion balance in the cell, the composition of the cell membrane and proteins acting as regulators. This study demonstrates that bacterial isolates from saline niches are promising microbial factories for the fermentation of saline substrates, without the requirement of previous desalination steps, while preserving high final product yields.

Carbon metabolism and biogeography of candidate phylum "Candidatus Bipolaricaulota" in geothermal environments of Biga Peninsula, Turkey.

Terrestrial hydrothermal springs and aquifers are excellent sites to study microbial biogeography because of their high physicochemical heterogeneity across relatively limited geographic regions. In this study, we performed 16S rRNA gene sequencing and metagenomic analyses of the microbial diversity of 11 different geothermal aquifers and springs across the tectonically active Biga Peninsula (Turkey). Across geothermal settings ranging in temperature from 43 to 79°C, one of the most highly represented groups in both 16S rRNA gene and metagenomic datasets was affiliated with the uncultivated phylum "Candidatus Bipolaricaulota" (former "Ca. Acetothermia" and OP1 division). The highest relative abundance of "Ca. Bipolaricaulota" was observed in a 68°C geothermal brine sediment, where it dominated the microbial community, representing 91% of all detectable 16S rRNA genes. Correlation analysis of "Ca. Bipolaricaulota" operational taxonomic units (OTUs) with physicochemical parameters indicated that salinity was the strongest environmental factor measured associated with the distribution of this novel group in geothermal fluids. Correspondingly, analysis of 23 metagenome-assembled genomes (MAGs) revealed two distinct groups of "Ca. Bipolaricaulota" MAGs based on the differences in carbon metabolism: one group encoding the bacterial Wood-Ljungdahl pathway (WLP) for H2 dependent CO2 fixation is selected for at lower salinities, and a second heterotrophic clade that lacks the WLP that was selected for under hypersaline conditions in the geothermal brine sediment. In conclusion, our results highlight that the biogeography of "Ca. Bipolaricaulota" taxa is strongly correlated with salinity in hydrothermal ecosystems, which coincides with key differences in carbon acquisition strategies. The exceptionally high relative abundance of apparently heterotrophic representatives of this novel candidate Phylum in geothermal brine sediment observed here may help to guide future enrichment experiments to obtain representatives in pure culture.

Quaternary lacustrine carbonate deposits of the Great Basin, USA: Impact of climate, tectonics and substrate

ABSTRACTThe Great Basin included several lacustrine systems that accommodated extensive carbonate buildups: the Lahontan on the western side (dating back to 48 kyr cal bp), and the Bonneville (from 30 to 11.5 kyr cal bp) and Great Salt Lake (starting 11.5 kyr cal bp) on the eastern side of the basin. The eastern lakes show a transition from freshwater to hypersaline conditions. In contrast, the western lakes do not show any significant change from the originally prevailing freshwater conditions. Mapping of the carbonate buildups in the different lakes settings enables a comparison of a biotic versus an abiotic composition of the carbonate buildups, their morphologies and their specific spatial distributions. The morphology, size and distribution of the carbonate deposits are predominantly governed by seasonal to long‐term water level fluctuations, particular geomorphological heritage, fault‐induced processes, groundwater seepage and substrates. All of the lakes show a palaeoshoreline distribution with some buildups containing crusts, hemispheroid domes, and parts of complex domes resulting from climate‐induced lake level variations. However, the presence of columns and complex domes made up of mixed biotic/abiotic carbonates in the western Great Basin is related to the influx of groundwater. Winnemucca Lake and Pyramid Lake contain bigger buildups than the ones observed in the eastern Great Basin lakes. The presence of these large size buildups and thinolites in the Lahontan lacustrine system are a consequence of local hydrological processes associated with influenced groundwater flows through specific sedimentary structures (for example, from springs and delta fronts) and faults. This contrast in the distribution, composition and size of the buildups between the two sides of the Great Basin suggests local changes in water chemistry (for example, [Ca2+]) and groundwater influxes. This work provides a novel conceptual model for the formation of abiotic and/or biotic carbonate buildups in lacustrine settings.

