@article {ISI:000345292900023,
	title = {{Diversity and abundance of Bacteria and nirS-encoding denitrifiers associated with the Juan de Fuca Ridge hydrothermal system}},
	journal = {ANNALS OF MICROBIOLOGY},
	volume = {64},
	number = {4},
	year = {2014},
	month = {dec},
	pages = {1691{\textendash}1705},
	type = {Article},
	abstract = {Denitrification, which results in the loss of bioavailable nitrogen-an essential macronutrient for all living organisms-may potentially affect chemosynthetic primary production in hydrothermal vent ecosystems where sub-oxic conditions favorable to denitrification are common. Here we describe the diversity and abundance of denitrifying bacteria in the subsurface biosphere at Axial Volcano and the Endeavour Segment on the Juan de Fuca Ridge using a combination of quantitative polymerase chain reaction assays, and small subunit ribosomal RNA (SSU or 16S rRNA) pyrotag and nitrite reductase (nirS) clone library sequencing methods. Bacterial communities were diverse and dominated by members of the epsilon- and gamma-proteobacteria, including taxonomic groups containing known denitrifiers. Assemblages of denitrifiers that could be evaluated by nirS gene sequence comparisons showed low diversity. The single nirS sequence shared by the two locations, affiliated with a gamma-proteobacteria isolated from estuarine sediments (Pseudomonas sp. BA2), represented more than half of all sequences recovered when clustered at 97 {\%} identity. All other nirS sequences clustered into different taxonomic groups, indicating important differences in denitrifier community membership between the two sites. Total nirS gene abundance was at least two orders of magnitude lower than 16S rRNA abundance. Overall, our results demonstrate that the diversity and abundance of the nirS gene-containing bacterial community are rather low, as might be expected under the extreme conditions encountered in the subsurface biosphere of hydrothermal vent systems, and do not correlate clearly with any environmental variables investigated (i.e., pH, temperature, and H2S, NO3-, NH4+ concentrations).},
	keywords = {HOV Alvin (Human Occupied Vehicle), ROV Jason (Remotely Operated Vehicle)},
	issn = {1590-4261},
	doi = {10.1007/s13213-014-0813-3},
	author = {Bourbonnais, Annie and Juniper, S Kim and Butterfield, David A and Anderson, Rika E and Lehmann, Moritz F}
}
@article {ISI:000299990700001,
	title = {{Subseafloor nitrogen transformations in diffuse hydrothermal vent fluids of the Juan de Fuca Ridge evidenced by the isotopic composition of nitrate and ammonium}},
	journal = {GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS},
	volume = {13},
	year = {2012},
	month = {feb},
	type = {Article},
	abstract = {Little is known about dissolved inorganic nitrogen (DIN) transformations in hydrothermal vent (HV) fluids. Here, we present the first isotopic measurements of nitrate (delta N-15 and delta O-18) and ammonium (delta N-15) from three HV fields on the Juan de Fuca ridge (NE-Pacific). The dominant process that drives DIN concentration variations in low-T diffuse fluids is water mass mixing below the seafloor, with no effect on the DIN isotope ratios. Strong inter-site variations in the concentration and delta N-15 of NH4+ in high-T fluids suggest different subsurface nitrogen (N) sources (deep-sea nitrate versus organic sediments) for hydrothermally discharged ammonium. Low NH4+ community N isotope effects ({\textless}3 parts per thousand) for net NH4+ consumption suggest an important contribution from gross ammonium regeneration in low-T fluids. Elevation of HV nitrate N-15/N-14 and O-18/O-16 over deep-sea mean isotope values at some sites, concomitant with decreased nitrate concentrations, indicate assimilatory or dissimilatory nitrate consumption by bacteria in the subsurface, with relatively low community N isotope effects ((15)epsilon(k) {\textless} 3 parts per thousand). The low N isotope effects suggest that nitrate assimilation or denitrification occur in bacterial mats, and/or in situ production of low delta N-15 nitrate. A significantly stronger relative increase for nitrate delta O-18 than for delta N-15 was observed at many sites, resulting in marked deviations from the 1:1 relationship for nitrate delta N-15 versus delta O-18 that is expected for nitrate reduction in marine settings. Simple box-model calculation show that the observed un-coupling of N and O nitrate isotope ratios is consistent with nitrate regeneration by either nitrite reoxidation and/or partial nitrification of hydrothermal ammonium (possibly originating from N-2 fixation). Our isotope data confirm the role of subsurface microbial communities in modulating hydrothermal fluxes to the deep ocean.},
	keywords = {HOV Alvin (Human Occupied Vehicle), ROV Jason (Remotely Operated Vehicle)},
	issn = {1525-2027},
	doi = {10.1029/2011GC003863},
	author = {Bourbonnais, Annie and Lehmann, Moritz F and Butterfield, David A and Juniper, S Kim}
}
