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• Eutrophication enhances D. vulgaris planktonic growth and its sessile growth on Cu. • Cu MIC uniform corrosion and pitting increase with seawater eutrophication level. • Sessile cells on carbon steel MIC possess more cytochrome c than planktonic cells. • Cytochrome c levels in sessile and planktonic cells do not differ in Cu MIC. • Cu MIC by D. vulgaris belongs to metabolite MIC by secreted biogenic H 2 S. Seawater eutrophication increases the abundance of microbial communities and metabolic activities of microorganisms in seawater and potentially impacts microbiologically influenced corrosion (MIC). Copper as a common material in marine structures and nuclear waste containers faces serious MIC problems. This study investigated the copper MIC caused by Desulfovibrio vulgaris in anaerobic artificial seawater (ASW) with four eutrophication levels: pure ASW (PASW), oligotrophication ASW (OASW), mesotrophication ASW (MASW), and eutrophication ASW (EASW). It was found that the copper MIC increased along with the eutrophication level. The higher eutrophication led to an increase in the planktonic and Cu surface sessile D. vulgaris cell counts and H 2 S concentration in the headspace of anaerobic vials. The resultant weight loss and maximum pitting depth of copper in OASW were 2.0 and 2.4 times those in PASW, while their values in EASW were 2.8 and 4.2 times after 10 d of incubation, respectively. The experimental results combined with a bioenergetic analysis in this study indicated the copper MIC caused by D. vulgaris as belonging to biogenic H 2 S corrosion (i.e., metabolite MIC or M-MIC), which was further confirmed by the identical cytochrome c (Cyt c) (redox-active protein for extracellular electron transfer) expression levels of the planktonic D. vulgaris cells and sessile cells on copper. [Display omitted] [ABSTRACT FROM AUTHOR]

• Finite element method simulation shows highest stress at X80 U-bend bottom. • Uniform corrosion rate of X80 U-bend is 60% of that for unstressed square coupon. • Electrochemical tests corroborate weight loss and pitting data trends. • Sharp microcracks appear on X80 U-bend coupon after 12 weeks in D. vulgaris broth. • Pre-cracked X80 U-bend fails after 6 weeks of immersion in D. vulgaris broth. Sulfate reducing bacteria (SRB) are widely present in oil and gas industry, causing pitting corrosion on pipeline steel. Stress corrosion cracking (SCC) often occurs in the presence of mechanical stress before pitting perforation failure, leading to economic losses and even catastrophic accidents. In this study, stress distribution simulation using the finite element method (FEM), corrosion analysis techniques and electrochemical corrosion measurements were employed to investigate the SCC mechanism of X80 pipeline steel caused by Desulfovibrio vulgaris , which is a common SRB strain used in microbiologically influenced corrosion (MIC) studies. It was found that D. vulgaris MIC caused sharp microcracks on an X80 U-bend coupon after only 2 weeks of immersion at 37 °C in the deoxygenated ATCC 1249 culture medium inoculated with D. vulgaris. The X80 U-bend coupon's weight loss-based uniform corrosion rate for the 12 cm2 surface was 60% of that for the unstressed flat square coupon (2.3 mg cm−2 vs. 3.8 mg cm−2). This was likely because the square coupon had wide MIC pits, providing a larger effective surface area for more sessile cells (4.2×108 cells cm−2 on square coupon vs. 2.4×108 cells cm−2 on U-bend coupon) to attach and harvest more electrons. An SCC failure occurred on an X80 U-bend pre-cracked at the outer bottom after a 6-week immersion in the D. vulgaris broth. Apart from MIC damage, this could also be because D. vulgaris metabolism increased the availability hydrogen atoms on the steel surface, and promoted the diffusion of hydrogen atoms into the metal lattice, thus increasing the brittleness of the steel. D. vulgaris biofilm caused microcracks on X80 U-bend outer bottom surface after 14 days of incubation in (deoxygenated) ATCC 1249 culture medium at 37oC (left) with proposed SCC mechanism (right). [Display omitted] [ABSTRACT FROM AUTHOR]

• PilA gene regulates the formation of self-produced electrically conductive nanowires. • Strain ACL HF Δ pilA inhibits electron extraction from pure iron and 316L stainless steel. • Strain ACL HF ∆ omcS corrodes pure iron and 316L SS more than strain ACL HF Δ pilA. • e-Pili are a pivotal way of direct electron transfer by G. sulfurreducens from metal. Extracellular electron transfer (EET) plays a critical role in bioelectrochemical processes, allowing coupling between microorganisms and extracellular solid-state electrodes, metals, or other cells in energy metabolism. Previous studies have suggested a role for outer-surface c -type cytochromes in direct metal-to-microbe electron transfer by Geobacter sulfurreducens , a model electroactive bacterium. Here, we examined the possibility of other microbially produced electrical contacts by deleting the gene for PilA, the protein monomer that G. sulfurreducens assembles into electrically conductive protein nanowires (e-pili). Deleting pilA gene inhibited electron extraction from pure iron and 316L stainless steel up to 31% and 81%, respectively more than deleting the gene for the outer-surface cytochrome OmcS. This PilA-deficient phenotype, and the observation that relatively thick biofilms (21.7 μm) grew on the metal surfaces at multi-cell distances from the metal surfaces suggest that e-pili contributed significantly to microbial corrosion via direct metal-to-microbe electron transfer. These results have implications for the fundamental understanding of electron harvest via e-pili by electroactive microbes, their uses in bioenergy production, as well as in monitoring and mitigation of metal biocorrosion. [Display omitted] [ABSTRACT FROM AUTHOR]

