Person: Adams, Melissa Marie
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Adams
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Melissa Marie
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Adams, Melissa Marie
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Publication Anaerobic Methane Oxidation in Metalliferous Hydrothermal Sediments: Influence on Carbon Flux and Decoupling from Sulfate Reduction(Wiley-Blackwell, 2012) Wankel, Scott D.; Adams, Melissa Marie; Johnston, David; Hansel, Colleen; Joye, Samantha B.; Girguis, PeterThe anaerobic oxidation of methane (AOM) is a globally significant sink that regulates methane flux from sediments into the oceans and atmosphere. Here we examine mesophilic to thermophilic AOM in hydrothermal sediments recovered from the Middle Valley vent field, on the Juan de Fuca Ridge. Using continuous-flow sediment bioreactors and batch incubations, we characterized (i) the degree to which AOM contributes to net dissolved inorganic carbon flux, (ii) AOM and sulfate reduction (SR) rates as a function of temperature and (iii) the distribution and density of known anaerobic methanotrophs (ANMEs). In sediment bioreactors, inorganic carbon stable isotope mass balances results indicated that AOM accounted for between 16% and 86% of the inorganic carbon produced, underscoring the role of AOM in governing inorganic carbon flux from these sediments. At 90°C, AOM occurred in the absence of SR, demonstrating a striking decoupling of AOM from SR. An abundance of Fe(III)-bearing minerals resembling mixed valent Fe oxides, such as green rust, suggests the potential for a coupling of AOM to Fe(III) reduction in these metalliferous sediments. While SR bacteria were only observed in cooler temperature sediments, ANMEs allied to ANME-1 ribotypes, including a putative ANME-1c group, were found across all temperature regimes and represented a substantial proportion of the archaeal community. In concert, these results extend and reshape our understanding of the nature of high temperature methane biogeochemistry, providing insight into the physiology and ecology of thermophilic anaerobic methanotrophy and suggesting that AOM may play a central role in regulating biological dissolved inorganic carbon fluxes to the deep ocean from the organic-poor, metalliferous sediments of the global mid-ocean ridge hydrothermal vent system.Publication Geomicrobiological linkages between short-chain alkane consumption and sulfate reduction rates in seep sediments(Frontiers Media S.A., 2013) Bose, Arpita; Rogers, Daniel R.; Adams, Melissa Marie; Joye, Samantha B.; Girguis, PeterMarine hydrocarbon seeps are ecosystems that are rich in methane, and, in some cases, short-chain (C2–C5) and longer alkanes. C2–C4 alkanes such as ethane, propane, and butane can be significant components of seeping fluids. Some sulfate-reducing microbes oxidize short-chain alkanes anaerobically, and may play an important role in both the competition for sulfate and the local carbon budget. To better understand the anaerobic oxidation of short-chain n-alkanes coupled with sulfate-reduction, hydrocarbon-rich sediments from the Gulf of Mexico (GoM) were amended with artificial, sulfate-replete seawater and one of four n-alkanes (C1–C4) then incubated under strict anaerobic conditions. Measured rates of alkane oxidation and sulfate reduction closely follow stoichiometric predictions that assume the complete oxidation of alkanes to CO2 (though other sinks for alkane carbon likely exist). Changes in the δ13C of all the alkanes in the reactors show enrichment over the course of the incubation, with the C3 and C4 incubations showing the greatest enrichment (4.4 and 4.5‰, respectively). The concurrent depletion in the δ13C of dissolved inorganic carbon (DIC) implies a transfer of carbon from the alkane to the DIC pool (−3.5 and −6.7‰ for C3 and C4 incubations, respectively). Microbial community analyses reveal that certain members of the class Deltaproteobacteria are selectively enriched as the incubations degrade C1–C4 alkanes. Phylogenetic analyses indicate that distinct phylotypes are enriched in the ethane reactors, while phylotypes in the propane and butane reactors align with previously identified C3–C4 alkane-oxidizing sulfate-reducers. These data further constrain the potential influence of alkane oxidation on sulfate reduction rates (SRRs) in cold hydrocarbon-rich sediments, provide insight into their contribution to local carbon cycling, and illustrate the extent to which short-chain alkanes can serve as electron donors and govern microbial community composition and density.Publication The anaerobic oxidation of short-chain alkanes in hydrothermal vents(2014-06-06) Adams, Melissa Marie; Girguis, Peter R.; Cavanaugh, Colleen; Knoll, Andrew; Johnston, DavidMicroorganisms are central to the cycling of methane on Earth. The anaerobic oxidation of methane (AOM) is a globally important process in anoxic marine sediments, which is often coupled to the reduction of sulfate by anaerobic methanotroph (ANME) archaea and sulfate reducing bacteria (SRB). However, the environmental and geochemical conditions that constrain these microbial communities remain largely uncharacterized. In this dissertation, I present evidence that methane and C2-C4 alkanes are substantial sources of metabolic energy in sedimented hydrothermal vent systems. Furthermore, these studies demonstrate that AOM and C2-C4 alkane oxidation linked to sulfate reduction (SR) are governed by temperature and substrate availability.Publication Anaerobic Oxidation of Short-Chain Alkanes in Hydrothermal Sediments: Potential Influences on Sulfur Cycling and Microbial Diversity(Frontiers Research Foundation, 2013) Adams, Melissa Marie; Hoarfrost, Adrienne L.; Bose, Arpita; Joye, Samantha B.; Girguis, PeterShort-chain alkanes play a substantial role in carbon and sulfur cycling at hydrocarbon-rich environments globally, yet few studies have examined the metabolism of ethane \((C_2)\), propane \((C_3)\), and butane \((C_4)\) in anoxic sediments in contrast to methane \((C_1)\). In hydrothermal vent systems, short-chain alkanes are formed over relatively short geological time scales via thermogenic processes and often exist at high concentrations. The sediment-covered hydrothermal vent systems at Middle Valley (MV, Juan de Fuca Ridge) are an ideal site for investigating the anaerobic oxidation of \(C_1–C_4\) alkanes, given the elevated temperatures and dissolved hydrocarbon species characteristic of these metalliferous sediments. We examined whether MV microbial communities oxidized \(C_1–C_4\) alkanes under mesophilic to thermophilic sulfate-reducing conditions. Here we present data from discrete temperature (25, 55, and \(75^{\circ}C\)) anaerobic batch reactor incubations of MV sediments supplemented with individual alkanes. Co-registered alkane consumption and sulfate reduction (SR) measurements provide clear evidence for \(C_1–C_4\) alkane oxidation linked to SR over time and across temperatures. In these anaerobic batch reactor sediments, 16S ribosomal RNA pyrosequencing revealed that Deltaproteobacteria, particularly a novel sulfate-reducing lineage, were the likely phylotypes mediating the oxidation of \(C_2–C_4\) alkanes. Maximum \(C_1–C_4\) alkane oxidation rates occurred at \(55^{\circ}C\), which reflects the mid-core sediment temperature profile and corroborates previous studies of rate maxima for the anaerobic oxidation of methane (AOM). Of the alkanes investigated, \(C_3\) was oxidized at the highest rate over time, then \(C_4\), \(C_2\), and \(C_1\), respectively. The implications of these results are discussed with respect to the potential competition between the anaerobic oxidation of \(C_2–C_4\) alkanes with AOM for available oxidants and the influence on the fate of \(C_1\) derived from these hydrothermal systems.