Geochemical Control of Methanogenesis in Cape Lookout Bight, North Carolina

Hydrogen exerts thermodynamic control over the exclusion of methanogens by sulfate reducers in Cape Lookout Bight, NC, marine sediments. This has been demonstrated by previous in situ measurements, but has never been demonstrated in a batch incubation of unamended sediments and has never been combined with identification of the microorganisms involved in this process. We made triplicate anoxic incubations of sediments from the upper 3 cm of sediment over 122 days while taking weekly samples for DNA extraction, cell counts, and measurements of methane, sulfate, and hydrogen. The headspaces of the bottles were initially gassed with nitrogen and the third was subsequently gassed with methane, although the methane disappeared within the first two weeks and after that the incubation served as a third replicate. While sulfate was present, the hydrogen concentration was maintained below 2 nM. Hydrogen started to rise as sulfate concentrations fell below 3 mM, coinciding with a small increase in methane. Only when sulfate has been depleted and the hydrogen concentrations rise was methane continuously produced. Quantitative PCR (qPCR) suggests that Methanosarcinales and Methanomicrobiales increase when sulfate is depleted in all three incubations. 16s rRNA gene Miseq tag libraries support the increase of these methanogens as well as a novel archaeal group, Kazan 3A-21, and sulfur-oxidizing bacteria. qPCR and tag libraries show that the methanogen-like archaea, ANME-1, increase during early methanogenesis, but the values are near detection limits and are therefore noisy. The tag libraries suggest that sulfate-reducing bacteria maintain similar population levels throughout the sulfate reduction phase, decrease as sulfate is depleted, and then rebound during the methanogenic phase. This most likely signifies a switch from sulfate reduction to syntrophic fermentation of organic matter with methanogens. Total cell counts demonstrate a decline in cells with the decrease of sulfate until a recovery corresponding with production of methane. Our results suggest that competition for hydrogen influences what metabolic processes can occur in marine sediments and that a diversity of sulfate reducers and methanogens are involved in this competition

Vector-soliton collision dynamics in nonlinear optical fibers

We consider the interactions of two identical, orthogonally polarized vector solitons in a nonlinear optical fiber with two polarization directions, described by a coupled pair of nonlinear Schroedinger equations. We study a low-dimensional model system of Hamiltonian ODE derived by Ueda and Kath and also studied by Tan and Yang. We derive a further simplified model which has similar dynamics but is more amenable to analysis. Sufficiently fast solitons move by each other without much interaction, but below a critical velocity the solitons may be captured. In certain bands of initial velocities the solitons are initially captured, but separate after passing each other twice, a phenomenon known as the two-bounce or two-pass resonance. We derive an analytic formula for the critical velocity. Using matched asymptotic expansions for separatrix crossing, we determine the location of these "resonance windows." Numerical simulations of the ODE models show they compare quite well with the asymptotic theory.Comment: 32 pages, submitted to Physical Review

Kinetics and Identities of Extracellular Peptidases in Subsurface Sediments of the White Oak River Estuary, North Carolina

Anoxic subsurface sediments contain communities of heterotrophic microorganisms that metabolize organic carbon at extraordinarily low rates. In order to assess the mechanisms by which subsurface microorganisms access detrital sedimentary organic matter, we measured kinetics of a range of extracellular peptidases in anoxic sediments of the White Oak River Estuary, NC. Nine distinct peptidase substrates were enzymatically hydrolyzed at all depths. Potential peptidase activities (Vmax) decreased with increasing sediment depth, although Vmax expressed on a per-cell basis was approximately the same at all depths. Half-saturation constants (Km) decreased with depth, indicating peptidases that functioned more efficiently at low substrate concentrations. Potential activities of extracellular peptidases acting on molecules that are enriched in degraded organic matter (d-phenylalanine and l-ornithine) increased relative to enzymes that act on l-phenylalanine, further suggesting microbial community adaptation to access degraded organic matter. Nineteen classes of predicted, exported peptidases were identified in genomic data from the same site, of which genes for class C25 (gingipain-like) peptidases represented more than 40% at each depth. Methionine aminopeptidases, zinc carboxypeptidases, and class S24-like peptidases, which are involved in single-stranded-DNA repair, were also abundant. These results suggest a subsurface heterotrophic microbial community that primarily accesses low-quality detrital organic matter via a diverse suite of well-adapted extracellular enzymes. IMPORTANCE Burial of organic carbon in marine and estuarine sediments represents a long-term sink for atmospheric carbon dioxide. Globally, ∼40% of organic carbon burial occurs in anoxic estuaries and deltaic systems. However, the ultimate controls on the amount of organic matter that is buried in sediments, versus oxidized into CO2, are poorly constrained. In this study, we used a combination of enzyme assays and metagenomic analysis to identify how subsurface microbial communities catalyze the first step of proteinaceous organic carbon degradation. Our results show that microbial communities in deeper sediments are adapted to access molecules characteristic of degraded organic matter, suggesting that those heterotrophs are adapted to life in the subsurface

