The radioactivity of the Zn35S and the remaining sulfate from the supernatant (35SO42-) were measured via liquid scintillation counter in Ultima Gold scintillation cocktail (ThermoFisher Inc., Waltham, MA).
|Created||November 13, 2015|
|Modified||August 19, 2016|
|State||Final no updates expected|
Maximum rates of microbially mediated sulfate reduction from three hydrothermal vents along the Juan de Fuca Ridge.
Sampling and Analytical Methodology: Once on board ship, samples were directly transferred to sterile anaerobic
seawater and handled/processed using appropriate sterile microbiological techniques. Subsamples were immediately transferred to gastight jars (Freund Container Inc.), filled with sterile anaerobic seawater containing 2 mM sodium sulfide at pH 6, and stored at 4 degrees C. Upon return to the laboratory, all samples were maintained in anaerobic seawater
(0.2 um filter-sterilized prior to use) supplemented with 2mM ΣH2S (defined as the sum of H2S, HS- and S2-) and adjusted to pH 6. The vent-like media was replenished every 8 to 12 weeks, and all samples were kept in the dark and 4 degrees C prior to incubation. Hydrothermal deposits were homogenized in a commercial blender (Xtreme™
blender, Waring Inc.) under a nitrogen atmosphere. Anaerobic homogenization was designed to minimize fine-scale geochemical and microbial heterogeneity and facilitate more accurate experimental replication. Hydrothermal homogenate (made up of both mineral deposit and interstitial fluid)) was aliquoted volumetrically (7.5 mL, ca. 29 g wet weight and ca. 20 g dry weight) into Balch tubes in an anaerobic chamber. The tubes were supplemented with 15 mL of sterile artificial vent fluid media designed to mimic the geochemical composition of fluids within the pores of a sulfide deposit (pH 6, 14 mM SO42-, 2.3 mM NaHCO3, 1 mM H2S, and 10 uM each of pyruvate, citrate, formate, acetate, lactate). Organic acid concentrations are comparable to those measured in situ along the Juan de Fuca ridge (Lang et al. 2006). Sufficient 35SO42- was added to achieve 555 kBq (15 uCi) of activity. Due to technical difficulties with post processing methodology, shipboard incubations using fresh material were not successful. The data presented here were generated using samples that had been maintained in sulfidic ventlike effluent (as described above) for one year. Samples were incubated anaerobically for 7 days at 4, 30, 40, 50, 60, 80 and 90 degrees C. Controls for sulfate reduction consisted of samples amended with 28 mM molybdate, a competitive inhibitor of sulfate reduction (Saleh et al. 1964; Newport & Nedwell, 1988). Six biological replicates were run for each treatment, and three biological replicates for each control. Upon completion, reactions were quenched with the injection of 5 mL 25% zinc acetate (which is ~20-fold more Zinc than the maximum sulfide concentration), and all samples were frozen at -20 degrees C to enable further analysis.
1 gram (wet weight) of crushed mineral (about 60% mineral, 30% interstitial fluid) was added to 10 mL of a 1:1 ethanol to water solution in the chromium distillation apparatus, and then degassed with nitrogen for 15 minutes to achieve anaerobicity. 8 mL of 12 N HCl and 16 mL of 1 M reduced chromium chloride was added anaerobically to the chamber and gently heated to a slow boil for 3 hours to evolve hydrogen sulfide gas. The resulting sulfide gas was carried via nitrogen gas through a condenser to remove any ethanol or water vapor, and was then trapped as zinc sulfide in a 25% zinc acetate solution. The radioactivity of the resulting sulfide (Zn35S) and the remaining sulfate from the supernatant (35SO42-) were measured via liquid scintillation counter in Ultima Gold scintillation cocktail (ThermoFisher Inc., Waltham, MA).
Data Processing: Sulfate reduction rates (SRR) were calculated as in (Fossing & Jorgensen, 1989) using the following calculation:
SRR = (nSO42- * a * 1.06) / ((a + A) * t)
Where nSO42- is the quantity (in moles) of sulfate added to each incubation (14 mM * 15 mL = 210 umol), a is the activity (dpm) of the trapped sulfide, 1.06 is the fractionation factor between the sulfide and sulfate pools, A is the activity of the sulfate pool at the completion of the incubation and t is the incubation time (days). The rates are presented in units of nmol S g-1 day-1.
unique sample identification or number; any combination of alpha numeric characters; precise definition is file dependent
latitude, in decimal degrees, North is positive, negative denotes South; Reported in some datasets as degrees, minutes
longitude, in decimal degrees, East is positive, negative denotes West; Reported in some datsets as degrees, minutes
Depth from which sample was obtained.
Observation/sample depth below the sea surface. Units often reported as: meters, feet.
When used in a JGOFS/GLOBEC dataset the depth is a best estimate; usually but not always calculated from pressure; calculated either from CTD pressure using Fofonoff and Millard (1982; UNESCO Tech Paper #44) algorithm adjusted for 1980 equation of state for seawater (EOS80) or simply equivalent to nominal depth as recorded during sampling if CTD pressure was unavailable.
Maximum temperature at the sampling site.
Sulfate Reduction Rate over 7 day incubation.
Standard deviation of rate_sevday.
Sulfate Reduction Rate of molybdate amended incubations (negative control).
Standard deviation of rate_inhib.
|Peter R. Girguis||Harvard University|
|Kiana L. Frank||Harvard University|
|Shannon Rauch||University of Hawaii at Manoa (SOEST)||✓|
BCO-DMO Project Info
|Project Title||Characterizing the distribution and rates of microbial sulfate reduction at Middle Valley hydrothermal vents|
|Acronym||Middle Valley Vents|
|Created||November 17, 2015|
|Modified||November 19, 2015|
This project characterizes 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°C in all three deposits. Pyrosequencing and functional gene abundance data reveal 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 play a role in sulfate reduction in warmer environments. The rates of sulfate reduction observed 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.
This project was funded, in part, by a C-DEBI Graduate Student Fellowship.