Sulfate-reducing prokaryotes (SRP) producing hydrogen sulfide cause severe problems like microbial corrosion, souring and plugging in seawater-injected oil production systems. Adding nitrate to the injection water is a possible strategy to control the activity of SRP by favoring the growth of both heterotrophic, nitrate-reducing bacteria that outcompete SRP for substrates, and nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB). To assess the effects of nitrate addition, microbial diversity (Bacteria, Archaea) and SRP activity were studied in the production waters of a nitrate-treated and a non-treated high-temperature oil reservoir. At both sites, bacterial 16S rRNA gene clone libraries were dominated by members of the Firmicutes (75% and 43%, respectively). About 25% of the sequences from the non-treated system affiliated with deltaproteobacterial SRP, whereas they were only rarely found at the nitrate-treated site (2%). However, 5% of the sequences at this site were closely related to members of the epsilonproteobacterial NR-SOB (Sulfurospirillum spp.). Archaeal clone libraries were dominated by sequences affiliating with the Thermococcales (98%) and the hyperthermophilic, sulfate-reducing archaeon Archaeoglobus fulgidus (2%) at the non-treated site. In contrast, thermophilic methanogens (Methanothermococcus spp.) appeared to dominate the archaeal community at the nitrate-treated site. The presence of active SRP at the non-treated site was additionally supported by demonstrating their potential activity under pipeline (60°C), but not under oil reservoir conditions (80°C), indicating that the troublesome SRP were pipeline-derived. Consistent with the low amount of SRP, no activity could be shown for samples from the nitrate-treated system suggesting that SRP were inhibited by nitrate addition.
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12th International Symposium on Microbial Ecology (ISME-12), 2008