The study aimed to determine whether nitrate-utilizing sulfate-reducing bacteria (SRB) thrive in
the Hawtah oil field produced water re-injection system (PWRI). Bacterial populations were
recovered through enrichments in selective growth media from samples collected at different
locations in PWRI. Characterization of purified Hawtah field SRB isolates using 16S rRNA
gene-based phylogeny, revealed the presence of an isolate, coded DD-H SRB, showing a high
16S rRNA sequence similarity (99%) with Desulfovibrio desulfuricans spp. desulfuricans. The
change from sulfate to nitrate reduction was tested using the DD-H SRB isolate and a “wild”
Hawtah SRB enrichment in the laboratory batch culture experiments. Control culture
comprised a tri-species mixture of pure Desulfovibrio strains. Both, the DD-H SRB isolate and
the control SRB culture, when exposed to a gradually decreasing concentration of sulfate and
a concurrently increasing concentration of nitrate over a 40-day period, changed slowly from
sulfate to nitrate respiration. Upon inoculation into a sulfate-free medium, fast nitrate reduction
was observed. In the “wild” Hawtah field SRB population, the transition to nitrate reduction was
faster. The functional gene aprA, coding for adenosine-5-phosphosulfate (APS)-reductase
enzyme, which is found in all known SRB genera, was present in all tested cultures grown with
nitrate as a sole electron acceptor.
Keywords: Sulfate-reducing bacteria, nitrate treatment, oil-field microbiology, aprAB functional
gene, nitrate reduction, Desulfovibrio desulfuricans.