Publications

2014
Beinart RA, Nyholm SV, Dubilier N, Girguis PR. Intracellular Oceanospirillales inhabit the gills of the hydrothermal vent snail Alviniconcha with chemosynthetic, gamma-Proteobacterial symbionts. Environmental Microbiology Reports. 2014;6 :656-664.Abstract

Associations between bacteria from the -Proteobacterial order Oceanospirillales and marine invertebrates are quite common. Members of the Oceanospirillales exhibit a diversity of interactions with their various hosts, ranging from the catabolism of complex compounds that benefit host growth to attacking and bursting host nuclei. Here, we describe the association between a novel Oceanospirillales phylotype and the hydrothermal vent snail Alviniconcha. Alviniconcha typically harbour chemoautotrophic - or epsilon-Proteobacterial symbionts inside their gill cells. Via fluorescence in situ hybridization and transmission electron microscopy, we observed an Oceanospirillales phylotype (named AOP for AlviniconchaOceanospirillales phylotype') in membrane-bound vacuoles that were separate from the known - or epsilon-Proteobacterial symbionts. Using quantitative polymerase chain reaction, we surveyed 181 Alviniconcha hosting -Proteobacterial symbionts and 102 hosting epsilon-Proteobacterial symbionts, and found that the population size of AOP was always minor relative to the canonical symbionts (median 0.53% of the total quantified 16S rRNA genes). Additionally, we detected AOP more frequently in Alviniconcha hosting -Proteobacterial symbionts than in those hosting epsilon-Proteobacterial symbionts (96% and 5% of individuals respectively). The high incidence of AOP in -Proteobacteria hosting Alviniconcha implies that it could play a significant ecological role either as a host parasite or as an additional symbiont with unknown physiological capacities.

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Sperling EA, Frieder CA, Raman AV, Girguis PR, Levin LA, Knoll AH. Oxygen, ecology, and the Cambrian radiation of animals. Integrative and Comparative Biology. 2014;54 :E198-E198.
2013
Girguis PR, DeCharon A, Herren CM. Capitalizing on Expertise in Marine Education and Outreach to Broaden Impacts. The Journal of Marine Education. 2013;28 (3) :39-40. (pdf)
Girguis PR, Choffnes ER, LeighAnne O, Wizemann TM. The Science and Applications of Microbial Genomics. 2013.
Adams MM, Hoarfrost AL, Bose A, Joye SB, Girguis PR. Anaerobic oxidation of short-chain alkanes in hydrothermal sediments: potential influences on sulfur cycling and microbial diversity. Frontiers in Microbiology. 2013;4 :1-11.Abstract

Short-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 degrees 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 degrees 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.

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Olins HC, Rogers DR, Frank KL, Vidoudez C, Girguis PR. Assessing the influence of physical, geochemical and biological factors on anaerobic microbial primary productivity within hydrothermal vent chimneys. Geobiology. 2013;11 :279-293.Abstract

Chemosynthetic primary production supports hydrothermal vent ecosystems, but the extent of that productivity and its governing factors have not been well constrained. To better understand anaerobic primary production within massive vent deposits, we conducted a series of incubations at 4, 25, 50 and 90 degrees C using aggregates recovered from hydrothermal vent structures. We documented in situ geochemistry, measured autochthonous organic carbon stable isotope ratios and assessed microbial community composition and functional gene abundances in three hydrothermal vent chimney structures from Middle Valley on the Juan de Fuca Ridge. Carbon fixation rates were greatest at lower temperatures and were comparable among chimneys. Stable isotope ratios of autochthonous organic carbon were consistent with the CalvinBensonBassham cycle being the predominant mode of carbon fixation for all three chimneys. Chimneys exhibited marked differences in vent fluid geochemistry and microbial community composition, with structures being differentially dominated by gamma () or epsilon (epsilon) proteobacteria. Similarly, qPCR analyses of functional genes representing different carbon fixation pathways showed striking differences in gene abundance among chimney structures. Carbon fixation rates showed no obvious correlation with observed in situ vent fluid geochemistry, community composition or functional gene abundance. Together, these data reveal that (i) net anaerobic carbon fixation rates among these chimneys are elevated at lower temperatures, (ii) clear differences in community composition and gene abundance exist among chimney structures, and (iii) tremendous spatial heterogeneity within these environments likely confounds efforts to relate the observed rates to in situ microbial and geochemical factors. We also posit that microbes typically thought to be mesophiles are likely active and growing at cooler temperatures, and that their activity at these temperatures comprises the majority of endolithic anaerobic primary production in hydrothermal vent chimneys.

