Microbial dimethylsulfide (DMS) degradation in anoxic sediments

Dimethylsulfide (DMS) is the most abundant biogenic organosulfur compound emitted into the atmosphere. In anoxic sediments, DMS degradation leads to methane, a potent greenhouse gas. Alongside methanogens, sulfate-reducing bacteria (SRB) also degrade DMS, depending on sulfate availability. However, little is known about DMS degradation in anoxic sediments. This PhD aimed to explore the potential for DMS-dependent methane production and the diversity and metabolism of DMS-degrading microorganisms in anoxic sediments. Sediment was sampled along the salinity gradient of the Medway Estuary to understand how sulfate concentrations affect DMS-dependent methanogenesis. Sediment was also collected from rivers, important contributors to the global methane budget. Furthermore, we studied DMS degradation in the Baltic Sea following a phytoplankton bloom, which releases dimethylsulfoniopropionate, a major DMS precursor. The sediment samples were incubated with DMS as the only carbon and energy source. The methanogen and SRB diversities were analysed using taxonomic (16S rRNA) and functional genes (mcrA, dsrB). Samples from the Baltic Sea incubations were also selected for metagenomics and metatranscriptomics analyses. Results showed a 39%-92% methane yield from DMS in all sediment samples, indicating a high potential for DMS-dependent methanogenesis in anoxic sediments regardless of sulfate availability. Methanomethylovorans, Methanococcoides and Methanolobus were the most dominant DMS-degrading methanogens depending on sediment salinity, implying niche-partitioning likely driven by sulfate concentrations. In addition, DMS degradation initiated sulfate recycling in all low-sulfate incubations, thus affecting the sulfur cycle. Lastly, metagenomics and metatranscriptomics analyses showed for the first time that DMS could be degraded via the activity of trimethylamine and methanol methyltransferases rather than previously characterised DMS methyltransferases. This PhD project is the first cultivation-independent study of DMS-degrading microorganisms in anoxic sediments. It highlights the significance of anaerobic DMS degradation for global methane production and the carbon and sulfur cycles

Statistical analysis of maritime accidents of tankers 5000-20000 DWT

154 σ.Στην εργασία ασχολήθηκα με την στατιστική μελέτη και ανάλυση των ατυχημάτων πλοίων tanker μεγέθους dwt 5000-20000 ton κατά τη χρονική περίοδο 1990-2003. Τα ατυχήματα αυτά τα χωρίζουμε στις παρακάτω εννέα κατηγορίες: -ατυχήματα σύγκρουσης πλοίων -ατυχήματα επαφής πλοίων -ατυχήματα προσάραξης -ατυχήματα έκρηξης -ατυχήματα φωτιάς -ατυχήματα μη ατυχηματικής κατασκευαστικής αστοχίας -ατυχήματα αστοχίας εξαρτημάτων και εξοπλισμού του πλοίου -ατυχήματα αστοχίας μηχανικών εξαρτημάτων του πλοίου -ατυχήματα αγνώστων αιτιών Στην ανάλυση αυτή παρουσιάζονται οι έξι πρώτες κατηγορίες καθώς ατυχήματα τέτοιου τύπου είναι πιο πιθανόν να οδηγήσουν σε δυνητική απώλεια υδατοστεγούς ακεραιότητας του πλοίου και σε διαρροή πετρελαίου στο θαλάσσιο περιβάλλον. Επίσης έγινε μια σύντομη αναφορά της νομοθεσίας που αφορά στην πρόληψη της ρύπανσης η οποία προκαλέιται από τα ατυχήματα των πλοίων καθώς και μια σύγκριση πλοίων μονού τοιχώματος και πλοίων διπλού τοιχώματος. Στη συνέχεια, γίνεται μια περιγραφή του σημαντικότερου ατυχήματος δεξαμενόπλοιου αντίστοιχου μεγέθους. Επιπλέον, σε παράρτημα που παρατίθεται γίνεται μια εκτενής περιγραφή της βάσης δεδομένων των ατυχημάτων όσον αφορά στη λειτουργία και στον χειρισμό της. Η ανάλυση των ατυχημάτων αρχικά γίνεται ξεχωριστά για κάθε μία από τις παραπάνω έξι κατηγορίες, δίνοντας έμφαση στον τόπο και τις συνθήκες στις οποίες έλαβε χώρα το ατύχημα, στον τύπο της γάστρας του εκάστοτε πλοίου αλλά και στη μόλυνση που προκλήθηκε. Στο τέλος γίνεται ανάλυση των συγκεντρωτικών αποτελεσμάτων αλλά και σύγκριση αυτών με αντίστοιχες μελέτες για δεξαμενόπλοια μεγαλύτερου μεγέθους.In the project I made a statistical analysis of maritime incidents of tankers 5000-2000 dwt, concerning the period 1990-2003. The accidents that participated in the study can be categorized as follows: -Collision incidents -Contact incidents -Grounding incidents -Explosion incidents -Fire incidents -Non Accidental Structural Failure incidents -Hull Fitting incidents -Machinery Failure incidents -Unknown Reason incidents. In the following analysis, the six first categories are presented since these kind of incidents are more likely to lead in LOss of Watertight Integrity (LOWI) and Oil Spill in the maritrime environment. There is also a short reference to the legislation that has to do with the prevention of pollution from the accidents of ships. Moreover, there is a short text doing a comparison between single hull and double hull tankers. After that, the most important incident of this specific size category is being described. In addition to the above there is an annex of the database that has been used during the analysis, where there is a detailed description of the right way to be used by the analyst. The analysis of the incidents is firstly presented separately for each one of the six categories, with emphasis to the location and the conditions of the incident, the hull type and the pollution the incident caused each time. In the end, there is total and concentrated analysis of the results and a very useful comparison to the results of past similar studies and projects for larger tankers.Ευαγγελία Σ. Τσόλ

