Phylogenetic characterization of a corrosive consortium isolated from a sour gas pipeline

Effect of Pseudomonas aeruginosa Strain ZK Biofilm on the Mechanical and Corrosion Behavior of 316L Stainless Steel and α-brass

This research work aims to investigate the effect of the aerobic bacterium, Pseudomonas aeruginosa on the mechanical and electrochemical properties of the 316L stainless steel and α-brass. These properties of both the alloys were determined after 7 days of exposure to the controlled and inoculated media at 37°C. The microstructural and electrochemical test results revealed the deleterious effects of Pseudomonas aeruginosa. After exposure to the inoculated medium, the scanning electron microscopy (SEM) results showed the larger pitting and formation of relatively dense biofilm on α-brass compared to 316L stainless steel. The tensile strength and hardness of 316L stainless steel were slightly affected after exposure to the controlled and inoculated media. After exposure to the controlled medium and inoculated media, the tensile strength of the α-brass was least affected but a significant decrease in the hardness (from 165 HV to 124 HV) was observed due to the severe attack induced by the Pseudomonas aeruginosa. Similarly, the open-circuit potential of the 316L stainless steel in the inoculated medium was measured to be less active (−410 mV vs Ag/AgCl) than α-brass (−550 mV vs Ag/AgCl). In the inoculated medium, potentiodynamic polarization curves confirmed the severe attack of Pseudomonas aeruginosa on α-brass (7.15 × 10−2 mm/year) compared to 316L stainless steel which registered a corrosion rate of 5.14 × 10−4 mm/year.

Microbial corrosion of metals: The corrosion microbiome

Microbially catalyzed corrosion of metals is a substantial economic concern. Aerobic microbes primarily enhance Fe⁰ oxidation through indirect mechanisms and their impact appears to be limited compared to anaerobic microbes. Several anaerobic mechanisms are known to accelerate Fe⁰ oxidation. Microbes can consume H₂ abiotically generated from the oxidation of Fe⁰. Microbial H₂ removal makes continued Fe⁰ oxidation more thermodynamically favorable. Extracellular hydrogenases further accelerate Fe⁰ oxidation. Organic electron shuttles such as flavins, phenazines, and possibly humic substances may replace H₂ as the electron carrier between Fe⁰ and cells. Direct Fe⁰-to-microbe electron transfer is also possible. Which of these anaerobic mechanisms predominates in model pure culture isolates is typically poorly documented because of a lack of functional genetic studies. Microbial mechanisms for Fe⁰ oxidation may also apply to some other metals. An ultimate goal of microbial metal corrosion research is to develop molecular tools to diagnose the occurrence, mechanisms, and rates of metal corrosion to guide the implementation of the most effective mitigation strategies. A systems biology approach that includes innovative isolation and characterization methods, as well as functional genomic investigations, will be required in order to identify the diagnostic features to be gleaned from meta-omic analysis of corroding materials. A better understanding of microbial metal corrosion mechanisms is expected to lead to new corrosion mitigation strategies. The understanding of the corrosion microbiome is clearly in its infancy, but interdisciplinary electrochemical, microbiological, and molecular tools are available to make rapid progress in this field.

High-throughput sequencing approach in analysis of microbial communities colonizing natural gas pipelines