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Ussler W, Preston C, Tavormina P, Pargett D, Jensen S, Roman B, Marin R, Shah SR, Girguis PR, Birch JM, et al. Autonomous Application of Quantitative PCR in the Deep Sea: In Situ Surveys of Aerobic Methanotrophs Using the Deep-Sea Environmental Sample Processor. Environmental Science & Technology. 2013;47 :9339-9346.Abstract

Recent advances in ocean observing systems and genomic technologies have led to the development of the deep-sea environmental sample processor (D-ESP). The DESP filters particulates from seawater at depths up to 4000 m and applies a variety of molecular assays to the particulates, including quantitative PCR (qPCR), to identify particular organisms and genes in situ. Preserved samples enable laboratory-based validation of in situ results and expanded studies of genomic diversity and gene expression. Tests of the D-ESP at a methane-rich mound in the Santa Monica Basin centered on detection of 16S rRNA and particulate methane monooxygenase (pmoA) genes for two putative aerobic methanotrophs. Comparison of in situ qPCR results with laboratory-based assays of preserved samples demonstrates the D-ESP generated high-quality qPCR data while operating autonomously on the seafloor. Levels of 16S rRNA and pmoA cDNA detected in preserved samples are consistent with an active community of aerobic methanotrophs near the methane-rich mound. These findings are substantiated at low methane sites off Point Conception and in Monterey Bay where target genes are at or below detection limits. Successful deployment of the D-ESP is a major step toward developing autonomous systems to facilitate a wide range of marine microbiological investigations.

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Robidart J, Callister SJ, Song PF, Nicora CD, Wheat CG, Girguis PR. Characterizing Microbial Community and Geochemical Dynamics at Hydrothermal Vents Using Osmotically Driven Continuous Fluid Samplers. Environmental Science & Technology. 2013;47 :4399-4407.Abstract

Microbes play a key role in mediating aquatic biogeochemical cycles. However, our understanding of the relationships between microbial phylogenetic/physiological diversity and habitat physicochemical characteristics is restrained by our limited capacity to concurrently collect microbial and geochemical samples at appropriate spatial and temporal scales. Accordingly, we have developed a low-cost, continuous fluid sampling system (the Biological OsmoSampling System, or BOSS) to address this limitation. The BOSS does not use electricity, can be deployed in harsh/remote environments, and collects/preserves samples with daily resolution for >1 year. Here, we present data on the efficacy of DNA and protein preservation during a 1.5 year laboratory study as well as the results of two field deployments at deep-sea hydrothermal vents, wherein we examined changes in microbial diversity, protein expression, and geochemistry over time. Our data reveal marked changes in microbial composition co-occurring with changes in hydrothermal fluid composition as well as the temporal dynamics of an enigmatic sulfide-oxidizing symbiont in its free-living state. We also present the first data on in situ protein preservation and expression dynamics highlighting the BOSS's potential utility in meta-proteomic studies. These data illustrate the value of using BOSS to study relationships among microbial and geochemical phenomena and environmental conditions.

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Frank KL, Rogers DR, Olins HC, Vidoudez C, Girguis PR. Characterizing the distribution and rates of microbial sulfate reduction at Middle Valley hydrothermal vents. ISME Journal. 2013;7 :1391-1401.Abstract

