Molecular- and cultivation-based analyses of microbial communities in oil field water and in microcosms amended with nitrate to control H2S production |
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Authors: | Kumaraswamy Raji Ebert Sara Gray Murray R Fedorak Phillip M Foght Julia M |
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Institution: | (1) Biological Sciences, University of Alberta, Edmonton, AB, T6G 2E9, Canada;(2) Chemical and Materials Engineering, University of Alberta, Edmonton, AB, T6G 2V4, Canada; |
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Abstract: | Nitrate injection into oil fields is an alternative to biocide addition for controlling sulfide production (‘souring’) caused
by sulfate-reducing bacteria (SRB). This study examined the suitability of several cultivation-dependent and cultivation-independent
methods to assess potential microbial activities (sulfidogenesis and nitrate reduction) and the impact of nitrate amendment
on oil field microbiota. Microcosms containing produced waters from two Western Canadian oil fields exhibited sulfidogenesis
that was inhibited by nitrate amendment. Most probable number (MPN) and fluorescent in situ hybridization (FISH) analyses
of uncultivated produced waters showed low cell numbers (≤103 MPN/ml) dominated by SRB (>95% relative abundance). MPN analysis also detected nitrate-reducing sulfide-oxidizing bacteria
(NRSOB) and heterotrophic nitrate-reducing bacteria (HNRB) at numbers too low to be detected by FISH or denaturing gradient
gel electrophoresis (DGGE). In microcosms containing produced water fortified with sulfate, near-stoichiometric concentrations
of sulfide were produced. FISH analyses of the microcosms after 55 days of incubation revealed that Gammaproteobacteria increased
from undetectable levels to 5–20% abundance, resulting in a decreased proportion of Deltaproteobacteria (50–60% abundance).
DGGE analysis confirmed the presence of Delta- and Gammaproteobacteria and also detected Bacteroidetes. When sulfate-fortified
produced waters were amended with nitrate, sulfidogenesis was inhibited and Deltaproteobacteria decreased to levels undetectable
by FISH, with a concomitant increase in Gammaproteobacteria from below detection to 50–60% abundance. DGGE analysis of these
microcosms yielded sequences of Gamma- and Epsilonproteobacteria related to presumptive HNRB and NRSOB (Halomonas, Marinobacterium, Marinobacter, Pseudomonas and Arcobacter), thus supporting chemical data indicating that nitrate-reducing bacteria out-compete SRB when nitrate is added. |
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