This study provides a deep modern insight into the phylogenetic diversity among bacterial consortia found in working and nonworking high‐methane natural gas pipelines located in Poland. The working pipeline was characterized by lower biodiversity (140–154 bacterial genera from 22 to 23 classes, depending on the source of the debris) in comparison to the off‐gas pipeline (169 bacterial genera from 23 classes). The sediment recovered from the working pipeline contained mostly DNA identified as belonging to the phylum Firmicutes (66.4%–45.9% operational taxonomic units [OTUs]), predominantly Bacillus (41.4%–31.1% OTUs) followed by Lysinibacillus (2.6%–1.5% OTUs) and Clostridium (2.4%–1.8% OTUs). In the nonworking pipeline, Proteobacteria (46.8% OTUs) and Cyanobacteria (27.8% OTUs) were dominant. Over 30% of the Proteobacteria sequences showed homologies to Gammaproteobacteria, with Pseudomonas (7.1%), Enhydrobacter (2.1%), Stenotrophomonas (0.5%), and Haempohilus (0.4%) among the others. Differences were noted in terms of the chemical compositions of deposits originating from the working and nonworking gas pipelines. The deposits from the nonworking gas pipeline contained iron, as well as carbon (42.58%), sulphur (15.27%), and oxygen (15.32%). This composition can be linked to both the quantity and type of the resident microorganisms. The presence of a considerable amount of silicon (17.42%), and of aluminum, potassium, calcium, and magnesium at detectable levels, may likewise affect the metabolic activity of the resident consortia in the working gas pipeline. All the analyzed sediments included both bacteria known for causing and intensifying corrosion (e.g., Pseudomonas, Desulfovibrio, Shewanella, Serratia) and bacteria that can protect the surface of pipelines against deterioration (e.g., Bacillus). Biocorrosion is not related to a single mechanism or one species of microorganism, but results from the multidirectional activity of multiple microbial communities. The analysis presented here of the state of the microbiome in a gas pipeline during the real gas transport is a particularly valuable element of this work.

Responses of Microbial Community Composition to Temperature Gradient and Carbon Steel Corrosion in Production Water of Petroleum Reservoir

Oil reservoir production systems are usually associated with a temperature gradient and oil production facilities frequently suffer from pipeline corrosion failures. Both bacteria and archaea potentially contribute to biocorrosion of the oil production equipment. Here the response of microbial populations from the petroleum reservoir to temperature gradient and corrosion of carbon steel coupons were investigated under laboratory condition. Carbon steel coupons were exposed to production water from a depth of 1809 m of Jiangsu petroleum reservoir (China) and incubated for periods of 160 and 300 days. The incubation temperatures were set at 37, 55, and 65°C to monitoring mesophilic, thermophilic and hyperthermophilic microorganisms associated with anaerobic carbon steel corrosion. The results showed that corrosion rate at 55°C (0.162 ± 0.013 mm year^-1) and 37°C (0.138 ± 0.008 mm year^-1) were higher than that at 65°C (0.105 ± 0.007 mm year^-1), and a dense biofilm was observed on the surface of coupons under all biotic incubations. The microbial community analysis suggests a high frequency of bacterial taxa associated with families Porphyromonadaceae, Enterobacteriaceae, and Spirochaetaceae at all three temperatures. While the majority of known sulfate-reducing bacteria, in particular Desulfotignum, Desulfobulbus and Desulfovibrio spp., were predominantly observed at 37°C; Desulfotomaculum spp., Thermotoga spp. and Thermanaeromonas spp. as well as archaeal members closely related to Thermococcus and Archaeoglobus spp. were substantially enriched at 65°C. Hydrogenotrophic methanogens of the family Methanobacteriaceae were dominant at both 37 and 55°C; acetoclastic Methanosaeta spp. and methyltrophic Methanolobus spp. were enriched at 37°C. These observations show that temperature changes significantly alter the microbial community structure in production fluids and also affected the biocorrosion of carbon steel under anaerobic conditions.

Bacillus sp. Acting as Dual Role for Corrosion Induction and Corrosion Inhibition with Carbon Steel (CS)