Few studies have directly measured sulfate reduction at hydrothermal vents, and relatively little is known about how environmental or ecological factors influence rates of sulfate reduction in vent environments. A better understanding of microbially mediated sulfate reduction in hydrothermal vent ecosystems may be achieved by integrating ecological and geochemical data with metabolic rate measurements. Here we present rates of microbially mediated sulfate reduction from three distinct hydrothermal vents in the Middle Valley vent field along the Juan de Fuca Ridge, as well as assessments of bacterial and archaeal diversity, estimates of total biomass and the abundance of functional genes related to sulfate reduction, and in situ geochemistry. Maximum rates of sulfate reduction occurred at 90 degrees C in all three deposits. Pyrosequencing and functional gene abundance data revealed differences in both biomass and community composition among sites, including differences in the abundance of known sulfate-reducing bacteria. The abundance of sequences for Thermodesulfovibro-like organisms and higher sulfate reduction rates at elevated temperatures suggests that Thermodesulfovibro-like organisms may have a role in sulfate reduction in warmer environments. The rates of sulfate reduction presented here suggest that-within anaerobic niches of hydrothermal deposits-heterotrophic sulfate reduction may be quite common and might contribute substantially to secondary productivity, underscoring the potential role of this process in both sulfur and carbon cycling at vents.

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Wankel SD, Huang YW, Gupta M, Provencal R, Leen JB, Fahrland A, Vidoudez C, Girguis PR. Characterizing the Distribution of Methane Sources and Cycling in the Deep Sea via in Situ Stable Isotope Analysis. Environmental Science & Technology. 2013;47 :1478-1486.Abstract

The capacity to make in situ geo-referenced measurements of methane concentration and stable isotopic composition (delta C-13(CH4)) would greatly improve our understanding of the distribution and type of methane sources in the environment, allow refined determination of the extent to which microbial production and consumption contributes to methane cycling, and enable the testing of hypotheses about the sensitivity of methane cycling to changes in environmental conditions. In particular, characterizing biogeochemical methane cycling dynamics in the deep ocean is hampered by a number of challenges, especially in environments where high methane concentrations preclude intact recovery of undisturbed samples. To that end, we have developed an in situ analyzer capable of delta C-13(CH4) measurements in the deep ocean. Here we present data from laboratory and field studies in which we characterize the instrument's analytical capabilities and performance and provide the first in situ stable isotope based characterization of the influence of anaerobic methane oxidation on methane flux from seep sediments. These data illustrate how in situ measurements can permit finer-scale analyses of variations in AOM activity, and facilitate advances in using delta C-13(CH4) and other isotopic systems to interrogate biogeochemical cycles in the deep sea and other remote or challenging environments.

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Pargett DM, Jensen SD, Roman BA, Preston CM, Ussler W, Girguis PR, Marin R, Birch JM, Scholin CA. Deep Water Instrument for Microbial Identification, Quantification, and Archiving. 2013 Oceans - San Diego. 2013.Abstract

A deep ocean robotic platform capable of in situ microbial identification and quantification at depths to 4000 m has been developed. The platform is a free benthic lander, containing a low pressure microbial instrument and deep ocean sampling systems that can monitor and collect raw seawater from multiple sources, then decompress the raw seawater for processing by the detection instrument. This has enabled the autonomous collection, processing, and archiving of microbes from multiple sites. This allows for direct, time correlated comparison of different microbial populations along with the seawater physical and chemical composition.

Bose A, Rogers DR, Adams MM, Joye SB, Girguis PR. Geomicrobiological linkages between short-chain alkane consumption and sulfate reduction rates in seep sediments. Frontiers in Microbiology. 2013;4.Abstract

Marine hydrocarbon seeps are ecosystems that are rich in methane, and, in some cases, short-chain (C-2-C-5) and longer alkanes. C-2-C-4 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 (C-1-C-4) 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 delta C-13 of all the alkanes in the reactors show enrichment over the course of the incubation, with the C-3 and C-4 incubations showing the greatest enrichment (4.4 and 4.5 parts per thousand, respectively). The concurrent depletion in the delta C-13 of dissolved inorganic carbon (DIC) implies a transfer of carbon from the alkane to the DIC pool (-3.5 and -6.7 parts per thousand for C-3 and C-4 incubations, respectively). Microbial community analyses reveal that certain members of the class Deltaproteobacteria are selectively enriched as the incubations degrade C-1-C-4 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 C-3-C-4 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.

