Temperature limits to deep subseafloor life in the Nankai Trough subduction zone.

Microorganisms in marine subsurface sediments substantially contribute to global biomass. Sediments warmer than 40°C account for roughly half the marine sediment volume, but the processes mediated by microbial populations in these hard-to-access environments are poorly understood. We investigated microbial life in up to 1.2-kilometer-deep and up to 120°C hot sediments in the Nankai Trough subduction zone. Above 45°C, concentrations of vegetative cells drop two orders of magnitude and endospores become more than 6000 times more abundant than vegetative cells. Methane is biologically produced and oxidized until sediments reach 80° to 85°C. In 100° to 120°C sediments, isotopic evidence and increased cell concentrations demonstrate the activity of acetate-degrading hyperthermophiles. Above 45°C, populated zones alternate with zones up to 192 meters thick where microbes were undetectable.

Global diversity of microbial communities in marine sediment.

Microbial life in marine sediment contributes substantially to global biomass and is a crucial component of the Earth system. Subseafloor sediment includes both aerobic and anaerobic microbial ecosystems, which persist on very low fluxes of bioavailable energy over geologic time. However, the taxonomic diversity of the marine sedimentary microbial biome and the spatial distribution of that diversity have been poorly constrained on a global scale. We investigated 299 globally distributed sediment core samples from 40 different sites at depths of 0.1 to 678 m below the seafloor. We obtained ∼47 million 16S ribosomal RNA (rRNA) gene sequences using consistent clean subsampling and experimental procedures, which enabled accurate and unbiased comparison of all samples. Statistical analysis reveals significant correlations between taxonomic composition, sedimentary organic carbon concentration, and presence or absence of dissolved oxygen. Extrapolation with two fitted species-area relationship models indicates taxonomic richness in marine sediment to be 7.85 × 103 to 6.10 × 105 and 3.28 × 104 to 2.46 × 106 amplicon sequence variants for Archaea and Bacteria, respectively. This richness is comparable to the richness in topsoil and the richness in seawater, indicating that Bacteria are more diverse than Archaea in Earth's global biosphere.

Saline Contrast Transesophageal Echocardiography in Fontan Patients: Assessment of the Presence, Type, and Size of Right to Left Shunts.

Right to left (R-L) shunts resulting in cyanosis or systemic embolization occur after the Fontan procedure. The primary modality of diagnosing these is angiography. Successful delineation of these shunts in Fontan patients using selective saline contrast transesophageal echocardiography (SCTEE) may allow for reduced radiation and contrast exposure. We hypothesized that SCTEE could accurately determine the presence, type, and semiquantitative shunt size of R-L shunts in Fontan patients. SCTEE was performed in Fontan patients undergoing angiography for clinical indications. Injections were performed in six sites: mid-Fontan, right and left pulmonary arteries, superior and inferior vena cavae, and innominate vein. R-L shunt size was subjectively graded as 0 = absent, 1 = small, and 2 = medium or large based on echo contrast density in the left atrium. SCTEE was compared to angiography. 33 patients with Fontan were studied with median age 15 years, median weight 50.1 kg, and median O2 saturation of 90% in the R-L shunt group and 95% in the no R-L shunt group. R-L shunt types included intracardiac shunts (ICS), veno-venous collaterals (VVCs), arteriovenous malformations (AVMs), and their combinations. SCTEE versus angiography results were the same for the presence, type, and size of R-L shunts in 79% (26/33). SCTEE identified shunts in 88% (29/33). Angiography identified shunts in 85% (28/33). Neither method missed any medium or large R-L shunts. SCTEE and angiography had similar accuracy. SCTEE accurately detected the presence, type, and size of R-L shunts in most Fontan patients in this study. This can be used to guide targeted angiography, reducing radiation exposure and contrast load.

Microbial dormancy in the marine subsurface: Global endospore abundance and response to burial.

Marine sediments host an unexpectedly large microbial biosphere, suggesting unique microbial mechanisms for surviving burial and slow metabolic turnover. Although dormancy is generally considered an important survival strategy, its specific role in subsurface sediments remains unclear. We quantified dormant bacterial endospores in 331 marine sediment samples from diverse depositional types and geographical origins. The abundance of endospores relative to vegetative cells increased with burial depth and endospores became dominant below 25 m, with an estimated population of 2.5 × 1028 to 1.9 × 1029 endospores in the uppermost kilometer of sediment and a corresponding biomass carbon of 4.6 to 35 Pg surpassing that of vegetative cells. Our data further identify distinct endospore subgroups with divergent resistance to burial and aging. Endospores may shape the deep biosphere by providing a core population for colonization of new habitats and/or through low-frequency germination to sustain slow growth in this environment.

Deep-biosphere methane production stimulated by geofluids in the Nankai accretionary complex.