Sedimentary and stratigraphic characteristics of the Maastrichtian Dukamaje formation of southern Iullemmeden Basin: Implications for the paleogeography of the Upper Cretaceous trans-Saharan seaway

The Maastrichtian Dukamaje Formation is a fossiliferous, shale- and marl-dominated unit, albeit with contentious paleodepositional environment, of the Rima Group, southern Iullemmeden Basin (northwestern Nigeria). The Basin holds records of the global sea-level highs of the Late Cretaceous - Paleocene. Hence, an improved understanding of the associated sedimentary infill will provide opportunity for an improved reconstruction of paleogeography and ancient stratigraphic sequences. Two different models (a low-energy, hypersaline lagoon and marsh based on predominance of fine grains with gypsum and preserved vertebrate fossils, or high energy/inshore, shallow marine environment supported with Libycoceras ammonite fossil) have been proposed by different workers who studied the same outcrop sections. The discrepancy in these previous models is partly due to inherent depositional complexities and the need to invoke deductive interpretations for epicontinental basins. Here, we used a systematic facies analysis (for the first time and with particular attention to stratigraphic relationships and correlation of some of the outcrop sections) integrated with previous biostratigraphic data in order to reconstruct the paleogeography of the Dukamaje Formation. The objectives are to describe the facies characteristics and provide a well-constrained interpretation for the depositional setting of the Dukamaje Formation. Results: two alternating, low-energy facies associations (marsh and lagoonal and restricted?/nearshore marine) were identified. The marsh and lagoonal facies association is characterised by fossiliferous and gypsiferous shale enriched in arenaceous foraminifera. The restricted marine facies association comprises highly fossiliferous nodular marls. The facies associations form a coastal sabkha facies succession, deposited in a marginal marine environment with likely brackish influence, under a warm tropical climate. The coastal sabkha facies succession is interpreted as a retrogradational system, which suggests that the Dukamaje Formation is a product of marine transgression of a low-lying, embayed, partially restricted, stable coast. By implication, the hypothesised Upper Cretaceous epicontinental sea (“trans-Saharan seaway”) across the North to West Africa was, rather than fully open, restricted in some places. Restrictions were related to presence of embayments in which hypersaline conditions developed due to low circulation. This model is largely consistent with the view of a partially restricted shallow marine for the Upper Cretaceous of the southern Iullemmeden Basin.

Molluscs along a salinity gradient in a hypersaline coastal lagoon, southern Gulf of Mexico

Abstract Molluscs are a diverse phylum in coastal lagoons because the numerous taxa collectively display broad ranges of optima and tolerance with respect to ambient conditions. We report on the taxonomic composition, habitat preferences and feeding guilds of molluscs from Río Lagartos coastal lagoon, Mexico. Molluscs were collected in the rainy season (September/October 2017), during the winter (Nortes) season (February 2018) and at the end of the warm, dry season (May 2018). Samples were taken using a Ponar dredge, a cylindrical PVC core barrel, or a beach seine. We studied the abiotic characteristics (sediment grain-size distributions, submersed aquatic vegetation abundance and salinity) to explore assemblage differences across the broad salinity gradient that characterizes the system (~30–78 PSU). Molluscs were represented by 39 species, 34 genera, 23 families and two classes. Stenohaline species were more numerous overall than euryhaline species, but their occurrence in samples was low (<20% of the samples). Stenohaline taxa lived primarily in environments characterized by marine salinity, and few were found under hypersaline conditions. We collected a smaller number of species than did studies carried out in the lagoon >35 years ago. Species accumulation curves revealed that the full species richness was not captured in our study. Euhaline environments displayed greater mollusc species richness and had a larger proportion of amount (mass) of submersed aquatic vegetation. In the hypersaline environments, species richness may be favoured by the lower dominance of sands. Suspension feeders were the most diverse group in both the euhaline and hyperhaline environments.

Unusual similarity of DNA solvation dynamics in high-salinity crowding with divalent cations of varying concentrations.

