Showing papers by "University of Groningen published in 2000"

Fundamental obstacle for electrical spin injection from a ferromagnetic metal into a diffusive semiconductor

Abstract: We have calculated the spin-polarization effects of a current in a two-dimensional electron gas which is contacted by two ferromagnetic metals. In the purely diffusive regime, the current may indeed be spin-polarized. However, for a typical device geometry the degree of spin-polarization of the current is limited to less than 0.1% only. The change in device resistance for parallel and antiparallel magnetization of the contacts is up to quadratically smaller, and will thus be difficult to detect.

Job demands, perceptions of effort-reward fairness and innovative work behaviour

Abstract: Building on person-environment fit theory and social exchange theory, the relationship between job demands and innovative work behaviour was assumed to be moderated by fairness perceptions of the ratio between effort spent and reward received at work. This interaction of job demands with perceptions of effort-reward fairness was tested among 170 non-management employees from a Dutch industrial organization in the food sector. Results demonstrated a positive relationship between job demands and innovative work behaviour when employees perceived effort-reward fairness rather than under-reward unfairness.

The watershed transform: definitions, algorithms and parallelization strategies

Abstract: The watershed transform is the method of choice for image segmentation in the field of mathematical morphology. We present a critical review of several definitions of the watershed transform and the associated sequential algorithms, and discuss various issues which often cause confusion in the literature. The need to distinguish between definition, algorithm specification and algorithm implementation is pointed out. Various examples are given which illustrate differences between watershed transforms based on different definitions and/or implementations. The second part of the paper surveys approaches for parallel implementation of sequential watershed algorithms.

Analysis of intestinal flora development in breast-fed and formula-fed infants by using molecular identification and detection methods.

Abstract: Background:An obvious difference between breast-fed and formula-fed newborn infants is the development of the intestinal flora, considered to be of importance for protection against harmful micro-organisms and for the maturation of the intestinal immune system. In this study, novel molecular

Superconductivity on the border of itinerant-electron ferromagnetism in UGe2

Abstract: The absence of simple examples of superconductivity adjoining itinerant-electron ferromagnetism in the phase diagram has for many years cast doubt on the validity of conventional models of magnetically mediated superconductivity. On closer examination, however, very few systems have been studied in the extreme conditions of purity, proximity to the ferromagnetic state and very low temperatures required to test the theory definitively. Here we report the observation of superconductivity on the border of ferromagnetism in a pure system, UGe2, which is known to be qualitatively similar to the classic d-electron ferromagnets. The superconductivity that we observe below 1 K, in a limited pressure range on the border of ferromagnetism, seems to arise from the same electrons that produce band magnetism. In this case, superconductivity is most naturally understood in terms of magnetic as opposed to lattice interactions, and by a spin-triplet rather than the spin-singlet pairing normally associated with nearly antiferromagnetic metals.

Preoperative staging of non-small-cell lung cancer with positron-emission tomography.

Abstract: Background Determining the stage of non–small-cell lung cancer often requires multiple preoperative tests and invasive procedures. Whole-body positron-emission tomography (PET) may simplify and improve the evaluation of patients with this tumor. Methods We prospectively compared the ability of a standard approach to staging (computed tomography [CT], ultrasonography, bone scanning, and, when indicated, needle biopsies) and one involving PET to detect metastases in mediastinal lymph nodes and at distant sites in 102 patients with resectable non–small-cell lung cancer. The presence of mediastinal metastatic disease was confirmed histopathologically. Distant metastases that were detected by PET were further evaluated by standard imaging tests and biopsies. Patients were followed postoperatively for six months by standard methods to detect occult metastases. Logistic-regression analysis was used to evaluate the ability of PET and CT to identify malignant mediastinal lymph nodes. Results The sensitivity and sp...

Preoperative Staging of Non–Small-Cell Lung Cancer with Positron-Emission Tomography

Abstract: Background Determining the stage of non–small-cell lung cancer often requires multiple preoperative tests and invasive procedures. Whole-body positron-emission tomography (PET) may simplify and improve the evaluation of patients with this tumor. Methods We prospectively compared the ability of a standard approach to staging (computed tomography [CT], ultrasonography, bone scanning, and, when indicated, needle biopsies) and one involving PET to detect metastases in mediastinal lymph nodes and at distant sites in 102 patients with resectable non–small-cell lung cancer. The presence of mediastinal metastatic disease was confirmed histopathologically. Distant metastases that were detected by PET were further evaluated by standard imaging tests and biopsies. Patients were followed postoperatively for six months by standard methods to detect occult metastases. Logistic-regression analysis was used to evaluate the ability of PET and CT to identify malignant mediastinal lymph nodes. Results The sensitivity and sp...

