Community succession in an anaerobic long-chain paraffin-degrading consortium and impact on chemical and electrical microbially influenced iron corrosion.

Community compositional changes and the corrosion of carbon steel in the presence of different electron donor and acceptor combinations were examined with a methanogenic consortium enriched for its ability to mineralize paraffins. Despite cultivation in the absence of sulfate, metagenomic analysis revealed the persistence of several sulfate-reducing bacterial taxa. Upon sulfate amendment, the consortium was able to couple C28H58 biodegradation with sulfate reduction. Comparative analysis suggested that Desulforhabdus and/or Desulfovibrio likely supplanted methanogens as syntrophic partners needed for C28H58 mineralization. Further enrichment in the absence of a paraffin revealed that the consortium could also utilize carbon steel as a source of electrons. The severity of both general and localized corrosion increased in the presence of sulfate, regardless of the electron donor utilized. With carbon steel as an electron donor, Desulfobulbus dominated in the consortium and electrons from iron accounted for ∼92% of that required for sulfate reduction. An isolated Desulfovibrio spp. was able to extract electrons from iron and accelerate corrosion. Thus, hydrogenotrophic partner microorganisms required for syntrophic paraffin metabolism can be readily substituted depending on the availability of an external electron acceptor and a single paraffin-degrading consortium harbored microbes capable of both chemical and electrical microbially influenced iron corrosion.

Microbial activities in hydrocarbon-laden wastewaters: Impact on diesel fuel stability and the biocorrosion of carbon steel.

Anaerobic hydrocarbon biodegradation not only diminishes fuel quality, but also exacerbates the biocorrosion of the metallic infrastructure. While successional events in marine microbial ecosystems impacted by petroleum are well documented, far less is known about the response of communities chronically exposed to hydrocarbons. Shipboard oily wastewater was used to assess the biotransformation of different diesel fuels and their propensity to impact carbon steel corrosion. When amended with sulfate and an F76 military diesel fuel, the sulfate removal rate in the assay mixtures was elevated (26.8µM/d) relative to incubations receiving a hydroprocessed biofuel (16.1µM/d) or a fuel-unamended control (17.8µM/d). Microbial community analysis revealed the predominance of Anaerolineae and Deltaproteobacteria in F76-amended incubations, in contrast to the Beta- and Gammaproteobacteria in the original wastewater. The dominant Smithella-like sequences suggested the potential for syntrophic hydrocarbon metabolism. The general corrosion rate was relatively low (0.83 - 1.29±0.12mpy) and independent of the particular fuel, but pitting corrosion was more pronounced in F76-amended incubations. Desulfovibrionaceae constituted 50-77% of the sessile organisms on carbon steel coupons. Thus, chronically exposed microflora in oily wastewater were differentially acclimated to the syntrophic metabolism of traditional hydrocarbons but tended to resist isoalkane-laden biofuels.

Metabolic Capability of a Predominant Halanaerobium sp. in Hydraulically Fractured Gas Wells and Its Implication in Pipeline Corrosion.

Microbial activity associated with produced water from hydraulic fracturing operations can lead to gas souring and corrosion of carbon-steel equipment. We examined the microbial ecology of produced water and the prospective role of the prevalent microorganisms in corrosion in a gas production field in the Barnett Shale. The microbial community was mainly composed of halophilic, sulfidogenic bacteria within the order Halanaerobiales, which reflected the geochemical conditions of highly saline water containing sulfur species (S2O3 (2-), SO4 (2-), and HS(-)). A predominant, halophilic bacterium (strain DL-01) was subsequently isolated and identified as belonging to the genus Halanaerobium. The isolate could degrade guar gum, a polysaccharide polymer used in fracture fluids, to produce acetate and sulfide in a 10% NaCl medium at 37°C when thiosulfate was available. To mitigate potential deleterious effects of sulfide and acetate, a quaternary ammonium compound was found to be an efficient biocide in inhibiting the growth and metabolic activity of strain DL-01 relative to glutaraldehyde and tetrakis (hydroxymethyl) phosphonium sulfate. Collectively, our findings suggest that predominant halophiles associated with unconventional shale gas extraction could proliferate and produce sulfide and acetate from the metabolism of polysaccharides used in hydraulic fracturing fluids. These metabolic products might be returned to the surface and transported in pipelines to cause pitting corrosion in downstream infrastructure.

Anaerobic Biodegradation of Alternative Fuels and Associated Biocorrosion of Carbon Steel in Marine Environments.

Fuels that biodegrade too easily can exacerbate through-wall pitting corrosion of pipelines and tanks and result in unintentional environmental releases. We tested the biological stability of two emerging naval biofuels (camelina-JP5 and Fischer-Tropsch-F76) and their potential to exacerbate carbon steel corrosion in seawater incubations with and without a hydrocarbon-degrading sulfate-reducing bacterium. The inclusion of sediment or the positive control bacterium in the incubations stimulated a similar pattern of sulfate reduction with different inocula. However, the highest rates of sulfate reduction were found in incubations amended with camelina-JP5 [(57.2 ± 2.2)-(80.8 ± 8.1) µM/day] or its blend with petroleum-JP5 (76.7 ± 2.4 µM/day). The detection of a suite of metabolites only in the fuel-amended incubations confirmed that alkylated benzene hydrocarbons were metabolized via known anaerobic mechanisms. Most importantly, general (r(2) = 0.73) and pitting (r(2) = 0.69) corrosion were positively correlated with sulfate loss in the incubations. Thus, the anaerobic biodegradation of labile fuel components coupled with sulfate respiration greatly contributed to the biocorrosion of carbon steel. While all fuels were susceptible to anaerobic metabolism, special attention should be given to camelina-JP5 biofuel due to its relatively rapid biodegradation. We recommend that this biofuel be used with caution and that whenever possible extended storage periods should be avoided.

Roles of thermophilic thiosulfate-reducing bacteria and methanogenic archaea in the biocorrosion of oil pipelines.

Thermophilic sulfide-producing microorganisms from an oil pipeline network were enumerated with different sulfur oxyanions as electron acceptors at 55°C. Most-probable number (MPN) analysis showed that thiosulfate-reducing bacteria were the most numerous sulfidogenic microorganisms in pipeline inspection gauge (PIG) scrapings. Thiosulfate-reducing and methanogenic enrichments were obtained from the MPN cultures that were able to use yeast extract as the electron donor. Molecular analysis revealed that both enrichments harbored the same dominant bacterium, which belonged to the genus Anaerobaculum. The dominant archaeon in the methanogenic enrichment was affiliated with the genus Methanothermobacter. With yeast extract as the electron donor, the general corrosion rate by the thiosulfate-reducing enrichment (8.43 ± 1.40 milli-inch per year, abbreviated as mpy) was about 5.5 times greater than the abiotic control (1.49 ± 0.15 mpy), while the comparable measures for the methanogenic culture were 2.03 ± 0.49 mpy and 0.62 ± 0.07 mpy, respectively. Total iron analysis in the cultures largely accounted for the mass loss of iron measured in the weight loss determinations. Profilometry analysis of polished steel coupons incubated in the presence of the thiosulfate-reducing enrichment revealed 59 pits over an area of 71.16 mm(2), while only 6 pits were evident in the corresponding methanogenic incubations. The results show the importance of thiosulfate-utilizing, sulfide-producing fermentative bacteria such as Anaerobaculum sp. in the corrosion of carbon steel, but also suggest that Anaerobaculum sp. are of far less concern when growing syntrophically with methanogens.