Diversity of dimethylsulfide‐degrading methanogens and sulfate‐reducing bacteria in anoxic sediments along the Medway Estuary, UK

Methane is a powerful greenhouse gas but the microbial diversity mediating methylotrophic methanogenesis is not well-characterized. One overlooked route to methane is via the degradation of dimethylsulfide (DMS), an abundant organosulfur compound in the environment. Methanogens and sulfate-reducing bacteria (SRB) can degrade DMS in anoxic sediments depending on sulfate availability. However, we know little about the underlying microbial community and how sulfate availability affects DMS degradation in anoxic sediments. We studied DMS-dependent methane production along the salinity gradient of the Medway Estuary (UK) and characterized, for the first time, the DMS-degrading methanogens and SRB using cultivation-independent tools. DMS metabolism resulted in high methane yield (39%–42% of the theoretical methane yield) in anoxic sediments regardless of their sulfate content. Methanomethylovorans, Methanolobus and Methanococcoides were dominant methanogens in freshwater, brackish and marine incubations respectively, suggesting niche-partitioning of the methanogens likely driven by DMS amendment and sulfate concentrations. Adding DMS also led to significant changes in SRB composition and abundance in the sediments. Increases in the abundance of Sulfurimonas and SRB suggest cryptic sulfur cycling coupled to DMS degradation. Our study highlights a potentially important pathway to methane production in sediments with contrasting sulfate content and sheds light on the diversity of DMS degraders

Methanolobus use unspecific methyltransferases to produce methane from dimethylsulphide in Baltic Sea sediments.

BACKGROUND: In anoxic coastal and marine sediments, degradation of methylated compounds is the major route to the production of methane, a powerful greenhouse gas. Dimethylsulphide (DMS) is the most abundant biogenic organic sulphur compound in the environment and an abundant methylated compound leading to methane production in anoxic sediments. However, understanding of the microbial diversity driving DMS-dependent methanogenesis is limited, and the metabolic pathways underlying this process in the environment remain unexplored. To address this, we used anoxic incubations, amplicon sequencing, genome-centric metagenomics and metatranscriptomics of brackish sediments collected along the depth profile of the Baltic Sea with varying sulphate concentrations. RESULTS: We identified Methanolobus as the dominant methylotrophic methanogens in all our DMS-amended sediment incubations (61-99%) regardless of their sulphate concentrations. We also showed that the mtt and mta genes (trimethylamine- and methanol-methyltransferases) from Methanolobus were highly expressed when the sediment samples were incubated with DMS. Furthermore, we did not find mtsA and mtsB (methylsulphide-methyltransferases) in metatranscriptomes, metagenomes or in the Methanolobus MAGs, whilst mtsD and mtsF were found 2-3 orders of magnitude lower in selected samples. CONCLUSIONS: Our study demonstrated that the Methanolobus genus is likely the key player in anaerobic DMS degradation in brackish Baltic Sea sediments. This is also the first study analysing the metabolic pathways of anaerobic DMS degradation in the environment and showing that methylotrophic methane production from DMS may not require a substrate-specific methyltransferase as was previously accepted. This highlights the versatility of the key enzymes in methane production in anoxic sediments, which would have significant implications for the global greenhouse gas budget and the methane cycle. Video Abstract

The Utilisation of INR to identify coagulopathy in burn patients.

Studies conflict on the significance of burn-induced coagulopathy. We posit that burn-induced coagulopathy is associated with injury severity in burns. Our purpose was to characterize coagulopathy profiles in burns and determine relationships between % total burn surface area (TBSA) burned and coagulopathy using the International Normalized Ratio (INR). Burned patients with INR values were identified in the TriNetX database and analyzed by %TBSA burned. Patients with history of transfusions, chronic hepatic failure, and those on anticoagulant medications were excluded. Interquartile ranges for INR in the burned study population were 1.2 (1.0-1.4). An INR of ≥ 1.5 was used to represent those with burn-induced coagulopathy as it fell outside the 3rd quartile. The population was stratified into subgroups using INR levels <1.5 or ≥1.5 on the day of injury. Data are average ± SD analyzed using chi-square; p < .05 was considered significant. There were 7,364 burned patients identified with INR <1.5, and 635 had INR ≥1.5. Comparing TBSA burned groups, burn-induced coagulopathy significantly increased in those with ≥20% TBSA; p = .048 at 20-29% TBSA, p = .0005 at 30-39% TBSA, and p < .0001 for 40% TBSA and above. Age played a significant factor with average age for those with burn-induced coagulopathy 59 ± 21.5 years and 46 ± 21.8 for those without (p < .0001). After matching for age, TBSA, and demographics, the risk of 28 day-mortality was higher in those with burn-induced coagulopathy compared to those without (risk difference 20.9%, p < .0001) and the odd ratio with 95% CI is 4.45 (3.399-5.825). Investigation of conditions associated with burn-induced coagulopathy showed the effect of heart diseases to be significant; 53% of patients with burn-induced coagulopathy had hypertension (p < .0001). Burn-induced coagulopathy increases with %TBSA burned. The information gained firmly reflects a link between %TBSA and burn-induced coagulopathy, which could be useful in prognosis and treatment decisions