Present work investigated the role of five different bacteria species as a corrosion inducer as well as corrosion inhibitor with carbon steel (CS). We observed the ability of different bacteria species on the metal surface attachment, biofilm formation, and determined Peroxidase, Catalase enzyme activity in the detached biofilm from the CS surface. We found that each strain has diverse conduct for surface attachment like DS1 3.3, DS2 2.5, DS3 4.3, DS4 4.0, and DS5 4.71 log cfu/cm² and for biofilm 8.3 log cfu/cm². The enzyme Peroxidase, Catalase was found in huge concentration inside the biofilm Peroxidase was maximum for DS4 36.0 U/ml and least for DS3 19.54 U/ml. Whereas, Catalase was highest for DS4, DS5 70.14 U/ml and least 57.2 U/ml for DS2. Scanning electron microscopy (SEM) was conducted to examine the biofilm and electrochemical impedance spectroscopy (EIS) were utilized to observe corrosion in the presence of bacteria. The electrochemical results confirmed that DS1, DS3, DS4, and DS5 strains have statistically significant MIC-factors (Microbially Influenced Corrosion) of 5.46, 8.51, 2.36, and 1.04, while DS2 protective effect factor of 0.89. Weight reduction results with carbon steel likewise supports that corrosion was initiated by DS1 and DS3, while DS2 and DS5 have no any impact though with DS4 we watched less weight reduction however assumed no role in the corrosion. We established the relation of Peroxidase enzyme activity of the isolates. DS1, DS3 and having Peroxidase in the range 22.18, 19.54 U/ml which induce the corrosion whereas DS2 and DS5 having 28.57 and 27.0 U/ml has no any effect and DS4 36 U/ml has inhibitory effect, increasing concentration inhibiting the corrosion. For Catalase DS1, DS3 have 67.28, 61.57 U/ml which induce corrosion while DS2 and DS5 57.71 and 59.14 U/ml also has no effect whereas DS4 70.14 U/ml can inhibit corrosion. Results clearly express that in a specific range both enzymes can induce the corrosion. Our goals are to pursuit and locate the potential role of the enzyme in corrosion induction and inhibition. There is still further work is proceeded for the more profound perception.

Identification of the traditional and non-traditional sulfate-reducing bacteria associated with corroded ship hull

Pitting corrosion due to microbial activity is the most severe type of corrosion that occurs in ship hull. Since biogenic sulfide produced by sulfate-reducing bacteria (SRB) is involved in the acceleration of pitting corrosion of marine vessels, so it is important to collect information about SRB community involved in maritime vessel failure. We investigated the SRB community on corroded hull portion of the ship. With the use of common cultural method and 16S rDNA sequencing, ten bacteria with sulfate reduction ability were isolated and identified. They belonged to both traditional (Desulfovibrio, Desulfotomaculum) and non-traditional (Citrobacter) sulfate-reducing bacteria. All the isolates were able to produce a high amount of sulfide. However, only traditional isolates were showing the amplification for the SRB-specific gene, dsrAB. Further studies on corrosion potential of these two groups of bacteria showed that in spite of high sulfide and biofilm production by non-traditional SRB, they are less aggressive towards the mild steel compare to the traditional group.

Characterization of microfouling and corrosive bacterial community of a firewater distribution system

This investigation provides generic information on the culturable corrosive and the microfouling bacterial community in a firewater distribution system that uses freshwater. Conventional microbiological methods were used for the selective isolation of the major microfouling bacteria. The isolates were characterized by 16S rRNA gene sequencing and the biofilm as well as the corrosion characteristics of the isolates were evaluated. Pseudomonas aeruginosa and Bacillus cereus were predominantly observed in all the samples analysed. Denaturing gradient gel electrophoresis (DGGE) was carried out for the various samples of firewater system (FWS) and the high intensity bands were sequenced to identify the predominant bacteria. Bacterial groups such as Cyanobacteria, Proteobacteria, Actinobacteria, Bacteroidetes and Firmicutes were identified. Biofilm thickness was recorded using confocal scanning laser microscopy (CSLM). This was the first study to report Lysinibacillus fusiformis in a firewater system and its role in iron corrosion. Sulphidogenic bacteria Tissierella sp. and Clostridium bifermentans generated sulphides in the range of 400-900 ppm. Significant corrosion rates of carbon steel (CS) coupons were observed up to 4.3 mpy. C. bifermentans induced more localized corrosion in CS with a pit diameter of 50 μm. Overall, the data on the characterization of the fouling bacteria, their biofilm forming potential and subsequent metal deterioration studies supported in designing an effective water treatment program.