Mariana Serpentinite Mud Volcanism Exhumes Subducted Seamount Materials: Implications for the Origin of Life.

The subduction of seamounts and ridge features at convergent plate boundaries plays an important role in the deformation of the overriding plate and influences geochemical cycling and associated biological processes. Active serpentinization of forearc mantle and serpentinite mud volcanism on the Mariana forearc (between the trench and active volcanic arc) provides windows on subduction processes.  Here, we present (1) the first observation of an extensive exposure of an undeformed Cretaceous seamount currently being subducted at the Mariana Trench inner slope; (2) vertical deformation of the forearc region related to subduction of Pacific Plate seamounts and thickened crust; (3) recovered Ocean Drilling Program and International Ocean Discovery Program cores of serpentinite mudflows that confirm exhumation of various Pacific Plate lithologies, including subducted reef limestone; (4) petrologic, geochemical and paleontological data from the cores that show that Pacific Plate seamount exhumation covers greater spatial and temporal extents; (5) the inference that microbial communities associated with serpentinite mud volcanism may also be exhumed from the subducted plate seafloor and/or seamounts; and (6) the implications for effects of these processes with regard to evolution of life. This article is part of a discussion meeting issue ‘Serpentine in the Earth system’

Mariana serpentinite mud volcanism exhumes subducted seamount materials: implications for the origin of life

The subduction of seamounts and ridge features at convergent plate boundaries plays an important role in the deformation of the overriding plate and influences geochemical cycling and associated biological processes. Active serpentinization of forearc mantle and serpentinite mud volcanism on the Mariana forearc (between the trench and active volcanic arc) provides windows on subduction processes. Here, we present (1) the first observation of an extensive exposure of an undeformed Cretaceous seamount currently being subducted at the Mariana Trench inner slope; (2) vertical deformation of the forearc region related to subduction of Pacific Plate seamounts and thickened crust; (3) recovered Ocean Drilling Program and International Ocean Discovery Program cores of serpentinite mudflows that confirm exhumation of various Pacific Plate lithologies, including subducted reef limestone; (4) petrologic, geochemical and paleontological data from the cores that show that Pacific Plate seamount exhumation covers greater spatial and temporal extents; (5) the inference that microbial communities associated with serpentinite mud volcanism may also be exhumed from the subducted plate seafloor and/or seamounts; and (6) the implications for effects of these processes with regard to evolution of life.Copyright 2020 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/ by/4.0/, which permits unrestricted use, provided the original author and source are credited

Beyond national narratives? : centenary histories, the First World War and the Armenian Genocide

In April 2015 the centenary of the Armenian Genocide was commemorated. Just like the First World War centenary, this anniversary has provoked a flurry of academic and public interest in what remains a highly contested history. This article assesses the state of the current historiography on the fate of the Ottoman Armenians. It focuses on the possibilities for moving beyond the national narratives which continue to dominate the field, in particular through connecting the case of the Armenian Genocide to what has been termed a ‘transnational turn’ in the writing of the history of the First World War

Cause of Death and Predictors of All-Cause Mortality in Anticoagulated Patients With Nonvalvular Atrial Fibrillation : Data From ROCKET AF