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Sylvan JB, Sia TY, Haddad AG, Briscoe LJ, Toner BM, Girguis PR, Edwards KJ. Low temperature geomicrobiology follows host rock composition along a geochemical gradient in Lau Basin. Frontiers in Microbiology. 2013;4.Abstract

The East Lau Spreading Center (ELSC) and Valu Fa Ridge (VFR) comprise a ridge segment in the southwest Pacific Ocean where rapid transitions in the underlying mantle chemistry manifest themselves as gradients in seafloor rock geochemistry. We studied the geology and microbial diversity of three silicate rock samples and three inactive sulfide chimney samples collected, from north to south, at the vent fields Kilo Moana, ABE, Tui Malila, and Mariner. This is the first study of microbial populations on basaltic andesite, which was sampled at Mariner vent field. Silicate rock geochemistry exhibits clear latitudinal trends that are mirrored by changes in bacterial community composition. alpha-proteobacteria, epsilon-proteobacteria, and Bacteroidetes are most common on a silicate collected from Kilo Moana and their proportions decrease linearly on silicates collected further south. Conversely, a silicate from Mariner vent field hosts high proportions of a unique lineage of Chloroflexi unrelated (<90% sequence similarity) to previously recovered environmental clones or isolates, which decrease at ABE and are absent at Kilo Moana. The exteriors of inactive sulfide structures are dominated by lineages of sulfur oxidizing alpha-proteobacteria, gamma-proteobacteria, and epsilon-proteobacteria, while the interior of one chimney is dominated by putative sulfur-reducing delta-proteobacteria. A comparison of bacterial communities on inactive sulfides from this and previous studies reveals the presence of a clade of uncultured Bacteroidetes exclusive to sulfidic environments, and a high degree of heterogeneity in bacterial community composition from one sulfide structure to another. In light of the heterogeneous nature of bacterial communities observed here and in previous studies of both active and inactive hydrothermal sulfide structures, the presence of numerous niches may be detected on these structures in the future by finer scale sampling and analysis.

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Sanders JG, Beinart RA, Stewart FJ, Delong EF, Girguis PR. Metatranscriptomics reveal differences in in situ energy and nitrogen metabolism among hydrothermal vent snail symbionts. ISME Journal. 2013;7 :1556-1567.Abstract

Despite the ubiquity of chemoautotrophic symbioses at hydrothermal vents, our understanding of the influence of environmental chemistry on symbiont metabolism is limited. Transcriptomic analyses are useful for linking physiological poise to environmental conditions, but recovering samples from the deep sea is challenging, as the long recovery times can change expression profiles before preservation. Here, we present a novel, in situ RNA sampling and preservation device, which we used to compare the symbiont metatranscriptomes associated with Alviniconcha, a genus of vent snail, in which specific host-symbiont combinations are predictably distributed across a regional geochemical gradient. Metatranscriptomes of these symbionts reveal key differences in energy and nitrogen metabolism relating to both environmental chemistry (that is, the relative expression of genes) and symbiont phylogeny (that is, the specific pathways employed). Unexpectedly, dramatic differences in expression of transposases and flagellar genes suggest that different symbiont types may also have distinct life histories. These data further our understanding of these symbionts' metabolic capabilities and their expression in situ, and suggest an important role for symbionts in mediating their hosts' interaction with regional-scale differences in geochemistry.

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Sperling EA, Frieder CA, Raman AV, Girguis PR, Levin LA, Knoll AH. Oxygen, ecology, and the Cambrian radiation of animals. Proceedings of the National Academy of Sciences of the United States of America. 2013;110 (33) :13446-13451.Abstract

The Proterozoic-Cambrian transition records the appearance of essentially all animal body plans (phyla), yet to date no single hypothesis adequately explains both the timing of the event and the evident increase in diversity and disparity. Ecological triggers focused on escalatory predator-prey "arms races" can explain the evolutionary pattern but not its timing, whereas environmental triggers, particularly ocean/atmosphere oxygenation, do the reverse. Using modern oxygen minimum zones as an analog for Proterozoic oceans, we explore the effect of low oxygen levels on the feeding ecology of polychaetes, the dominant macrofaunal animals in deep-sea sediments. Here we show that low oxygen is clearly linked to low proportions of carnivores in a community and low diversity of carnivorous taxa, whereas higher oxygen levels support more complex food webs. The recognition of a physiological control on carnivory therefore links environmental triggers and ecological drivers, providing an integrated explanation for both the pattern and timing of Cambrian animal radiation.