Corrosion of carbon steel by bacteria from North Sea offshore seawater injection systems: laboratory investigation

Influence of sulfidogenic bacteria, from a North Sea seawater injection system, on the corrosion of S235JR carbon steel was studied in a flow bioreactor; operating anaerobically for 100days with either inoculated or filtrated seawater. Deposits formed on steel placed in reactors contained magnesium and calcium minerals plus iron sulfide. The dominant biofilm-forming organism was an anaerobic bacterium, genus Caminicella, known to produce hydrogen sulfide and carbon dioxide. Open Circuit Potentials (OCP) of steel in the reactors was, for nearly the entire test duration, in the range -800<E(OCP)/mV (vs. SCE)<-700. Generally, the overall corrosion rate, expressed as 1/(Rp/Ω), was lower in the inoculated seawater though they varied significantly on both reactors. Initial and final corrosion rates were virtually identical, namely initial 1/(Rp/Ω)=2×10(-6)±5×10(-7) and final 1/(Rp/Ω)=1.1×10(-5)±2.5×10(-6). Measured data, including electrochemical noise transients and statistical parameters (0.05<Localized Index<1; -5<Skewness<-5; Kurtosis>45), suggested pitting on steel samples within the inoculated environment. However, the actual degree of corrosion could neither be directly correlated with the electrochemical data and nor with the steel corrosion in the filtrated seawater environment. Further laboratory tests are thought to clarify the noticed apparent discrepancies.

Bromate removal by anaerobic bacterial community: mechanism and phylogenetic characterization

A highly bromate resistant bacterial community and with ability for bromate removal was obtained from a sulphate-reducing bacteria enrichment consortium. This community was able to remove 96% of bromate and 99% of sulphate from an aqueous solution containing 40 μM bromate and 10 mM sulphate. Moreover, 93% of bromate was removed in the absence of sulphate. Under this condition bromate was reduced stoichiometrically to bromide. However, in the presence of sulphate only 88% of bromate was reduced to bromide. Although, bromate removal was not affected by the absence of sulphate, this anion promoted a modification on the structure of the bacterial community. Phylogenetic analysis of 16S rRNA gene showed that the community grown in the presence of bromate and sulphate was mainly composed by bacteria closely to Clostridium and Citrobacter genera, while the community grown in the absence of sulphate was predominantly composed by Clostridium genus. It is the first time that Clostridium and Citrobacter genera are reported as having bromate removal ability. Furthermore, bromate removal by the consortium predominantly composed by Clostridium and Citrobacter genera occurred by enzymatic reduction and by extracellular metabolic products, while the enzymatic process was the only mechanism involved in bromate removal by the consortium mainly composed by Clostridium genus.

Microbial fouling community analysis of the cooling water system of a nuclear test reactor with emphasis on sulphate reducing bacteria

Culture and molecular-based techniques were used to characterize bacterial diversity in the cooling water system of a fast breeder test reactor (FBTR). Techniques were selected for special emphasis on sulphate-reducing bacteria (SRB). Water samples from different locations of the FBTR cooling water system, in addition to biofilm scrapings from carbon steel coupons and a control SRB sample were characterized. Whole genome extraction of the water samples and SRB diversity by group specific primers were analysed using nested PCR and denaturing gradient gel electrophoresis (DGGE). The results of the bacterial assay in the cooling water showed that the total culturable bacteria (TCB) ranged from 10(3) to 10(5) cfu ml(-1); iron-reducing bacteria, 10(3) to 10(5) cfu ml(-1); iron oxidizing bacteria, 10(2) to 10(3) cfu ml(-1) and SRB, 2-29 cfu ml(-1). However, the counts of the various bacterial types in the biofilm sample were 2-3 orders of magnitude higher. SRB diversity by the nested PCR-DGGE approach showed the presence of groups 1, 5 and 6 in the FBTR cooling water system; however, groups 2, 3 and 4 were not detected. The study demonstrated that the PCR protocol influenced the results of the diversity analysis. The paper further discusses the microbiota of the cooling water system and its relevance in biofouling.