M. Kaste on työryhmän ROCKET AF Steering Comm jäsen.Background-Atrial fibrillation is associated with higher mortality. Identification of causes of death and contemporary risk factors for all-cause mortality may guide interventions. Methods and Results-In the Rivaroxaban Once Daily Oral Direct Factor Xa Inhibition Compared with Vitamin K Antagonism for Prevention of Stroke and Embolism Trial in Atrial Fibrillation (ROCKET AF) study, patients with nonvalvular atrial fibrillation were randomized to rivaroxaban or dose-adjusted warfarin. Cox proportional hazards regression with backward elimination identified factors at randomization that were independently associated with all-cause mortality in the 14 171 participants in the intention-to-treat population. The median age was 73 years, and the mean CHADS(2) score was 3.5. Over 1.9 years of median follow-up, 1214 (8.6%) patients died. Kaplan-Meier mortality rates were 4.2% at 1 year and 8.9% at 2 years. The majority of classified deaths (1081) were cardiovascular (72%), whereas only 6% were nonhemorrhagic stroke or systemic embolism. No significant difference in all-cause mortality was observed between the rivaroxaban and warfarin arms (P=0.15). Heart failure (hazard ratio 1.51, 95% CI 1.33-1.70, P= 75 years (hazard ratio 1.69, 95% CI 1.51-1.90, P Conclusions-In a large population of patients anticoagulated for nonvalvular atrial fibrillation, approximate to 7 in 10 deaths were cardiovascular, whereasPeer reviewe

Buried Alive: Analysis of Uncultured Microbes in Marine Sediments

The vast majority of microbes in marine sediments have yet to be isolated in pure culture, this leaves many questions as to their ecological relevance and relationship with other taxa and their environment. We applied next generation sequencing techniques to high resolution depth profiles of marine sediments and geochemical analyses to investigate microbial population abundance and composition with depth in Chapter 2. This revealed a putative methanotroph, ANME-1, to be the sole microbe capable of producing methane in the methane producing zone and the area suspected of methane oxidation. This suggests that these OTU’s of ANME-1 are capable of both methane production and oxidation, the mechanism used dependent upon geochemical conditions. In Chapter 3, RNA transcript abundance was combined with 16SrRNA gene composition analysis and long-term incubations of marine sediments to investigate microbial population succession in concert with the depletion of sulfate as a temporal analog for depth. This separated methane production from sulfate reduction, revealing an increase in abundance of ANME-3, a methanotroph, simultaneous to an increase in methane concentrations, indicating that this methanotroph is also capable of methane production. Additionally, methanotrophic archaea could not be stimulated to increase in abundance by the addition of methane to the sulfate reduction zone; again, ANME-3 only increased after sulfate was depleted and was observed alongside an increase in methane production, further supporting its role as a putative methane producer. Lastly, in Chapter 4 metabolomic profiles were combined with single cell amplified genomes to explore microbial life in serpentinization sourced mud volcanoes associated with the Mariana Forearc. These constitute the first single cell genomes isolated from marine sediments of this type and alkalinity. Overall, this work offers new insights into methanogenic metabolism flexibility, as well as an improved understanding of microbes associated with sediments influenced by serpentinization sourced fluids

Effect of steel reinforcement corrosion on the dynamic behavior of RC beams

International audienceCorrosion is one of the most common pathologies that affects reinforced concrete structures (RC). The fact that this phenomenon leads to a progressive loss of structural performance does not need further discussions. This loss of performance is a crucial issue for safety, especially when considering the coupling with an external loading such as an earthquake. The present study aims to quantify the time evolution of some quantities of interest, such as the eigenfrequencies, the modeshapes or the damping ratios, as functions of the corrosion degree. To reach this objective an extensive experi-mental campaign has been set up on simple but large-scale RC specimens. The consequences of the corrosion phenomenon on both the static and dynamic behaviors of beams are quantified, considering several steel configurations. In this paper, the experimental campaign is described. Especially, the accelerated corrosion method used is presented as well as the planned loading. The paper ends with a brief description of a simplified model which is under development. Due to its low computational demand, it will be able to be used within the framework of probability safety assessment (PSA) studie