Renal function, neurohormonal activation, and survival in patients with chronic heart failure

Abstract: Background—Because renal function is affected by chronic heart failure (CHF) and it relates to both cardiovascular and hemodynamic properties, it should have additional prognostic value. We studied whether renal function is a predictor for mortality in advanced CHF, and we assessed its relative contribution compared with other established risk factors. In addition, we studied the relation between renal function and neurohormonal activation. Methods and Results—The study population consisted of 1906 patients with CHF who were enrolled in a recent survival trial (Second Prospective Randomized study of Ibopamine on Mortality and Efficacy). In a subgroup of 372 patients, plasma neurohormones were determined. The baseline glomerular filtration rate (GFRc) was calculated using the Cockroft Gault equation. GFRc was the most powerful predictor of mortality; it was followed by New York Heart Association functional class and the use of angiotensin-converting enzyme inhibitors. Patients in the lowest quartile of GFR...

Biting and Chewing in Overdentures, Full Dentures, and Natural Dentitions

Abstract: It has been suggested that the provision of dental implants can improve the oral function of subjects with severely resorbed mandibles, possibly restoring function to the level experienced by satisfied wearers of conventional complete dentures. Nevertheless, a quantitative comparison has never been made and can be drawn from the literature only with difficulty, since studies differ greatly in methodology. To make such a comparison, we measured bite force and chewing efficiency by using identical methods in subjects with overdentures, complete full dentures, and natural dentitions. Our results indicated that bite forces achieved with overdentures on dental implants were between those achieved with artificial and natural dentitions. Chewing efficiency was significantly greater than that of subjects with full dentures (low mandible), but was still lower than that of subjects with full dentures (high mandible) and overdentures on bare roots. Differences in the height of the mandible revealed significant differences in chewing efficiency between the two full-denture groups. Furthermore, subjects with a shortened dental arch exerted bite forces similar to those of subjects with a complete-natural dentition, but their chewing efficiency was limited due to the reduced occlusal area. For all groups combined, a significant correlation was found between maximum bite force and chewing efficiency. Nearly half of the variation in chewing efficiency was explained by bite force alone.

Analysis of the fecal microflora of human subjects consuming a probiotic product containing Lactobacillus rhamnosus DR20.

Abstract: The composition of the fecal microflora of 10 healthy subjects was monitored before (6-month control period), during (6-month test period), and after (3-month posttest period) the administration of a milk product containing Lactobacillus rhamnosus DR20 (daily dose, 1.6 x 10(9) lactobacilli). Monthly fecal samples were examined by a variety of methods, including bacteriological culture analysis, fluorescent in situ hybridization with group-specific DNA probes, denaturing gradient gel electrophoresis of the V2-V3 region of 16S rRNA genes amplified by PCR, gas-liquid chromatography, and bacterial enzyme activity analysis. The composition of the Lactobacillus population of each subject was analyzed by pulsed-field gel electrophoresis of bacterial DNA digests in order to differentiate between DR20 and other strains present in the samples. Representative isolates of lactobacilli were identified to the species level by sequencing the V2-V3 region of their 16S rRNA genes and comparing the sequences obtained (BLAST search) to sequences in the GenBank database. DR20 was detected in the feces of all of the subjects during the test period, but at different frequencies. The presence of DR20 among the numerically predominant strains was related to the presence or absence of a stable indigenous population of lactobacilli during the control period. Strain DR20 did not persist at levels of >10(2) cells per g in the feces of most of the subjects after consumption of the product ceased; the only exception was one subject in which this strain was detected for 2 months during the posttest period. We concluded that consumption of the DR20-containing milk product transiently altered the Lactobacillus and enterococcal contents of the feces of the majority of consumers without markedly affecting biochemical or other bacteriological factors.

Towards a standardized notation and terminology in multiway analysis

Abstract: This paper presents a standardized notation and terminology to be used for three- and multiway analyses, especially when these involve (variants of) the CANDECOMP/PARAFAC model and the Tucker model The notation also deals with basic aspects such as symbols for different kinds of products, and terminology for three- and higher-way data The choices for terminology and symbols to be used have to some extent been based on earlier (informal) conventions Simplicity and reduction of the possibility of confusion have also played a role in the choices made Copyright (C) 2000 John Wiley & Sons, Ltd

The prognostic value of anti-cyclic citrullinated peptide antibody in patients with recent-onset rheumatoid arthritis.

