2 Next-Generation Sedimentary Systems Geobiology

Monday, 18 April 2016
8:00 AM - 10:20 AM
Lincoln Room

MICROBIAL CONTROLS ON SULFUR ISOTOPE PARTITIONING UNDER LOW-NUTRIENT CONDITIONS

Paper number: 2-3
Program: Theme Sessions
Time: 8:40 AM – 9:00 AM

Authors

Abstract

Microbial reduction of sulfate is ubiquitous in anoxic environments across the geosphere. Respiration rates of sulfate reducing bacteria (SRB) are commonly inferred in natural, nutrient-limited environments using the characteristic partitioning of stable S isotopes. However, most laboratory experiments use artificially high nutrient (eutrophic) conditions to constrain the fractionation factor through substantial S isotope partitioning. We hypothesize that under natural, nutrient-poor (oligotrophic) conditions, S isotope partitioning carried out by SRB will produce distinct S partitioning when compared to these artificially enhanced conditions. Natural conditions also promote a constant microbial population helping to simplify the δ34S signal.

Our method incorporates eight anoxic bioreactors charged with natural concentrations of nutrients and a living culture of desulfovibrio vulgaris, a common SRB. The reactions are driven by additions of an electron donor, formate, continuously added at a range of input concentrations in order to precisely control respiration rates in each community. Concentrations of sulfate and formate are monitored via ion chromatography and used to determine sulfate reduction rates. Comparing the δ34S of the residual sulfate pool to the δ34S of the initial sulfate pool yields the S fractionation factor carried out by desulfovibrio vulgaris.

Based on our results, we hypothesize that mass dependent sulfate reduction under oligotrophic conditions is coupled to a mass dependence on the half-saturation constant exhibited by SRB. Such a relationship could provide pertinent information about a given microbial community using routine field sampling techniques paired with S isotope analysis. Knowledge of the subsurface microbial community and its ability to reduce chemical species is critical for safe storage of contaminants as well as stewardship of newly discovered and preexisting hydrologic regimes.

Geological Society of America Abstracts with Programs. Vol. 48, No. 5

doi: 10.1130/abs/2016NC-275583

© Copyright 2016 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.