Double-stranded DNA bears the highest linear negative charge density (2e- per base-pair) among all biopolymers, leading to strong interactions with cations and dipolar water, resulting in the formation of a dense 'condensation layer' around DNA. Interactions involving proteins and ligands binding to DNA are primarily governed by strong electrostatic forces. Increased salt concentrations impede such electrostatic interactions - a situation that prevails in oceanic species due to their cytoplasm being enriched with salts. Nevertheless, how these interactions' dynamics are affected in crowded hypersaline environments remains largely unexplored. Here, we employ steady-state and time-resolved fluorescence Stokes shifts (TRFSS) of a DNA-bound ligand (DAPI) to investigate the static and dynamic solvation properties of DNA in the presence of two divalent cations, magnesium (Mg2+), and calcium (Ca2+) at varying high to very-high concentrations of 0.15 M, 1 M and 2 M. We compare the results to those obtained in physiological concentrations (0.15 M) of monovalent Na+ ions. Combining data from fluorescence femtosecond optical gating (FOG) and time-correlated single photon counting (TCSPC) techniques, dynamic fluorescence Stokes shifts in DNA are analysed over a broad range of time-scales, from 100 fs to 10 ns. We find that while divalent cation crowding strongly influences the DNA stability and ligand binding affinity to DNA, the dynamics of DNA solvation remain remarkably similar across a broad range of five decades in time, even in a high-salinity crowded environment with divalent cations, as compared to the physiological concentration of the Na+ ion. Steady-state and time-resolved data of the DNA-groove-bound ligand are seemingly unaffected by ion-crowding in hypersaline solution, possibly due to ions being mostly displaced by the DNA-bound ligand. Furthermore, the dynamic coupling of cations with nearby water may possibly contribute to a net-neutral effect on the overall collective solvation dynamics in DNA, owing to the strong anti-correlation of their electrostatic interaction energy fluctuations. Such dynamic scenarios may persist within the cellular environment of marine life and other biological cells that experience hypersaline conditions.

Spatial distribution of seawater carbonate chemistry and hydrodynamic controls in a low-inflow estuary

Coastal and estuarine systems play an important role in the global carbon cycle and often have complex carbonate chemistry dynamics due to a multitude of biogeochemical and physical drivers. Compared to classic estuaries, mechanisms driving the distribution of carbonate parameters in low-inflow estuaries are understudied. The spatial distribution of carbonate chemistry and hydrodynamic parameters were characterized in Morro Bay, a short and seasonally hypersaline estuary on the Central California Coast, during the dry, low-inflow season to better understand in situ modifications. Sampling transects were completed in the main channel in June, August, and September of 2018, bracketing both a high and low tide on each date. Temperature, salinity, total alkalinity, and dissolved inorganic carbon all increased from the mouth to the back of the estuary, with larger values observed during the low tide. pH values decreased towards the back of the bay, and had little variation between high and low tide for June and August transects. Flushing times (estimated using a salt-budget model approach) also increased toward the back of the bay which led to hypersaline conditions. Salinity alone only explained 20–33% of observed changes in total alkalinity and 13–22% of observed changes in dissolved inorganic carbon throughout the bay. The remaining changes in total alkalinity and dissolved inorganic carbon were likely driven by biogeochemical modifications enhanced by extended flushing times, particularly in the back bay. Prior to this project, Morro Bay experienced a recent, rapid collapse of eelgrass, the major biogenic habitat. In the last four years eelgrass in Morro Bay appears to be on a recovery trajectory; therefore, this study provides a baseline whereby future studies can evaluate carbonate chemistry changes associated with potential eelgrass recovery and expansion. This study highlights the unique hydrodynamic exchange in seasonally low-inflow estuaries and its potentially large role in influencing local carbonate chemistry and ocean acidification.

Effects of Salinity and Temperature on the Flexibility and Function of a Polyextremophilic Enzyme.

