Chemical signature of magnetotactic bacteria

There are longstanding and ongoing controversies about the abiotic or biological origin of nanocrystals of magnetite. On Earth, magnetotactic bacteria perform biomineralization of intracellular magnetite nanoparticles under a controlled pathway. These bacteria are ubiquitous in modern natural environments. However, their identification in ancient geological material remains challenging. Together with physical and mineralogical properties, the chemical composition of magnetite was proposed as a promising tracer for bacterial magnetofossil identification, but this had never been explored quantitatively and systematically for many trace elements. Here, we determine the incorporation of 34 trace elements in magnetite in both cases of abiotic aqueous precipitation and of production by the magnetotactic bacterium Magnetospirillum magneticum strain AMB-1. We show that, in biomagnetite, most elements are at least 100 times less concentrated than in abiotic magnetite and we provide a quantitative pattern of this depletion. Furthermore, we propose a previously unidentified method based on strontium and calcium incorporation to identify magnetite produced by magnetotactic bacteria in the geological record.Magnetite (Fe₃O₄) is a widespread iron oxide found in geological sedimentary deposits such as banded iron formations, carbonate platforms, or paleosols (1). It can be produced through abiotic or biotic pathways. Magnetotactic bacteria (MTB) and dissimilatory iron-reducing bacteria are known to synthetize magnetite nanoparticles (2).MTB are magnetite- or greigite (Fe₃S₄)-producing bacteria found in both freshwater and marine environments. They inhabit the oxic–anoxic transition zone under microaerophilic conditions required for their growth. Magnetite or greigite crystals are actively precipitated through biological mechanisms in intracellular organelles called magnetosomes (e.g., refs. 3 and 4). Magnetosomes are assembled in chains inside the cell (Fig. 1) and provide the microorganism with a permanent magnetic dipole. This arrangement allows the bacteria to align themselves along the Earth’s geomagnetic field and to reach the optimal position along vertical chemical gradients (5, 6). When the cell dies, magnetosomes may be deposited and trapped into sediments. Magnetite can then be fossilized if the redox conditions are appropriate (1). This mineral may thus be an indirect bacterial fossil. Magnetotactic bacteria have been proposed to represent one of the most ancient biomineralizing organisms (1, 7). Thus, the identification of fossil magnetotactic bacteria, hereafter named bacterial magnetofossils, would provide strong constraints on the evolution of life and of biomineralization over geological times.Open in a separate windowFig. 1.Transmission electron microscopy images of (A) bacteria cultivated in bottles and (B) in fermentor, (C) extracted chain of magnetosomes, (D) magnetosomes treated with SDS-Triton-phenol preparation, (E) bacterial magnetite leached with EDTA, and (F) untreated magnetosome. Extracted magnetosomes display chain structures assembled by magnetosome membranes and proteins (arrows in C). In contrast with magnetite treated with SDS-Triton-phenol (E), untreated magnetosomes show traces of organic matter (arrow in F). Once treated, magnetite from AMB-1 agglomerated, as shown in D. We also observed such agglomeration in abiotic magnetite. Magnetite did not seem to be affected by EDTA leaching.Magnetite produced by MTB shows highly controlled crystallographic structure (8). It displays narrow size distributions and is in the magnetic stable single-domain range. Magnetosome chains have remarkable magnetic properties (5, 6, 9), which have been used to identify bacterial magnetofossils in sediments. Although previous studies demonstrated that observations by electron microscopy and/or magnetic measurements could detect bacterial magnetofossils in natural samples (9–13), the chain structure is generally lost during sediment aging owing to degradation of organic matter assembling magnetosomes (9, 14). This strongly complicates the identification of the bacterial magnetofossils. Moreover, those magnetites undergo variable transformations ranging from isomorphic