Microbial life inhabiting subseafloor sediments plays an important role in Earth's carbon cycle. However, the impact of geodynamic processes on the distributions and carbon-cycling activities of subseafloor life remains poorly constrained. We explore a submarine mud volcano of the Nankai accretionary complex by drilling down to 200 m below the summit. Stable isotopic compositions of water and carbon compounds, including clumped methane isotopologues, suggest that ~90% of methane is microbially produced at 16° to 30°C and 300 to 900 m below seafloor, corresponding to the basin bottom, where fluids in the accretionary prism are supplied via megasplay faults. Radiotracer experiments showed that relatively small microbial populations in deep mud volcano sediments (102 to 103 cells cm-3) include highly active hydrogenotrophic methanogens and acetogens. Our findings indicate that subduction-associated fluid migration has stimulated microbial activity in the mud reservoir and that mud volcanoes may contribute more substantially to the methane budget than previously estimated.

Acquired Cor Triatriatum Sinister After the Fontan Operation and Successful Resection in a Child.

Cor triatriatum sinister is a rare congenital lesion encountered in children. It consists of a fibromuscular membrane that separates the left atrium into two chambers resulting in a triatrial heart and often occurs with other structural cardiac anomalies. The acquired form is uncommon and has only been reported after orthotopic heart transplantation or as a complication of infective endocarditis in adults. These cases were mostly because of hypertrophied atrial tissue or suture lines and torsion of the atrium. We describe the first case of acquired cor triatriatum late after the Fontan procedure with successful surgical resection in a child.

Microbial Sulfate Reduction Potential in Coal-Bearing Sediments Down to ~2.5 km below the Seafloor off Shimokita Peninsula, Japan.

Sulfate reduction is the predominant anaerobic microbial process of organic matter mineralization in marine sediments, with recent studies revealing that sulfate reduction not only occurs in sulfate-rich sediments, but even extends to deeper, methanogenic sediments at very low background concentrations of sulfate. Using samples retrieved off the Shimokita Peninsula, Japan, during the Integrated Ocean Drilling Program (IODP) Expedition 337, we measured potential sulfate reduction rates by slurry incubations with 35S-labeled sulfate in deep methanogenic sediments between 1276.75 and 2456.75 meters below the seafloor. Potential sulfate reduction rates were generally extremely low (mostly below 0.1 pmol cm-3 d-1) but showed elevated values (up to 1.8 pmol cm-3 d-1) in a coal-bearing interval (Unit III). A measured increase in hydrogenase activity in the coal-bearing horizons coincided with this local increase in potential sulfate reduction rates. This paired enzymatic response suggests that hydrogen is a potentially important electron donor for sulfate reduction in the deep coalbed biosphere. By contrast, no stimulation of sulfate reduction rates was observed in treatments where methane was added as an electron donor. In the deep coalbeds, small amounts of sulfate might be provided by a cryptic sulfur cycle. The isotopically very heavy pyrites (δ34S = +43‰) found in this horizon is consistent with its formation via microbial sulfate reduction that has been continuously utilizing a small, increasingly 34S-enriched sulfate reservoir over geologic time scales. Although our results do not represent in-situ activity, and the sulfate reducers might only have persisted in a dormant, spore-like state, our findings show that organisms capable of sulfate reduction have survived in deep methanogenic sediments over more than 20 Ma. This highlights the ability of sulfate-reducers to persist over geological timespans even in sulfate-depleted environments. Our study moreover represents the deepest evidence of a potential for sulfate reduction in marine sediments to date.

Hydrogen Utilization Potential in Subsurface Sediments.

Subsurface microbial communities undertake many terminal electron-accepting processes, often simultaneously. Using a tritium-based assay, we measured the potential hydrogen oxidation catalyzed by hydrogenase enzymes in several subsurface sedimentary environments (Lake Van, Barents Sea, Equatorial Pacific, and Gulf of Mexico) with different predominant electron-acceptors. Hydrogenases constitute a diverse family of enzymes expressed by microorganisms that utilize molecular hydrogen as a metabolic substrate, product, or intermediate. The assay reveals the potential for utilizing molecular hydrogen and allows qualitative detection of microbial activity irrespective of the predominant electron-accepting process. Because the method only requires samples frozen immediately after recovery, the assay can be used for identifying microbial activity in subsurface ecosystems without the need to preserve live material. We measured potential hydrogen oxidation rates in all samples from multiple depths at several sites that collectively span a wide range of environmental conditions and biogeochemical zones. Potential activity normalized to total cell abundance ranges over five orders of magnitude and varies, dependent upon the predominant terminal electron acceptor. Lowest per-cell potential rates characterize the zone of nitrate reduction and highest per-cell potential rates occur in the methanogenic zone. Possible reasons for this relationship to predominant electron acceptor include (i) increasing importance of fermentation in successively deeper biogeochemical zones and (ii) adaptation of H2ases to successively higher concentrations of H2 in successively deeper zones.