Effect of sodium bisulfite injection on the microbial community composition in a brackish-water-transporting pipeline

Pipelines transporting brackish subsurface water, used in the production of bitumen by steam-assisted gravity drainage, are subject to frequent corrosion failures despite the addition of the oxygen scavenger sodium bisulfite (SBS). Pyrosequencing of 16S rRNA genes was used to determine the microbial community composition for planktonic samples of transported water and for sessile samples of pipe-associated solids (PAS) scraped from pipeline cutouts representing corrosion failures. These were obtained from upstream (PAS-616P) and downstream (PAS-821TP and PAS-821LP, collected under rapid-flow and stagnant conditions, respectively) of the SBS injection point. Most transported water samples had a large fraction (1.8% to 97% of pyrosequencing reads) of Pseudomonas not found in sessile pipe samples. The sessile population of PAS-616P had methanogens (Methanobacteriaceae) as the main (56%) community component, whereas Deltaproteobacteria of the genera Desulfomicrobium and Desulfocapsa were not detected. In contrast, PAS-821TP and PAS-821LP had lower fractions (41% and 0.6%) of Methanobacteriaceae archaea but increased fractions of sulfate-reducing Desulfomicrobium (18% and 48%) and of bisulfite-disproportionating Desulfocapsa (35% and 22%) bacteria. Hence, SBS injection strongly changed the sessile microbial community populations. X-ray diffraction analysis of pipeline scale indicated that iron carbonate was present both upstream and downstream, whereas iron sulfide and sulfur were found only downstream of the SBS injection point, suggesting a contribution of the bisulfite-disproportionating and sulfate-reducing bacteria in the scale to iron corrosion. Incubation of iron coupons with pipeline waters indicated iron corrosion coupled to the formation of methane. Hence, both methanogenic and sulfidogenic microbial communities contributed to corrosion of pipelines transporting these brackish waters.

Diverse bacterial groups are associated with corrosive lesions at a Granite Mountain Record Vault (GMRV)

AIMS

This study applied culture-dependent and molecular approaches to examine the bacterial communities at corrosion sites at Granite Mountain Record Vault (GMRV) in Utah, USA, with the goal of understanding the role of microbes in these unexpected corrosion events.

METHODS AND RESULTS

Samples from corroded steel chunks, rock particles and waters around the corrosion pits were collected for bacterial isolation and molecular analyses. Bacteria cultivated from these sites were identified as members of Alphaproteobacteria, Gammaproteobacteria, Firmicutes and Actinobacteria. In addition, molecular genetic characterization of the communities via nested-polymerase chain reaction-denaturing gradient gel electrophoresis (DGGE) indicated the presence of a broad spectrum of bacterial groups, including Alphaproteobacteria, Betaproteobacteria, Deltaproteobacteria, Actinobacteria, Firmicutes and Bacteroidetes. However, neither cultivation nor molecular approaches identified sulfate-reducing bacteria (SRB), the bacteria commonly implicated as causative organisms were found associated with corrosive lesions in a process referred to as microbially influenced corrosion (MIC). The high diversity of bacterial groups at the corrosion sites in comparison with that seen in the source waters suggested to us a role for the microbes in corrosion, perhaps being an expression of a redox-active group of microbes transferring electrons, harvesting energy and producing biomass.

CONCLUSIONS

The corrosion sites contained highly diverse microbial communities, consistent with the involvement of microbial activities along the redox gradient at corrosion interface. We hypothesize an electron transport model for MIC, involving diverse bacterial groups such as acid-producing bacteria (APB), SRB, sulfur-oxidizing bacteria (SOB), metal-reducing bacteria (MRB) and metal-oxidizing bacteria (MOB).

SIGNIFICANCE AND IMPACT OF THE STUDY

The characterization of micro-organisms that influence metal-concrete corrosion at GMRV has significant implications for corrosion control in high-altitude freshwater environments. MIC provides a potential opportunity to further our understandings of extracellular electron transfer and interspecies communications.

Molecular analysis of microbial diversity in corrosion samples from energy transmission towers

Microbial diversity in corrosion samples from energy transmission towers was investigated using molecular methods. Ribosomal DNA fragments were used to assemble gene libraries. Sequence analysis indicated 10 bacterial genera within the phyla Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes. In the two libraries generated from corroded screw-derived samples, the genus Acinetobacter was the most abundant. Acinetobacter and Clostridium spp. dominated, with similar percentages, in the libraries derived from corrosion scrapings. Fungal clones were affiliated with 14 genera belonging to the phyla Ascomycota and Basidiomycota; of these, Capnobotryella and Fellomyces were the most abundant fungi observed. Several of the microorganisms had not previously been associated with biofilms and corrosion, reinforcing the need to use molecular techniques to achieve a more comprehensive assessment of microbial diversity in environmental samples.