conversion to maghemite, all the way to crystals that just barely preserve the structural integrity (15). Thus, for bacterial magnetofossil identification in ancient rock samples reliable biosignatures surviving these modifications are still needed for distinguishing biogenic from abiotic magnetite (1, 2).Geochemical fingerprints can be used as a potential tool for identifying fossilized biominerals (2, 16). For instance, chemical purity has been suggested as a common feature of minerals produced by living organisms (2). The chemical purity of magnetite from MTB has been discussed for many years (e.g., ref. 17). Although not without controversy, it was suggested that low concentrations in minor elements observed in magnetite from Martian meteorite {"type":"entrez-protein","attrs":{"text":"ALH84001","term_id":"937293154","term_text":"ALH84001"}}ALH84001 could indicate a biological origin for magnetite (18). This interpretation was supported by abiotic formation of magnetite in the laboratory, leading to high levels of elements other than iron in the crystal products (19, 20), except if initial materials highly depleted in doping elements were used (21). However, the degree of magnetite chemical purity in these previous studies was estimated by energy dispersive x-ray spectroscopy (EDXS) coupled with transmission electron microscopy, which is usually limited to the quantification of relatively elevated elemental concentrations, typically higher than 0.1–1% (22). Moreover, EDXS analyses have been used to evaluate single-element incorporations into magnetite crystals produced by MTB (23–26). These experiments tested only high element concentrations, which may not be representative of natural conditions. A detailed measurement of the low levels of trace elements likely present in trace amounts in magnetite from MTB, together with the knowledge of the concentrations of these elements in the surrounding fluids, thus remain to be established. Indeed, rather than the low or high level of impurity in the magnetite, the important point would be to establish whether differential incorporation of elements exists between biotic and abiotic magnetites. In this work, we thus determined multielement partitioning between aqueous solution and either abiotic magnetite or magnetite from magnetosomes to provide reliable signatures of biological origin.Abiotic magnetite nanoparticles were synthetized in adapting previous work (27) by mixing Fe³⁺ and Fe²⁺ to which were added 34 trace elements at concentrations of 100 ppb of each element by weight in the solution. This magnetite chemical precipitation is related to an extensive previous literature reporting studies designed for decontamination of wastewaters (e.g., refs. 28 and 29). Our experiments were performed in a glove box to prevent Fe(II) and magnetite oxidation. Biomagnetite was produced from Magnetospirillum magneticum strain AMB-1 (ATCC700264) under two different conditions: (i) in a fermentor as described in ref. 30 and (ii) in bottles following ATCC recommendations. The initial growth media of the two experiments were different. In contrast with bottle cultures, pH and pO₂ were maintained constant in the fermentor and the medium was continuously homogenized by stirring. These contrasting conditions allow us to evaluate the variability possibly induced by the biosynthesis. In either case, the bacterial growth medium was doped with the same 34 trace elements at 100 ppb each, (i.e., at the same doping level as in the abiotic syntheses). Chains of magnetosomes were extracted from cells with a high-pressure homogenizer. Magnetosome membranes surrounding magnetite were removed using a Triton-SDS-phenol solution heated at 70 °C overnight. Magnetite nanoparticles were leached with ultrapure water and contaminant-free EDTA solution to chelate and remove any element adsorbed on mineral surface (Fig. 1). Abiotic and biotic bottle experiments were carried out in duplicate. Mineralogical characterization (i.e., size, shape, and structure) of the magnetite samples was obtained from X-ray diffraction and transmission electron microscopy (Fig. 1 and Fig. S1). The element concentrations in all experimental products were measured by high-resolution inductively coupled plasma mass spectrometry.     