Abstract: Objective To study the predictive value of anti–cyclic citrullinated peptide antibody (anti-CCP) in patients with recent-onset rheumatoid arthritis (RA). Methods Outcome in terms of physical disability (Health Assessment Questionnaire) and radiologic damage (modified Sharp method) over 3-year and 6-year periods was determined in an inception cohort of 273 RA patients who had had disease symptoms for >1 year at study entry. Anti-CCP titers were determined at baseline and considered positive as recently described. Their prognostic value was studied by means of multiple regression analysis, in which anti-CCP positivity, sex, age at study entry, IgM rheumatoid factor (IgM-RF) status, Disease Activity Score (DAS), HLA–DR4 status, and (in a separate group of patients) shared epitope status were used as independent variables, and radiologic damage and functional disability as dependent variables. Results Patients with anti-CCP had developed significantly more severe radiologic damage after 6 years of followup. In multiple regression analysis, radiologic damage after 6 years followup was significantly predicted by IgM-RF status, radiologic score at entry, and anti-CCP status. Functional disability was significantly predicted by sex, age at entry, IgM-RF status, and DAS. Conclusion Our data show that in almost 70% of RA patients, anti-CCP antibody is present at the early stages of disease. Anti-CCP–positive patients developed significantly more severe radiologic damage than patients who were anti-CCP negative, although in multiple regression analysis the additional predictive value was rather moderate.

Phosphoramidites: marvellous ligands in catalytic asymmetric conjugate addition.

Abstract: The development of an efficient catalytic system for enantioselective carbon−carbon bond formation by 1,4-addition of organometallic reagents (organolithium, Grignard, and organozinc reagents) to enones is a major challenge in organic synthesis. This Account presents the breakthrough realized in this field using chiral phosphoramidite ligands for copper-catalyzed dialkylzinc additions. Applications in catalytic routes to cycloalkanones as well as tandem and annulation procedures with excellent enantioselectivities are discussed.

Formation of Supported Phospholipid Bilayers from Unilamellar Vesicles Investigated by Atomic Force Microscopy

Abstract: Since their introduction through the work of McConnell et al. in the early 80s, supported phospholipid bilayers (SPBs) have proven to be a versatile model system for investigating a wide variety of phenomena. Despite their continuous application in fundamental as well as applied research fields, the mechanism by which SPBs are formed from suspensions of unilamellar vesicles remains poorly understood. Utilizing the ability of atomic force microscopy (AFM) to investigate processes in situ and in real time, we have studied the early stages of SPB formation on mica. Unilamellar vesicles of various sizes, composed of zwitterionic phospholipids, were prepared by sonication or extrusion. Vesicles of all sizes investigated were found to adsorb to mica. Unruptured vesicles forming supported vesicular layers (SVLs), as well as disks, formed as a result of vesicle rupture, could be visualized by AFM. The behavior of the SVLs was found to depend on the vesicle size, the lipid concentration, and the presence or absenc...

The multicultural personality questionnaire: a multidimensional instrument of multicultural effectiveness

Abstract: In today's global business environment, executive work is becoming more international in orientation. Several skills and traits may underlie executive success in an inter national environment. The Multicultural Personality Questionnaire was developed as a multidimensional instrument aimed at measuring multicultural effectiveness. The questionnaire has scales for Cultural Empathy, Openmindedness, Emotional Stability, Orientation to Action, Adventurousness/Curiosity, Flexibility, and Extraversion. In a study among a student sample (N = 257) the reliability and validity of the inventory were examined The internal consistencies of the developed scales were high, with the exception of Openmindedness and Flexibility. On the basis of factor analysis and the pattern of intercorrelations four reliable higher-level dimensions were distinguished: 'Openness', 'Emotional Stability','Social Initiative', and 'Flexibility'. The correlations between these dimensions find related instruments were in the expected direction. Moreover, the data supported the predictive value of the instrument of multicultural activity and its incremental value above the Big Five in predicting international or orientation and aspiration of an international career. The Multicultural Personality Questionnaire may be used as an instrument for the selection of expatriates or as re diagnostic tool for assessing further training needs. Copyright (C) 2000 John Wiley & Sons, Ltd.