Electrochemical checking of aerobic isolates from electrochemically active biofilms formed in compost

AIMS

To design a cyclic voltammetry (CV) procedure to check the electrochemical activity of bacterial isolates that may explain the electrochemical properties of biofilms formed in compost.

METHODS AND RESULTS

Bacteria catalysing acetate oxidation in garden compost were able to form electrochemically active biofilms by transferring electrons to an electrode under chronoamperometry. They were recovered from the electrode surface and identification of the isolates using 16S rRNA sequencing showed that most of them were Gammaproteobacteria, mainly related to Enterobacter and Pseudomonas spp. A CV procedure was designed to check the electrochemical activity of both groups of isolates. Preliminary CVs suggested that the bacteria were not responsible for the catalysis of acetate oxidation. In contrast, both groups of isolates were found to catalyse the electrochemical reduction of oxygen under experimental conditions that favoured adsorption of the microbial cells on the electrode surface.

CONCLUSIONS

Members of the genera Enterobacter and Pseudomonas were found to be able to catalyse the electrochemical reduction of oxygen.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study has shown the unexpected efficiency of Enterobacter and Pseudomonas spp. in catalysing the reduction of oxygen, suggesting a possible involvement of these species in biocorrosion, or possible application of these strains in designing bio-cathode for microbial fuel cells.

Biofilm formation in Desulfovibrio vulgaris Hildenborough is dependent upon protein filaments

Desulfovibrio vulgaris Hildenborough is a Gram-negative sulfate-reducing bacterium (SRB), and the physiology of SRBs can impact many anaerobic environments including radionuclide waste sites, oil reservoirs and metal pipelines. In an attempt to understand D. vulgaris as a population that can adhere to surfaces, D. vulgaris cultures were grown in a defined medium and analysed for carbohydrate production, motility and biofilm formation. Desulfovibrio vulgaris wild-type cells had increasing amounts of carbohydrate into stationary phase and approximately half of the carbohydrate remained internal. In comparison, a mutant that lacked the 200 kb megaplasmid, strain DeltaMP, produced less carbohydrate and the majority of carbohydrate remained internal of the cell proper. To assess the possibility of carbohydrate re-allocation, biofilm formation was investigated. Wild-type cells produced approximately threefold more biofilm on glass slides compared with DeltaMP; however, wild-type biofilm did not contain significant levels of exopolysaccharide. In addition, stains specific for extracellular carbohydrate did not reveal polysaccharide material within the biofilm. Desulfovibrio vulgaris wild-type biofilms contained long filaments as observed with scanning electron microscopy (SEM), and the biofilm-deficient DeltaMP strain was also deficient in motility. Biofilms grown directly on silica oxide transmission electron microscopy (TEM) grids did not contain significant levels of an exopolysaccharide matrix when viewed with TEM and SEM, and samples stained with ammonium molybdate also showed long filaments that resembled flagella. Biofilms subjected to protease treatments were degraded, and different proteases that were added at the time of inoculation inhibited biofilm formation. The data indicated that D. vulgaris did not produce an extensive exopolysaccharide matrix, used protein filaments to form biofilm between cells and silica oxide surfaces, and the filaments appeared to be flagella. It is likely that D. vulgaris used flagella for more than a means of locomotion to a surface, but also used flagella, or modified flagella, to establish and/or maintain biofilm structure.

Both sulfate-reducing bacteria and Enterobacteriaceae take part in marine biocorrosion of carbon steel

AIMS

In order to evaluate the part played in biocorrosion by microbial groups other than sulfate-reducing bacteria (SRB), we characterized the phylogenetic diversity of a corrosive marine biofilm attached to a harbour pile structure as well as to carbon steel surfaces (coupons) immersed in seawater for increasing time periods (1 and 8 months). We thus experimentally checked corroding abilities of defined species mixtures.

