Secondary production and priming reshape the organic matter composition in marine sediments.

Organic matter (OM) transformations in marine sediments play a crucial role in the global carbon cycle. However, secondary production and priming have been ignored in marine biogeochemistry. By incubating shelf sediments with various C-labeled algal substrates for 400 days, we show that ~65% of the lipids and ~20% of the proteins were mineralized by numerically minor heterotrophic bacteria as revealed by RNA stable isotope probing.

Deglacial increase of seasonal temperature variability in the tropical ocean.

The relatively stable Holocene climate was preceded by a pronounced event of abrupt warming in the Northern Hemisphere, the termination of the Younger Dryas (YD) cold period. Although this transition has been intensively studied, its imprint on low-latitude ocean temperature is still controversial and its effects on sub-annual to decadal climate variability remain poorly understood. Sea surface temperature (SST) variability at these timescales in the tropical Atlantic is expected to intensify under current and future global warming and has considerable consequences for environmental conditions in Africa and South America, and for tropical Pacific climate.

Biogenic formation of amorphous carbon by anaerobic methanotrophs and select methanogens.

Elemental carbon exists in different structural forms including graphite, diamond, fullerenes, and amorphous carbon. In nature, these materials are produced through abiotic chemical processes under high temperature and pressure but are considered generally inaccessible to biochemical synthesis or breakdown. Here, we identified and characterized elemental carbon isolated from consortia of anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB), which together carry out the anaerobic oxidation of methane (AOM).

Macroalgae degradation promotes microbial iron reduction via electron shuttling in coastal Antarctic sediments.

Colonization of newly ice-free areas by marine benthic organisms intensifies burial of macroalgae detritus in Potter Cove coastal surface sediments (Western Antarctic Peninsula). Thus, fresh and labile macroalgal detritus serves as primary organic matter (OM) source for microbial degradation. Here, we investigated the effects on post-depositional microbial iron reduction in Potter Cove using sediment incubations amended with pulverized macroalgal detritus as OM source, acetate as primary product of OM degradation and lepidocrocite as reactive iron oxide to mimic in situ conditions.

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.

Crystalline iron oxides stimulate methanogenic benzoate degradation in marine sediment-derived enrichment cultures.

Elevated dissolved iron concentrations in the methanic zone are typical geochemical signatures of rapidly accumulating marine sediments. These sediments are often characterized by co-burial of iron oxides with recalcitrant aromatic organic matter of terrigenous origin. Thus far, iron oxides are predicted to either impede organic matter degradation, aiding its preservation, or identified to enhance organic carbon oxidation via direct electron transfer.

CO conversion to methane and biomass in obligate methylotrophic methanogens in marine sediments.

Methyl substrates are important compounds for methanogenesis in marine sediments but diversity and carbon utilization by methylotrophic methanogenic archaea have not been clarified. Here, we demonstrate that RNA-stable isotope probing (SIP) requires C-labeled bicarbonate as co-substrate for identification of methylotrophic methanogens in sediment samples of the Helgoland mud area, North Sea. Using lipid-SIP, we found that methylotrophic methanogens incorporate 60-86% of dissolved inorganic carbon (DIC) into lipids, and thus considerably more than what can be predicted from known metabolic pathways (~40% contribution).

Methanothermobacter thermautotrophicus modulates its membrane lipids in response to hydrogen and nutrient availability.

Methanothermobacter thermautotrophicus strain ΔH is a model hydrogenotrophic methanogen, for which extensive biochemical information, including the complete genome sequence, is available. Nevertheless, at the cell membrane lipid level, little is known about the responses of this archaeon to environmental stimuli. In this study, the lipid composition of M.

Real-time drilling mud gas monitoring for qualitative evaluation of hydrocarbon gas composition during deep sea drilling in the Nankai Trough Kumano Basin.

Background: Integrated Ocean Drilling Program Expedition 338 was the second scientific expedition with D/V Chikyu during which riser drilling was conducted as part of the Nankai Trough Seismogenic Zone Experiment. Riser drilling enabled sampling and real-time monitoring of drilling mud gas with an onboard scientific drilling mud gas monitoring system ("SciGas"). A second, independent system was provided by Geoservices, a commercial mud logging service.

Thermococcus kodakarensis modulates its polar membrane lipids and elemental composition according to growth stage and phosphate availability.

We observed significant changes in the elemental and intact polar lipid (IPL) composition of the archaeon Thermococcus kodakarensis (KOD1) in response to growth stage and phosphorus supply. Reducing the amount of organic supplements and phosphate in growth media resulted in significant decreases in cell size and cellular quotas of carbon (C), nitrogen (N), and phosphorus (P), which coincided with significant increases in cellular IPL quota and IPLs comprising multiple P atoms and hexose moieties. Relatively more cellular P was stored as IPLs in P-limited cells (2-8%) compared to control cells (<0.