The polyextremophilic β-galactosidase enzyme of the haloarchaeon Halorubrum lacusprofundi functions in extremely cold and hypersaline conditions. To better understand the basis of polyextremophilic activity, the enzyme was studied using steady-state kinetics and molecular dynamics at temperatures ranging from 10 °C to 50 °C and salt concentrations from 1 M to 4 M KCl. Kinetic analysis showed that while catalytic efficiency (kcat/Km) improves with increasing temperature and salinity, Km is reduced with decreasing temperatures and increasing salinity, consistent with improved substrate binding at low temperatures. In contrast, kcat was similar from 2-4 M KCl across the temperature range, with the calculated enthalpic and entropic components indicating a threshold of 2 M KCl to lower the activation barrier for catalysis. With molecular dynamics simulations, the increase in per-residue root-mean-square fluctuation (RMSF) was observed with higher temperature and salinity, with trends like those seen with the catalytic efficiency, consistent with the enzyme's function being related to its flexibility. Domain A had the smallest change in flexibility across the conditions tested, suggesting the adaptation to extreme conditions occurs via regions distant to the active site and surface accessible residues. Increased flexibility was most apparent in the distal active sites, indicating their importance in conferring salinity and temperature-dependent effects.

Tepees associated with mobility of evaporite sulfate: The case of the Irati Formation, Permian of Paraná Basin, Brazil

ABSTRACTTepee structures, associated with cracks and intraformational breccias, are found in the basal part of the Thin Rhythmites Bed of the Irati Formation. The rhythmite alternates dark gray mm-thick laminae, formed by dolomicrite with crenulated microlamination rich in organic clay, and intermediate gray laminae, formed by dolarenite with peloids. Some of the rhythmic pairs are separated from each other by thin horizons (< 0.5 mm) with a concentration of quartz pseudomorphs of gypsum and/or pores resulting from bioturbation or dissolution. The close association of the peloids with microrosettes of early authigenic sodium sulfate, a typical salt of nonmarine brines, is suggestive of its formation under cyanobacterial action, favored by hypersaline conditions in inland lakes. This is consistent with the closing of the connection between the Paraná Basin and the Panthalassic Ocean, as has been suggested for the final stages of Irati sedimentation. The tepees analyzed are related to diapiric features of massive light gray dolomicrite, which is distinguished under the microscope as being poorer in organic matter and for presenting coalesced peloids (clots) rich in sodium sulfate. The hydroplastic rheology, overpressure, and density gradient required for the upward injection of light gray dolomicrite are attributed to supersaturation in water and the presence of eodiagenetic low-density hydrated sulfates (e.g., mirabilite and thenardite). Thus, the processes that form the tepees studied here differ from those described in previous models of lacustrine and lagoon tepees, especially regarding the fundamental role of the expansion and mobility of the sulfated dolomite sediment, controlled by the lake's hydrology and by the elevation of groundwater, without necessarily involving subaerial exposure processes.

Application of Archaea in Deubiquitinase-Like Enzyme Discovery and Activity Assay.

Archaea can be used as microbial platforms to discover new types of deubiquitinase-like (DUB-like) enzymes and to produce ubiquitin/ubiquitin-like (Ub/Ubl) protein conjugates as substrates for DUB/DUB-like activity assays. Here we outline how to use archaea to synthesize, purify, and assay the activity of DUB-like enzymes with unusual properties, including catalytic activity in hypersaline conditions, organic solvents, and high temperatures. We also outline the application of archaea in forming Ub/Ubl isopeptide linkages that include the covalent attachments of diverse archaeal and eukaryotic Ub/Ubls to target proteins. Archaea form these Ub/Ubl-linked protein conjugates in vivo, and the resulting products are found to serve as useful DUB substrates for in vitro assays.