METHODS AND RESULTS

Microbial community analysis was performed using both traditional cultivation techniques and polymerase chain reaction cloning-sequencing of 16S rRNA genes. Community structure of biofilms developing with time on immersed coupons tended to reach after 8 months, a steady state similar to the one observed on a harbour pile structure. Phylogenetic affiliations of isolates and cloned 16S rRNA genes (rrs) indicated that native biofilms (developing after 1-month immersion) were mainly colonized by gamma-proteobacteria. Among these, Vibrio species were detected in majority with molecular methods while cultivation techniques revealed dominance of Enterobacteriaceae such as Citrobacter, Klebsiella and Proteus species. Conversely, in mature biofilms (8-month immersion and pile structure), SRB, and to a lesser extent, spirochaetes were dominant.

CONCLUSIONS

Corroding activity detection assays confirmed that Enterobacteriaceae (members of the gamma-proteobacteria) were involved in biocorrosion of metallic material in marine conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

In marine biofilms, metal corrosion may be initiated by Enterobacteriaceae.

Biodegradation of corrosion inhibitors and their influence on petroleum product pipeline

The present study enlightens the role of Bacillus cereus ACE4 on biodegradation of commercial corrosion inhibitors (CCI) and the corrosion process on API 5LX steel. Bacillus cereus ACE4, a dominant facultative aerobic species was identified by 16S rDNA sequence analysis, which was isolated from the corrosion products of refined diesel-transporting pipeline in North West India. The effect of CCI on the growth of bacterium and its corrosion inhibition efficiency were investigated. Corrosion inhibition efficiency was studied by rotating cage test and the nature of biodegradation of corrosion inhibitors was also analyzed. This isolate has the capacity to degrade the aromatic and aliphatic hydrocarbon present in the corrosion inhibitors. The degraded products of corrosion inhibitors and bacterial activity determine the electrochemical behavior of API 5LX steel.

Bacterial degradation and corrosion of naphtha in transporting pipeline

Five naphtha hydrocarbon-degrading bacteria including representative strains of the two classified species (Serratia marcescensAR1, Bacillus pumilusAR2, Bacillus carboniphilus AR3, Bacillus megaterium AR4, and Bacillus cereus AR5) were identified by 16S rDNA gene sequence in a naphtha-transporting pipeline. The naphtha-degrading strains were able to be involved in the corrosion process of API 5LX steel and also utilized the naphtha as the sole carbon source. The biodegradation of naphtha by the bacterial isolates was characterized by gas chromatography-mass spectrometry. Weight-loss measurement on the corrosion of API 5LX steel in the presence/absence of consortia grown in naphtha-water aqueous media was performed. The scanning electron microscope observation showed that the consortia were able to attack the steel API 5LX surface, creating localized corrosion (pit). The biodegradation of naphtha by the strains AR1, AR2, AR3, AR4, and AR5 showed biodegradation efficiency of about 76.21, 67.20, 68.78, 68.78, and 68.15, respectively. The role of degradation on corrosion has been discussed. This basic study will be useful for the development of new approaches for the detection, monitoring, and control of microbial corrosion in a petroleum product pipeline.

Role of Serratia marcescens ACE2 on diesel degradation and its influence on corrosion

A facultative anaerobic species Serratia marcescens ACE2 isolated from the corrosion products of diesel transporting pipeline in North West, India was identified by 16S rDNA sequence analysis. The role of Serratia marcesens ACE2 on biodegradation of diesel and its influence on the corrosion of API 5LX steel has been elucidated. The degrading strain ACE2 is involved in the process of corrosion of steel API 5LX and also utilizes the diesel as an organic source. The quantitative biodegradation efficiency (BE) of diesel was 58%, calculated by gas-chromatography-mass spectrum analysis. On the basis of gas-chromatography-mass spectrum (GC-MS), Fourier Transform infrared spectroscopy (FTIR) and X-ray diffractometer (XRD), the involvement of Serratia marcescens on degradation and corrosion has been investigated. This basic study will be useful for the development of new approaches for detection, monitoring and control of microbial corrosion.

