@article {ISI:000373321200001,
	title = {{Nanocalorimetric Characterization of Microbial Activity in Deep Subsurface Oceanic Crustal Fluids}},
	journal = {FRONTIERS IN MICROBIOLOGY},
	volume = {7},
	year = {2016},
	month = {apr},
	type = {Article},
	abstract = {Although fluids within the upper oceanic basaltic crust harbor a substantial fraction of the total prokaryotic cells on Earth, the energy needs of this microbial population are unknown. In this study, a nanocalorimeter (sensitivity down to 1.2 nW ml(-1)) was used to measure the enthalpy of microbially catalyzed reactions as a function of temperature in samples from two distinct crustal fluid aquifers. Microorganisms in unamended, warm (63 degrees C) and geochemically altered anoxic fluids taken from 292 meters sub-basement (msb) near the Juan de Fuca Ridge produced 267.3 mJ of heat over the course of 97 h during a step-wise isothermal scan from 35.5 to 85.0 degrees C. Most of this heat signal likely stems from the germination of thermophilic endospores (6.66 x 10(4) cells ml(-1) FLUID) and their subsequent metabolic activity at temperatures greater than 50 degrees C. The average cellular energy consumption (5.68 pW cell(-1)) reveals the high metabolic potential of a dormant community transported by fluids circulating through the ocean crust. By contrast, samples taken from 293 msb from cooler (3.8 degrees C), relatively unaltered oxic fluids, produced 12.8 mJ of heat over the course of 14 h as temperature ramped from 34.8 to 43.0 degrees C. Corresponding cell-specific energy turnover rates (0.18 pW cell(-1)) were converted to oxygen uptake rates of 24.5 nmol O-2 ml(-1) FLUID d(-1), validating previous model predictions of microbial activity in this environment. Given that the investigated fluids are characteristic of expansive areas of the upper oceanic crust, the measured metabolic heat rates can be used to constrain boundaries of habitability and microbial activity in the oceanic crust.},
	keywords = {ROV Jason (Remotely Operated Vehicle)},
	issn = {1664-302X},
	doi = {10.3389/fmicb.2016.00454},
	author = {Robador, Alberto and LaRowe, Douglas E and Jungbluth, Sean P and Lin, Huei-Ting and Rappe, Michael S and Nealson, Kenneth H and Amend, Jan P}
}
@article {ISI:000371481100019,
	title = {{Thermal and geochemical influences on microbial biogeography in the hydrothermal sediments of Guaymas Basin, Gulf of California}},
	journal = {ENVIRONMENTAL MICROBIOLOGY REPORTS},
	volume = {8},
	number = {1},
	year = {2016},
	month = {feb},
	pages = {150{\textendash}161},
	type = {Article},
	abstract = {Extreme thermal gradients and compressed metabolic zones limit the depth range of microbial colonization in hydrothermally active sediments at Guaymas Basin. We investigated the physicochemical characteristics of this ecosystem and their influence on microbial community structure. Temperature-related trends of C-13 values of methane and dissolved inorganic carbon from 36 sediment cores suggest in situ thermal limits for microbial anaerobic methane oxidation and organic carbon re-mineralization near 80 degrees C and 100 degrees C respectively. Temperature logging probes deposited in hydrothermal sediments for 8 days demonstrate substantial thermal fluctuations of up to 25 degrees C. Putative anaerobic methanotroph (ANME) populations dominate the archaeal community, transitioning from ANME-1 archaea in warm surficial sediments towards ANME-1 Guaymas archaea as temperatures increase downcore. Since ANME archaea performing anaerobic oxidation of methane double on longer time scales (months) compared with relatively rapid in situ temperature fluctuations (hours to days), we conclude that ANME archaea possess a high tolerance for short-term shifts in the thermal regime.},
	keywords = {HOV Alvin (Human Occupied Vehicle)},
	issn = {1758-2229},
	doi = {10.1111/1758-2229.12365},
	author = {McKay, Luke and Klokman, Vincent W and Mendlovitz, Howard P and LaRowe, Douglas E and Hoer, Daniel R and Albert, Daniel and Amend, Jan P and Teske, Andreas}
}
@article {ISI:000348807500001,
	title = {{Activity and phylogenetic diversity of sulfate-reducing microorganisms in low-temperature subsurface fluids within the upper oceanic crust}},
	journal = {FRONTIERS IN MICROBIOLOGY},
	volume = {5},
	year = {2015},
	month = {jan},
	type = {Article},
	abstract = {The basaltic ocean crust is the largest aquifer system on Earth, yet the rates of biological activity in this environment are unknown. Low-temperature ({\textless}100 degrees C) fluid samples were investigated from two borehole observatories in the Juan de Fuca Ridge (JFR) flank, representing a range of upper oceanic basement thermal and geochemical properties. Microbial sulfate reduction rates (SRR) were measured in laboratory incubations with S-35-sulfate over a range of temperatures and the identity of the corresponding sulfate-reducing microorganisms (SRM) was studied by analyzing the sequence diversity of the functional marker dissimilatory (bi)sulfite reductase (dsrAB) gene. We found that microbial sulfate reduction was limited by the decreasing availability of organic electron donors in higher temperature, more altered fluids. Thermodynamic calculations indicate energetic constraints for metabolism, which together with relatively higher cell-specific SRR reveal increased maintenance requirements, consistent with novel species-level dsrAB phylotypes of thermophilic SRM. Our estimates suggest that microbially-mediated sulfate reduction may account for the removal of organic matter in fluids within the upper oceanic crust and underscore the potential quantitative impact of microbial processes in deep subsurface marine crustal fluids on marine and global biogeochemical carbon cycling.},
	keywords = {ROV Jason (Remotely Operated Vehicle)},
	issn = {1664-302X},
	doi = {10.3389/fmicb.2014.00748},
	author = {Robador, Alberto and Jungbluth, Sean P and LaRowe, Douglas E and Bowers, Robert M and Rappe, Michael S and Amend, Jan P and Cowen, James P}
}