Microbial electrosynthesis of acetate from CO2 under hypersaline conditions

Microbial electrosynthesis (MES) enables the bioproduction of multicarbon compounds from CO2 using electricity as the driver. Although high salinity can improve the energetic performance of bioelectrochemical systems, acetogenic processes under elevated salinity are poorly known. Here MES under 35–60 g L−1 salinity was evaluated. Acetate production in two-chamber MES systems at 35 g L−1 salinity (seawater composition) gradually decreased within 60 days, both under −1.2 V cathode potential (vs. Ag/AgCl) and −1.56 A m−2 reductive current. Carbonate precipitation on cathodes (mostly CaCO3) likely declined the production through inhibiting CO2 supply, the direct electrode contact for acetogens and H2 production. Upon decreasing Ca2+ and Mg2+ levels in three-chamber reactors, acetate was stably produced over 137 days along with a low cathode apparent resistance at 1.9 ± 0.6 mΩ m2 and an average production rate at 3.80 ± 0.21 g m−2 d−1. Increasing the salinity step-wise from 35 to 60 g L−1 gave the most efficient acetate production at 40 g L−1 salinity with average rates of acetate production and CO2 consumption at 4.56 ± 3.09 and 7.02 ± 4.75 g m−2 d−1, respectively. The instantaneous coulombic efficiency for VFA averaged 55.1 ± 31.4%. Acetate production dropped at higher salinity likely due to the inhibited CO2 dissolution and acetogenic metabolism. Acetobacterium up to 78% was enriched on cathodes as the main acetogen at 35 g L−1. Under high-salinity selection, 96.5% Acetobacterium dominated on the cathode along with 34.0% Sphaerochaeta in catholyte. This research provides a first proof of concept that MES starting from CO2 reduction can be achieved at elevated salinity.

Multilayer Feedforward Artificial Neural Network Model to Forecast Florida Bay Salinity with Climate Change

Florida Bay is a large, subtropical estuary whose salinity varies from yearly and seasonal changes in rainfall and freshwater inflows. Water management changes during the 20th century led to a long-term reduction in inflows that increased mean salinity, and the frequency and severity of hypersalinity. Climate change may exacerbate salinity conditions in Florida Bay; however, future salinity conditions have not been adequately evaluated. Here, we employed a Multilayer Feedforward Artificial Neural Network model to develop baseline salinity models for nearshore and offshore sites. Then, we examined the impacts of climate change on salinity using forecasted changes in various input variables under two climate change scenarios, representative concentration pathways (RCP) 4.5 and 8.5. Salinity could rise by 30% and 70% under the RCP4.5 and RCP8.5 forecasts, respectively. Climate change affected nearshore salinity significantly more, which rapidly fluctuated between mesohaline (5 to 18 PSU) and metahaline (40 to 55 PSU) to hypersaline conditions (>55 PSU). Offshore salinities ranged between euhaline (30 to 40 PSU) to metahaline (40 to 55 PSU) conditions. Our study suggests that increased freshwater flow would help maintain suitable estuarine conditions in Florida Bay during climate change, while our novel modeling approach can guide further Everglades restoration efforts.

Orbital-scale cyclicity and organic matter production in a Permian shallow mixed carbonate-siliciclastic system: Paraná Basin, Brazil