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Reimers CE, Alleau Y, Bauer JE, Delaney J, Girguis PR, Schrader PS, Stecher HA. Redox effects on the microbial degradation of refractory organic matter in marine sediments. Geochimica Et Cosmochimica Acta. 2013;121 :582-598.Abstract

Microbially mediated reduction-oxidation (redox) reactions are often invoked as being the mechanisms by which redox state influences the degradation of sedimentary organic matter (OM) in the marine environment. To evaluate the effects of elevated, oscillating and reduced redox potentials on the fate of primarily aged, mineral-adsorbed OM contained in continental shelf sediments, we used microbial fuel cells to control redox state within and around marine sediments, without amending the sediments with reducing or oxidizing substances. We subsequently followed electron fluxes in the redox elevated and redox oscillating treatments, and related sediment chemical, isotopic and bacterial community changes to redox conditions over a 748-day experimental period.The electron fluxes of the elevated and oscillating redox cells were consistent with models of organic carbon (OC) oxidation with time-dependent first-order rate constants declining from 0.023 to 0.005 y(-1), in agreement with rate constants derived from typical OC profiles and down core ages of offshore sediments, or from sulfate reduction rate measurements in similar sediments. Moreover, although cumulative electron fluxes were higher in the continuously elevated redox treatment, incremental rates of electron harvesting in the two treatments converged over the 2 year experiment. These similar rates were reflected in chemical indicators of OM metabolism such as dissolved OC and ammonia, and particulate OC concentrations, which were not significantly different among all treatments and controls over the experimental time-scale. In contrast, products of carbonate and opal dissolution and metal mobilization showed greater enrichments in sediments with elevated and oscillating redox states.Microbial community composition in anode biofilms and surrounding sediments was assessed via high-throughput 16S rRNA gene sequencing, and these analyses revealed that the elevated and oscillatory redox treatments led to the enrichment of Deltaproteobacteria on the sediment-hosted anodes over time. Many Deltaproteobacteria are capable of using electrodes as terminal electron acceptors to completely oxidize organic substrates. Notably, Deltaproteobacteria were not measurably enriched in the sediments adjacent to anodes, suggesting that - in these experiments - electron-shuttling bacterial networks did not radiate out away from the electrodes, affecting millimeters or centimeters of sediment. Rather, microbial phylotypes allied to the Clostridia appeared to dominate in the sediment amongst all treatments, and likely played essential roles in converting complex dissolved and particulate sources of OM to simple fermentation products. Thus, we advance that the rate at which fermentation products are generated and migrate to oxidation fronts is what limits the remineralization of OM in many subsurface sediments removed from molecular oxygen. This is a diagenetic scenario that is consistent with the discharging behavior of redox oscillating sediment MFCs. It is also compatible with hypotheses that molecular O-2 - and not just the resulting elevated redox potential - may be required to effectively catalyze the degradation of refractory OM. Such decomposition reactions have been suggested to depend on substrate interactions with highly reactive oxygen- containing radicals and/or with specialized extracellular enzymes produced by aerobic prokaryotic or eukaryotic cells. (c) 2013 Elsevier Ltd. All rights reserved.

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Kolodkin-Gal I, Elsholz AKW, Muth C, Girguis PR, Kolter R, Losick R. Respiration control of multicellularity in Bacillus subtilis by a complex of the cytochrome chain with a membrane-embedded histidine kinase. Genes & Development. 2013;27 :887-899.Abstract

Bacillus subtilis forms organized multicellular communities known as biofilms wherein the individual cells are held together by a self-produced extracellular matrix. The environmental signals that promote matrix synthesis remain largely unknown. We discovered that one such signal is impaired respiration. Specifically, high oxygen levels suppressed synthesis of the extracellular matrix. In contrast, low oxygen levels, in the absence of an alternative electron acceptor, led to increased matrix production. The response to impaired respiration was blocked in a mutant lacking cytochromes caa(3) and bc and markedly reduced in a mutant lacking kinase KinB. Mass spectrometry of proteins associated with KinB showed that the kinase was in a complex with multiple components of the aerobic respiratory chain. We propose that KinB is activated via a redox switch involving interaction of its second transmembrane segment with one or more cytochromes under conditions of reduced electron transport. In addition, a second kinase (KinA) contributes to the response to impaired respiration. Evidence suggests that KinA is activated by a decrease in the nicotinamide adenine dinucleotide (NAD(+))/NADH ratio via binding of NAD(+) to the kinase in a PAS domain A-dependent manner. Thus, B. subtilis switches from a unicellular to a multicellular state by two pathways that independently respond to conditions of impaired respiration.

