@article {1737, title = {Methane cycling. Nonequilibrium clumped isotope signals in microbial methane.}, journal = {Science}, volume = {348}, year = {2015}, month = {2015 Apr 24}, pages = {428-31}, abstract = {

Methane is a key component in the global carbon cycle, with a wide range of anthropogenic and natural sources. Although isotopic compositions of methane have traditionally aided source identification, the abundance of its multiply substituted "clumped" isotopologues (for example, (13)CH3D) has recently emerged as a proxy for determining methane-formation temperatures. However, the effect of biological processes on methane{\textquoteright}s clumped isotopologue signature is poorly constrained. We show that methanogenesis proceeding at relatively high rates in cattle, surface environments, and laboratory cultures exerts kinetic control on (13)CH3D abundances and results in anomalously elevated formation-temperature estimates. We demonstrate quantitatively that H2 availability accounts for this effect. Clumped methane thermometry can therefore provide constraints on the generation of methane in diverse settings, including continental serpentinization sites and ancient, deep groundwaters.

}, keywords = {Animals, Carbon Cycle, Carbon Isotopes, Cattle, Groundwater, Hydrogen, Methane, Methanomicrobiales, Temperature}, issn = {1095-9203}, doi = {10.1126/science.aaa4326}, author = {Wang, David T and Gruen, Danielle S and Lollar, Barbara Sherwood and Hinrichs, Kai-Uwe and Stewart, Lucy C and Holden, James F and Hristov, Alexander N and Pohlman, John W and Morrill, Penny L and K{\"o}nneke, Martin and Delwiche, Kyle B and Reeves, Eoghan P and Sutcliffe, Chelsea N and Ritter, Daniel J and Seewald, Jeffrey S and McIntosh, Jennifer C and Hemond, Harold F and Kubo, Michael D and Cardace, Dawn and Hoehler, Tori M and Ono, Shuhei} } @article {1206, title = {Hydrogen-limited growth of hyperthermophilic methanogens at deep-sea hydrothermal vents.}, journal = {Proc Natl Acad Sci U S A}, volume = {109}, year = {2012}, month = {2012 Aug 21}, pages = {13674-9}, abstract = {

Microbial productivity at hydrothermal vents is among the highest found anywhere in the deep ocean, but constraints on microbial growth and metabolism at vents are lacking. We used a combination of cultivation, molecular, and geochemical tools to verify pure culture H(2) threshold measurements for hyperthermophilic methanogenesis in low-temperature hydrothermal fluids from Axial Volcano and Endeavour Segment in the northeastern Pacific Ocean. Two Methanocaldococcus strains from Axial and Methanocaldococcus jannaschii showed similar Monod growth kinetics when grown in a bioreactor at varying H(2) concentrations. Their H(2) half-saturation value was 66 μM, and growth ceased below 17-23 μM H(2), 10-fold lower than previously predicted. By comparison, measured H(2) and CH(4) concentrations in fluids suggest that there was generally sufficient H(2) for Methanocaldococcus growth at Axial but not at Endeavour. Fluids from one vent at Axial (Marker 113) had anomalously high CH(4) concentrations and contained various thermal classes of methanogens based on cultivation and mcrA/mrtA analyses. At Endeavour, methanogens were largely undetectable in fluid samples based on cultivation and molecular screens, although abundances of hyperthermophilic heterotrophs were relatively high. Where present, Methanocaldococcus genes were the predominant mcrA/mrtA sequences recovered and comprised \~{}0.2-6\% of the total archaeal community. Field and coculture data suggest that H(2) limitation may be partly ameliorated by H(2) syntrophy with hyperthermophilic heterotrophs. These data support our estimated H(2) threshold for hyperthermophilic methanogenesis at vents and highlight the need for coupled laboratory and field measurements to constrain microbial distribution and biogeochemical impacts in the deep sea.

}, keywords = {Archaea, Biodiversity, Coculture Techniques, DNA, Ribosomal, Ecosystem, Gases, Geography, Hydrogen, Hydrothermal Vents, Kinetics, Methane, Molecular Sequence Data, Temperature, Time Factors, Water Microbiology}, issn = {1091-6490}, doi = {10.1073/pnas.1206632109}, author = {Ver Eecke, Helene C and Butterfield, David A and Huber, Julie A and Lilley, Marvin D and Olson, Eric J and Roe, Kevin K and Evans, Leigh J and Merkel, Alexandr Y and Cantin, Holly V and Holden, James F} } @article {1208, title = {Production of hydrogen from α-1,4- and β-1,4-linked saccharides by marine hyperthermophilic Archaea.}, journal = {Appl Environ Microbiol}, volume = {77}, year = {2011}, month = {2011 May}, pages = {3169-73}, abstract = {

Nineteen hyperthermophilic heterotrophs from deep-sea hydrothermal vents, plus the control organism Pyrococcus furiosus, were examined for their ability to grow and produce H$_{2}$ on maltose, cellobiose, and peptides and for the presence of the genes encoding proteins that hydrolyze starch and cellulose. All of the strains grew on these disaccharides and peptides and converted maltose and peptides to H$_{2}$ even when elemental sulfur was present as a terminal electron acceptor. Half of the strains had at least one gene for an extracellular starch hydrolase, but only P. furiosus had a gene for an extracellular β-1,4-endoglucanase. P. furiosus was serially adapted for growth on CF11 cellulose and H$_{2}$ production, which is the first reported instance of hyperthermophilic growth on cellulose, with a doubling time of 64 min. Cell-specific H$_{2}$ production rates were 29 fmol, 37 fmol, and 54 fmol of H$_{2}$ produced cell$^{-}${\textonesuperior} doubling$^{-}${\textonesuperior} on α-1,4-linked sugars, β-1,4-linked sugars, and peptides, respectively. The highest total community H$_{2}$ production rate came from growth on starch (2.6 mM H$_{2}$ produced h$^{-}${\textonesuperior}). Hyperthermophilic heterotrophs may serve as an important alternate source of H$_{2}$ for hydrogenotrophic microorganisms in low-H$_{2}$ hydrothermal environments, and some are candidates for H$_{2}$ bioenergy production in bioreactors.

}, keywords = {Archaea, Carbohydrate Metabolism, Hot Springs, Hydro-Lyases, Hydrogen, Peptides, Seawater}, issn = {1098-5336}, doi = {10.1128/AEM.01366-10}, author = {Oslowski, Daniel M and Jung, Jong-Hyun and Seo, Dong-Ho and Park, Cheon-Seok and Holden, James F} }