Phantom pain and phantom sensations in upper limb amputees: an epidemiological study

Abstract: Phantom pain in subjects with an amputated limb is a well-known problem. However, estimates of the prevalence of phantom pain differ considerably in the literature. Various factors associated with phantom pain have been described including pain before the amputation, gender, dominance, and time elapsed since the amputation. The purposes of this study were to determine prevalence and factors associated with phantom pain and phantom sensations in upper limb amputees in The Netherlands. Additionally, the relationship between phantom pain, phantom sensations and prosthesis use in upper limb amputees was investigated. One hundred twenty-four upper limb amputees participated in this study. Subjects were asked to fill out a self-developed questionnaire scoring the following items: date, side, level, and reason of amputation, duration of experienced pain before amputation, frequencies with which phantom sensations, phantom pain, and stump pain are experienced, amount of trouble and suffering experienced, respectively, related to these sensations, type of phantom sensations, medical treatment received for phantom pain and/or stump pain, and the effects of the treatment, self medication, and prosthesis use. The response rate was 80%. The prevalence of phantom pain was 51%, of phantom sensations 76% and of stump pain 49%; 48% of the subjects experienced phantom pain a few times per day or more; 64% experienced moderate to very much suffering from the phantom pain. A significant association was found between phantom pain and phantom sensations (relative risk 11.3) and between phantom pain and stump pain (relative risk 1.9). No other factors associated with phantom pain or phantom sensations could be determined. Only four patients received medical treatment for their phantom pain. Phantom pain is a common problem in upper limb amputees that causes considerable suffering for the subjects involved. Only a minority of subjects are treated for phantom pain. Further research is needed to determine factors associated with phantom pain.

Prediction of relapses in Wegener's granulomatosis by measurement of antineutrophil cytoplasmic antibody levels: a prospective study.

Abstract: Objective. Prediction of relapses in Wegener's granulomatosis (WG) by measuring levels of antineutrophil cytoplasmic antibodies (ANCA) directed against proteinase 3 (PR3) or myeloperoxidase (MPO) remains a controversial issue. To assess the value of serial quantification of ANCA by indirect immunofluorescence (IIF) and antigen-specific enzyme-linked immunosorbent assay (ELISA) for monitoring disease activity in patients with WG, a prospective observational study was conducted in patients with WG attending an outpatient clinic in the Netherlands. Methods. One hundred patients with WG (85 with PR3-ANCA, 15 with MPO-ANCA) were studied prospectively from 1996 to 1998. Serum samples were obtained and analyzed every 2 months for ANCA levels. Disease activity was prospectively assessed without knowledge of the ANCA levels. Results. Relapses occurred in 37 of 100 patients (37%). Thirty-four (92%) of the 37 patients showed a rise in the level of ANCA preceding their relapse, as detected by ELISA or IIF. The predictive value of an increase in ANCA titers for relapse was 57% (17 of 30) for cytoplasmic/classic ANCA (cANCA; by IIF), 71% (27 of 38) for PR3-ANCA (by ELISA), and 100% (3 of 3) for MPO-ANCA (by ELISA). The predictive value of a rise in ANCA as measured by ELISA or IIF did not substantially improve following concomitant measurement of the IgG3 subclass of PR3-ANCA. Forty-three percent of patients who showed a rise in cANCA (by IIF) and 29% with a rise in PR3-ANCA (by ELISA) did not subsequently experience a relapse. Conclusion. Serial measurement of ANCA levels is valuable for the early prediction of relapses in patients with WG.