Mixed deposition in shallow seas is highly sensitive to climate variations and sea-level changes, which are the primary controls of high-frequency cycles in the stratigraphic record. The widespread Lower Permian mixed carbonate-siliciclastic succession of the Paraná Basin is composed of rhythmic organic-rich shale interbedded with dolostone. The strata are organized into several orders of magnitude of superimposed asymmetrical and symmetrical facies stacking patterns that developed in a broad epeiric sea, which extended over 106 km2 of Permian Gondwanan land. Detailed sedimentological and stratal stacking analysis allow the hierarchical organization to be identified in large-scale, medium-scale, small-scale, and elementary stacking patterns. The high-frequency depositional cycles compose four 3rd-order sequences. They comprise gray to black shale, marls, and peloidal to micritic dolostone. Due to the shallow water setting, the minimal available accommodation is responsible for the reduced cycle thickness and the overall mixed succession. The rhythmic deposits host highly productive hydrocarbon source rocks. Two widespread, thicker intervals of bituminous shale that develop during 3rd-order sequence transgression events are highly organic-rich oil shale (27 wt%). In addition, thin black shale laminae, which are interbedded with dolostone in high-frequency stacking patterns, are also rich in organic carbon (2–8 wt%). The alternation of high carbonate content and organic matter production was controlled by wet‒dry seasons and was related to total solar radiation maxima and minima. The total solar radiation maxima are translated into elevated carbonate precipitation due to shallower and hypersaline conditions. Total solar radiation minima induce freshwater discharge in shallow and hypersaline environments during wet stages, resulting in water column stratification. The occurrence of kerogen types III and IV, a high gammacerane index, variable Pr/Ph ratios, and C35 homohopane indices indicate this condition. In addition, the input of nutrient-rich terrigenous sediments favor algal blooms, enhancing anoxia in the bottom water, which is responsible for the organic-rich shale facies, as indicated by kerogen types I and II, high hydrogen index values, high C27/C29 sterane ratios, and higher β-carotane values. Based on the hierarchical organization and previous U–Pb SHRIMP zircon ages of volcanic ash layers, it is possible to correlate the observed succession with the global sea-level curve. A time span of 8.0 Ma is assessed for the Irati Sea, with an average of 2.7 Ma for the large-scale cycles. Furthermore, the high-frequency patterns that are compatible with the precession and eccentricity of the short (±100 ka) and major (±400 ka) periodicities of the Earth's orbit are estimated to be 26.6 ka, 135.5 ka, and 400 ka. The high-frequency cycles of organic-rich shales and carbonate that are deposited over thousands of years under long-term sea-level changes and are correlated along the basin suggest climatic control driven by the Earth's orbital perturbation, which is possible in the Milankovitch frequency band.

The evolution of seafloor environmental conditions in the southern Red Sea continental shelf during the last 30 ka

The southern Red Sea is affected by intense interactions between monsoon and sea level changes in a semi-closed environment. Still, the impacts on the wide shelves remain poorly documented. We investigate the seafloor environmental conditions on the southern Red Sea shelf over the last 30 ka through sedimentological (visual inspection, granulometry, bulk density), geochemical (organic carbon, calcium carbonate and nitrogen content) and micropaleontological (benthic foraminifera) observations in a previously dated sediment core (FA09) from the Farasan Islands Archipelago. Glacial sediments exhibit high density and low carbonate contents, whereas post-glacial sediments reflect increased biogenic productivity. Seafloor oxygenation was limited in most of the glacial interval, along with hypersaline conditions. During the maximum sea level lowstand, an enhanced presence of eutrophic-indicator benthic assemblages likely reflects efficient organic matter preservation induced by weak water ventilation. Our proxies combined with a previous surface-water productivity reconstruction reveals a coupling between organic matter flux to the seafloor and surface productivity levels in the southern Red Sea shelf, particularly pronounced during periods of enhanced summer monsoon. This pattern is often accompanied by a decrease in seafloor oxygenation. In contrast, well oxygenated and more oligotrophic seafloor conditions are recorded around the time of Heinrich Stadial 2, when previous work indicates a reduction in summer monsoon intensity and surface productivity levels. A drastic decrease of benthic foraminifera along with increased organic carbon contents in late glacial and late Holocene reflect oxygen-depleted seafloor conditions that we attribute to expansion of an intensified southern Red Sea oxygen minimum zone (OMZ).

The archaeal class Halobacteria and astrobiology: Knowledge gaps and research opportunities.

Water bodies on Mars and the icy moons of the outer solar system are now recognized as likely being associated with high levels of salt. Therefore, the study of high salinity environments and their inhabitants has become increasingly relevant for Astrobiology. Members of the archaeal class Halobacteria are the most successful microbial group living in hypersaline conditions and are recognized as key model organisms for exposure experiments. Despite this, data for the class is uneven across taxa and widely dispersed across the literature, which has made it difficult to properly assess the potential for species of Halobacteria to survive under the polyextreme conditions found beyond Earth. Here we provide an overview of published data on astrobiology-linked exposure experiments performed with members of the Halobacteria, identifying clear knowledge gaps and research opportunities.