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Schrader PS, Doolan C, Reimers CE, Girguis PR, Wolf M, Green D. Sensors and Acoustic Modems Powered by Benthic Microbial Fuel Cells at the MARS Observatory. 2013 Oceans - San Diego. 2013.Abstract

The goals of this project were three-fold: 1) to power underwater instruments with energy harvested from deep sea, organic poor sediments using Benthic Microbial Fuel Cells (BMFCs); 2) to relay instrument data acoustically -and in near-real time-through a cabled seafloor observatory or surface vessel, as appropriate; and 3) to characterize the operational performance of these interactive systems during in situ deployments. Two BMFC-underwater sensing/communications packages were demonstrated near the Monterey Accelerated Research System (MARS) observatory in Monterey Bay, California. MARS is a cabled observatory that resides in deep water (similar to 890 m), about 37 km (23 miles) seaward of the Monterey Bay Aquarium Research Institute (MBARI).The BMFCs were constructed using a cylindrical chamber design with a 0.28 m(2) footprint. Each BMFC was used to power an Aanderaa dissolved O-2/temperature or conductivity/temperature sensor, as well as a Teledyne Benthos compact acoustic modem which contained an integrated power management platform (PMP) for the complete system. The packages were deployed from a surface vessel and allowed to descend freely to the seafloor, at locations approximately 0.5 km away from the MARS node, at depths of 863 and 895 m. The PMPs were programmed to record data from both the sensors and the BMFC (whole cell voltage, capacitor voltage, and battery voltage) on an hourly basis, and to monitor overall microbial fuel cell energy production on a daily basis. Post-deployment, BMFC 1 generated a net surplus of energy from days 98 through 166, and remained operational for 210 days. BMFC 2 began generating a surplus of energy on day 54 and remained operational for 158 days. Data recovered from the oceanographic sensors was transmitted acoustically over both the MARS node and to a research vessel, underscoring the utility of this technology.

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2012
Wankel SD, Adams MM, Johnston DT, Hansel CM, Joye SB, Girguis PR. Anaerobic methane oxidation in metalliferous hydrothermal sediments: influence on carbon flux and decoupling from sulfate reduction. Environmental Microbiology . 2012;14 :2726-2740.Abstract

The 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 degrees 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.

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Gardel EJ, Nielsen ME, Grisdela PT, Girguis PR. Duty Cycling Influences Current Generation in Multi-Anode Environmental Microbial Fuel Cells. Environmental Science & Technology. 2012;46 :5222-5229.Abstract

Improving microbial fuel cell (MFC) performance continues to be the subject of research, yet the role of operating conditions, specifically duty cycling, on MFC performance has been modestly addressed. We present a series of studies in which we use a 15-anode environmental MFC to explore how duty cycling (variations in the time an anode is connected) influences cumulative charge, current, and microbial composition. The data reveal particular switching intervals that result in the greatest time-normalized current. When disconnection times are sufficiently short, there is a striking decrease in current due to an increase in the overall electrode reaction resistance. This was observed over a number of whole cell potentials. Based on these results, we posit that replenishment of depleted electron donors within the biofilm and surrounding diffusion layer is necessary for maximum charge transfer, and that proton flux may be not limiting in the highly buffered aqueous phases that are common among environmental MFCs. Surprisingly, microbial diversity analyses found no discernible difference in gross community composition among duty cycling treatments, suggesting that duty cycling itself has little or no effect. Such duty cycling experiments are valuable in determining which factors govern performance of bioelectrochemical systems and might also be used to optimize field-deployed systems.

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