Eye Fixations on Advertisements and Memory for Brands: A Model and Findings

Abstract: The number of brands in the marketplace has vastly increased in the 1980s and 1990s, and the amount of money spent on advertising has run parallel. Print advertising is a major communication instrument for advertisers, but print media have become cluttered with advertisements for brands. Therefore, it has become difficult to attract and keep consumers' attention. Advertisements that fail to gain and retain consumers' attention cannot be effective, but attention is not sufficient: Advertising needs to leave durable traces of brands in memory. Eye movements are eminent indicators of visual attention. However, what is currently missing in eye movementresearch is a serious account of the processing that takes place to store information in long-term memory. We attempt to provide such an account through the development of a formal model. We model the process by which eye fixations on print advertisements lead to memory for the advertised brands, using a hierarchical Bayesian model, but, rather than postulating such a model as a mere data-analysis tool, we derive it from substantive theory on attention and memory. The model is calibrated to eye-movement data that are collected during exposure of subjects to ads in magazines, and subsequent recognition of the brand in a perceptual memory task. During exposure to the ads we record the frequencies of fixations on three ad elements; brand, pictorial and text and, during the memory task, the accuracy and latency of memory. Thus, the available data for each subject consist of the frequency of fixations on the ad elements and the accuracy and the latency of memory. The model that we develop is grounded in attention and memory theory and describes information extraction and accumulation during ad exposure and their effect on the accuracy and latency of brand memory. In formulating it, we assume that subjects have different eye-fixation rates for the different ad elements, because of which a negative binomial model of fixation frequency arises, and we specify the influence of the size of the ad elements. It is assumed that the number of fixations, not their duration, is related to the amount of information a consumer extracts from an ad. The information chunks extracted at each fixation are assumed to be random, varying across ads and consumers, and are estimated from the observed data. The accumulation of information across multiple fixations to the ad elements in long-term memory is assumed to be additive. The total amount of accumulated information that is not directly observed but estimated using our model influences both the accuracy and latency of subsequent brand memory. Accurate memory is assumed to occur when the accumulated information exceeds a threshold that varies randomly across ads and consumers in a binary probit-type of model component. The effect of two media-planning variables, the ad's serial position in a magazine and the ad's location on the double page, on the brand memory threshold are specified. We formulate hypotheses on the effects of ad element surface, serial position, and location. The model is applied in a study involving a sample of 88 consumers who were exposed to 65 print ads appearing in their natural context in two magazines. The frequency of eye fixations was recorded for each consumer and advertisement with infrared eye-tracking methodology. In a subsequent indirect memory task, consumers identified the brands from pixelated images of the ads. Across the two magazines, fixations to the pictorial and the brand systematically promote accurate brand memory, but text fixations do not. Brand surface has a particularly prominent effect. The more information is extracted from an ad during fixations, the shorter the latency of brand memory is. We find a systematic recency effect: When subjects are exposed to an ad later, they tend to identify it better. In addition, there is a small primacy effect. The effect of the ad's location on the right or left of the page depends on the advertising context. We show how the model supports advertising planning and testing and offer recommendations for further research on the effectiveness of brand communication. In future research the model may be extended to accommodate the effects of repeated exposure to ads, to further detail the representation of strength and association of memory, and to include the effects of creative tactics and media planning variables beyond the ones we included in the present study.

Hydrogen Bonding in DNA Base Pairs: Reconciliation of Theory and Experiment

Abstract: Up till now, there has been a significant disagreement between theory and experiment regarding hydrogen bond lengths in Watson−Crick base pairs. To investigate the possible sources of this discrepancy, we have studied numerous model systems for adenine−thymine (AT) and guanine−cytosine (GC) base pairs at various levels (i.e., BP86, PW91, and BLYP) of nonlocal density functional theory (DFT) in combination with different Slater-type orbital (STO) basis sets. Best agreement with available gas-phase experimental A−T and G−C bond enthalpies (−12.1 and −21.0 kcal/mol) is obtained at the BP86/TZ2P level, which (for 298 K) yields −11.8 and −23.8 kcal/mol. However, the computed hydrogen bond lengths show again the notorious discrepancy with experimental values. The origin of this discrepancy is not the use of the plain nucleic bases as models for nucleotides: the disagreement with experiment remains no matter if we use hydrogen, methyl, deoxyribose, or 5‘-deoxyribose monophosphate as the substituents at N9 and N...

Central Bank Independence: An Update of Theory and Evidence

Abstract: This paper reviews recent research on central bank independence (CBI). After we have distinguished between independence and conservativeness, the literature on optimal inflation contracts is discussed, followed by research in which the inflationary bias is endogenised. Finally, the various challenges that have been raised against previous empirical findings on CBI are reviewed. We conclude that the negative relationship between CBI and inflation is quite robust.

Mental fatigue and task control: planning and preparation.