Phylogenetic analysis of a biofilm bacterial population in a water pipeline in the Gulf of Mexico

The aim of this study was to assess the bacterial diversity associated with a corrosive biofilm in a steel pipeline from the Gulf of Mexico used to inject marine water into the oil reservoir. Several aerobic and heterotrophic bacteria were isolated and identified by 16S rRNA gene sequence analysis. Metagenomic DNA was also extracted to perform a denaturing gradient gel electrophoresis analysis of ribosomal genes and to construct a 16S rRNA gene metagenomic library. Denaturing gradient gel electrophoresis profiles and ribosomal libraries exhibited a limited bacterial diversity. Most of the species detected in the ribosomal library or isolated from the pipeline were assigned to Proteobacteria (Halomonas spp., Idiomarina spp., Marinobacter aquaeolei, Thalassospira sp., Silicibacter sp. and Chromohalobacter sp.) and Bacilli (Bacillus spp. and Exiguobacterium spp.). This is the first report that associates some of these bacteria with a corrosive biofilm. It is relevant that no sulfate-reducing bacteria were isolated or detected by a PCR-based method. The diversity and relative abundance of bacteria from water pipeline biofilms may contribute to an understanding of the complexity and mechanisms of metal corrosion during marine water injection in oil secondary recovery.

Dynamics of corrosion rates associated with nitrite or nitrate mediated control of souring under biological conditions simulating an oil reservoir

Representative microbial cultures from an oil reservoir and electrochemical techniques including potentiodynamic scan and linear polarization were used to investigate the time dependent corrosion rate associated with control of biogenic sulphide production through addition of nitrite, nitrate and a combination of nitrate-reducing, sulphide-oxidizing bacteria (NR-SOB) and nitrate. The addition of nitrate alone did not prevent the biogenic production of sulphide but the produced sulphide was eventually oxidized and removed from the system. The addition of nitrate and NR-SOB had a similar effect on oxidation and removal of sulphide present in the system. However, as the addition of nitrate and NR-SOB was performed towards the end of sulphide production phase, the assessment of immediate impact was not possible. The addition of nitrite inhibited the biogenic production of sulphide immediately and led to removal of sulphide through nitrite mediated chemical oxidation of sulphide. The real time corrosion rate measurement revealed that in all three cases an acceleration in the corrosion rate occurred during the oxidation and removal of sulphide. Amendments of nitrate and NR-SOB or nitrate alone both gave rise to localized corrosion in the form of pits, with the maximum observed corrosion rates of 0.72 and 1.4 mm year(-1), respectively. The addition of nitrite also accelerated the corrosion rate but the maximum corrosion rate observed following nitrite addition was 0.3 mm year(-1). Furthermore, in the presence of nitrite the extent of pitting was not as high as those observed with other control methods.

Characterization of bacterial community associated to biofilms of corroded oil pipelines from the southeast of Mexico

Microbial communities associated to biofilms promote corrosion of oil pipelines. The community structure of bacteria in the biofilm formed in oil pipelines is the basic knowledge to understand the complexity and mechanisms of metal corrosion. To assess bacterial diversity, biofilm samples were obtained from X52 steel coupons corroded after 40 days of exposure to normal operation and flow conditions. The biofilm samples were directly used to extract metagenomic DNA, which was used as template to amplify 16S ribosomal gene by PCR. The PCR products of 16S ribosomal gene were also employed as template for sulfate-reducing bacteria (SRB) specific nested-PCR and both PCR products were utilized for the construction of gene libraries. The V3 region of the 16S rRNA gene was also amplified to analyse the bacterial diversity by analysis of denaturing gradient gel electrophoresis (DGGE). Ribosomal library and DGGE profiles exhibited limited bacterial diversity, basically including Citrobacter spp., Enterobacter spp. and Halanaerobium spp. while Desulfovibrio alaskensis and a novel clade within the genus Desulfonatronovibrio were detected from the nested PCR library. The biofilm samples were also taken for the isolation of SRB. Desulfovibrio alaskensis and Desulfovibrio capillatus, as well as some strains related to Citrobacter were isolated. SRB consists in a very small proportion of the community and Desulfovibrio spp. were the relatively abundant groups among the SRB. This is the first study directly exploring bacterial diversity in corrosive biofilms associated to steel pipelines subjected to normal operation conditions.