Cholangite tuberculeuse simulant une maladie de Caroli : difficultés diagnostiques

Abstract

The liver and the bile ducts represent an exceptional location of tuberculosis. The clinical symptomatology is not specific.We describe three aspects macronodular, micronodular and canalicular which are the rarest.

Purpose

Precise the diagnostic difficulties of this entity insisting on the clinical, biological and morphological signs.

Case report

We report the case of 70 year old man without medical history, admitted for a clinicobiological cholangitis syndrome evolving in a context of impaired general condition. Acute cholecystitis was documented by ultrasound with a moderate dilatationof the common hepatic duct. The bili-MRI showed a dilation of the left intrahepatic bile ducts suggestive of Caroli’s disease. A bi-segmentectomy were performed. Histological examination finds a hepatic tuberculosis and infirm the diagnosis of Caroli’s disease.

Conclusion

Tuberculous cholangitis is rare and poses a diagnostic problem. It can simulate a Caroli disease leading to an unnecessary liver resection. Percutaneous liver biopsy can help to rectify the diagnosis for TBC.     

The effect of thrombolysis on short-term improvement depends on initial stroke severity

A large number of parameters have been identified as predictors of early outcome in patients with acute ischemic stroke. In the present work we analyzed a wide range of demographic, metabolic, physiological, clinical, laboratory and neuroimaging parameters in a large population of consecutive patients with acute ischemic stroke with the aim of identifying independent predictors of the early clinical course. We used prospectively collected data from the Acute Stroke Registry and Analysis of Lausanne. All consecutive patients with ischemic stroke admitted to our stroke unit and/or intensive care unit between 1 January 2003 and 12 December 2008 within 24 h after last-well time were analyzed. Univariate and multivariate analyses were performed to identify significant associations with the National Institute of Health Stroke Scale (NIHSS) score at admission and 24 h later. We also sought any interactions between the identified predictors. Of the 1,730 consecutive patients with acute ischemic stroke who were included in the analysis, 260 (15.0%) were thrombolyzed (mostly intravenously) within the recommended time window. In multivariate analysis, the NIHSS score at 24 h after admission was associated with the NIHSS score at admission (β = 1, p < 0.001), initial glucose level (β = 0.05, p < 0.002) and thrombolytic intervention (β = −2.91, p < 0.001). There was a significant interaction between thrombolysis and the NIHSS score at admission (p < 0.001), indicating that the short-term effect of thrombolysis decreases with increasing initial stroke severity. Thrombolytic treatment, lower initial glucose level and lower initial stroke severity predict a favorable early clinical course. The short-term effect of thrombolysis appears mainly in minor and moderate strokes, and decreases with increasing initial stroke severity.     

Impact of body mass index on hepatocellular carcinoma recurrence after liver transplantation through long-term follow-up

BackgroundObesity is associated with increased oncological risk and outcomes but the evidence surrounding the effect of body mass index (BMI) on increased risk of hepatocellular carcinoma (HCC) recurrence after liver transplantation (LT) is still questionable. The purpose of this retrospective study of a large cohort of adult patients transplanted for HCC was to investigate the effect of BMI on the incidence of HCC recurrence and outcome.MethodsData from 427 adult recipients transplanted for HCC between 2000 and 2017 were collected. Patients were classified at time of LT according to the World Health Organization BMI classification into 3 groups; group 1: BMI <25 (n=166), group 2: BMI 25–29.9 (n=150) and group 3: BMI ≥30 (n=111).ResultsThere were no significant changes of mean BMI overtime 26.8±5.0 kg/m2 at time of LT and 28.8±23.1 at 5 years. The recurrence rates of HCC after LT in the three groups were 19%, 16% and 17% respectively. The 5, 10 and 15-year recurrence free survival (RFS) rates were respectively 68.6%, 47.3% and 40.8% in group 1, 73.3%, 66.2% and 49.5% in group 2 and 68.8%, 57.5% and 47.7% in group 3 (log rank P=0.47).ConclusionsRecipient BMI at time of transplant and during follow-up didn’t impact the incidence of HCC recurrence nor long-term patient survival, irrespective to the status of the patients and their tumor characteristic at time of LT. The present study clearly confirms that obesity should not be considered, when selecting patients with HCC to LT, as a predictive factor of recurrence.     

Rotational excitation of C2H− anion in collision with H2

The discovery of anions in the interstellar medium has shown that they are very reactive species. This gave them great importance in the modeling of the chemical and astrophysical evolution of the interstellar medium. The detection of the first anion C₆H⁻ followed by the other anions C₄H⁻, C₈H⁻ and CN⁻ in the interstellar medium has encouraged research on other detectable anions. The C₂H⁻ anion was observed for the first time in the circumstellar envelope of IRC+10216 and in TMC-1. In these cold and low-density regions, precise modeling of the chemical and physical conditions of the observed emission lines requires knowledge of the radiative and collisional excitation rates. We present here the first new two-dimensional Potential Energy Surface (PES) for C₂H–H₂ interaction. Rotational excitation of the anion by collision with para-H₂(j_H2 = 0) is investigated. The PES is obtained in the super-molecular approach based on a single and double excitation coupled cluster method with perturbative contributions from triple excitations (CCSD(T)). In all our calculations, all atoms were described using the augmented correlation-consistent triple zeta (aug-cc-pVTZ) basis sets and bond f unctions. Fully-quantum close-coupling calculations of inelastic integral cross sections are done on a grid of collision energies large enough to ensure converged state-to-state rate coefficients for the 16 first rotational levels of C₂H⁻ and for temperatures ranging from 5 to 120 K. For this collisional system, rate coefficients exhibit a strong propensity in favor of even Δj transitions.

The discovery of anions in the interstellar medium has shown that they are very reactive species.