Abstract: The effects of mental fatigue on planning and preparation for future actions were examined, using a task switching paradigm. Fatigue was induced by “time on task,” with subjects performing a switch task continuously for 2 hr. Subjects had to alternate between tasks on every second trial, so that a new task set was required on every second trial. Manipulations of response–stimulus intervals (RSIs) were used to examine whether subjects prepared themselves for the task change. Behavioral measurements, event-related potentials (ERPs), and mood questionnaires were used to assess the effects of mental fatigue. Reaction times (RTs) were faster on trials in which no change in task set was required in comparison with switch trials, requiring a new task set. Long RSIs were used efficiently to prepare for the processing of subsequent stimuli. With increasing mental fatigue, preparation processes seemed to become less adequate and the number of errors increased. A clear poststimulus parietal negativity was observed on repetition trials, which reduced with time on task. This attention-related component was less pronounced in switch trials; instead, ERPs elicited in switch trials showed a clear frontal negativity. This negativity was also diminished by time on task. ERP differences between repetition and switch trials became smaller with increasing time on task.

YidC, the Escherichia coli homologue of mitochondrial Oxa1p, is a component of the Sec translocase

Abstract: In Escherichia coli, both secretory and inner membrane proteins initially are targeted to the core SecYEG inner membrane translocase. Previous work has also identified the peripherally associated SecA protein as well as the SecD, SecF and YajC inner membrane proteins as components of the translocase. Here, we use a cross-linking approach to show that hydrophilic portions of a co-translationally targeted inner membrane protein (FtsQ) are close to SecA and SecY, suggesting that insertion takes place at the SecA/Y interface. The hydrophobic FtsQ signal anchor sequence contacts both lipids and a novel 60 kDa translocase-associated component that we identify as YidC. YidC is homologous to Saccharomyces cerevisiae Oxa1p, which has been shown to function in a novel export pathway at the mitochondrial inner membrane. We propose that YidC is involved in the insertion of hydrophobic sequences into the lipid bilayer after initial recognition by the SecAYEG translocase.

T-duality and actions for non-BPS D-branes

Abstract: We employ T-duality to restrict the tachyon dependence of effective actions for non-BPS D-branes. For the Born-Infeld part the criteria of T-duality and supersymmetry are satisfied by a simple extension of the D-brane Born-Infeld action.

Highly Enantioselective Rhodium-Catalyzed Hydrogenation with Monodentate Ligands

Abstract: The homogeneous enantioselective hydrogenation of functionalized prochiral olefins is one of the most frequently studied and most efficient transition metal-catalyzed reactions. In the first reports using chiral Wilkinson type catalysts, low enantiomeric excesses (ee’s) were obtained using monodentate phosphines as ligands. All attempts to develop monodentate ligands which would afford high ee’s in this reaction met with limited success, the best result being reached with CAMP, already published in 1972, giving ee’s up to 90% in the hydrogenation of dehydroamino acids. Although new monodentate phosphorus ligands play a significant role in other transition metal-catalyzed reactions, highly enantioselective hydrogenations are exclusively based on bidentate phosphorus ligands. Starting with Kagan’s diop a large number of bidentate ligands with excellent selectivities was designed. Among the most successful are DIPAMP, which gives superior results compared to its monodentate analogue PAMP, the frequently used BINAP ligand, the ferrocenyl-based ligands and the DuPHOS, BPE, and FerroTANE ligands, the latter showing extremely high enantioselectivities and broad scope. To date, not only phosphines (phosphanes) are used but also bidentate aminophosphines, phosphites, phosphinites, phosphonites, and hybrid ligands such as phosphine-phosphite, aminophosphine-phosphinite, and phosphine-phosphonite,

Biomarker evidence for widespread anaerobic methane oxidation in Mediterranean sediments by a consortium of methanogenic archaea and bacteria

Abstract: Although abundant geochemical data indicate that anaerobic methane oxidation occurs in marine sediments, the linkage to specific microorganisms remains unclear. In order to examine processes of methane consumption and oxidation, sediment samples from mud volcanoes at two distinct sites on the Mediterranean Ridge were collected via the submersible Nautile. Geochemical data strongly indicate that methane is oxidized under anaerobic conditions, and compound-specific carbon isotope analyses indicate that this reaction is facilitated by a consortium of archaea and bacteria. Specifically, these methane-rich sediments contain high abundances of methanogen-specific biomarkers that are significantly depleted in 13C (δ13C values are as low as −95‰). Biomarkers inferred to derive from sulfate-reducing bacteria and other heterotrophic bacteria are similarly depleted. Consistent with previous work, such depletion can be explained by consumption of 13C-depleted methane by methanogens operating in reverse and as part a consortium of organisms in which sulfate serves as the terminal electron acceptor. Moreover, our results indicate that this process is widespread in Mediterranean mud volcanoes and in some localized settings is the predominant microbiological process.