• Riboflavin marginally enhances sessile cell growth of G. sulfurreducens ACL strain. • The strain with OMC gene deletion does not benefit from riboflavin addition. • c -Type cytochrome is linked to riboflavin acceleration of MIC pitting of 316L SS. • Electrochemical corrosion measurements support MIC acceleration observation. Microbes can cause or accelerate metal corrosion, leading to huge losses in corrosion damages each year. Geobacter sulfurreducens is a representative electroactive bacterium in many soils, sediments, and wastewater systems. It has been confirmed to directly extract electrons from elemental metals. However, little is known about the effect of electron shuttles in G. sulfurreducens corrosion on stainless steel. In this study, we report that exogenous flavins promote iron-to-microbe electron transfer, accelerating microbial corrosion. G. sulfurreducens caused 1.3 times deeper pits and increased electron uptake (with 2 times increase of i corr) from stainless steel when riboflavin was added to the culture medium. OmcS -deficient mutant data suggest that G. sulfurreducens utilizes riboflavin as a bound-cofactor in outer membrane c -type cytochromes. The finding that, in the presence of microbes, riboflavin can substantially accelerate corrosion highlights the role of flavin redox cycling for enhanced iron-to-microbe electron transfer by G. sulfurreducens and provides new insights in microbial corrosion. [Display omitted] [ABSTRACT FROM AUTHOR]

• Working electrode (WE) can be altered by potentiodynamic polarization in MIC. • Half-scans (from OCP) using one WE are far more accurate than continuous scan. • Continuous scan in either direction tends to incur large deviations in e corr and i corr. • Continuous scan compresses 1st half-scan curve voltage range and elongate the 2nd. • Repeated half-scans using the same WE are likely permissible in most MIC cases. [ABSTRACT FROM AUTHOR]

• Peptide A is a non-biocidal biofilm dispersal agent for biocide enhancement. • 20 ppm (w/w) THPS is insufficient to mitigate D. ferrophilus MIC of X80 steel. • 20 ppm THPS is enhanced by 100 ppb Peptide A, achieving 83% lower weight loss. • It also achieves 4-log extra sessile cell reduction compared with 20 ppm THPS. • 20 ppm THPS + 100 ppb Peptide A weight loss is similar to that for 50 ppm THPS. Tetrakis hydroxymethyl phosphonium sulfate (THPS) was enhanced by a 14-mer Peptide A, with its core 12-mer sequence mimicking part of Equinatoxin II protein, in the mitigation of sulfate reducing Desulfovibrio ferrophilus MIC (microbiologically influenced corrosion) of X80 carbon steel. Results proved that 50 ppm (w/w) THPS was sufficient to mitigate the D. ferrophilus biofilm, and its very agressive MIC (19.7 mg/cm2 in 7 days or 1.31 mm/a), but not 20 ppm THPS. To achieve effective mitigation at a low dosage of THPS, biofilm-dispersing Peptide A was added to 20 ppm THPS in the culture medium. Sessile cell counts were reduced by 2-log and 4-log after enhancement by 10 ppb and 100 ppb Peptide A, respectively. Enhancement efficiency (further reduction in corrosion rate) reached 69% for 10 ppb Peptide A and 83% for 100 ppb Peptide A compared with 20 ppm THPS alone treatment, indicating that Peptide A was a good biocide enhancer for THPS. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] The increasing utilization of titanium alloys in marine environments makes their microbiologically influenced corrosion study a timely matter. This work demonstrated that the corrosion of Ti-6Al-4 V alloy was accelerated by a marine bacterium Shewanella algae in 2216E medium with different Cl− level. Various electrochemical, pitting morphology and passive film analyses demonstrated that S. algae weakened the passive film, which made Cl− more aggressive. The synergy of those two factors caused considerable corrosion acceleration of the titanium alloy, leading to a maximum pit depth of 3.2 μm and corrosion current density of 26.5 nA cm−2 in 2216E medium with 3.50 % (w/w) Cl−. [ABSTRACT FROM AUTHOR]

In the oil and gas industry, microbiologically influenced corrosion (MIC) is a major threat to hydrotest, a procedure which is required to certify whether a pipeline can be commissioned. Seawater is frequently used as a hydrotest fluid. In this biofilm prevention lab study, an oilfield biofilm consortium was grown in an enriched artificial seawater anaerobically at 37 °C for 60 days. The combination of 100 ppm (w/w) 2,2-dibromo-3-nitrilopropionamide (DBNPA) + 100 nM (180 ppb) Peptide A (a biofilm dispersal agent) led to extra SRB (sulfate reducing bacteria), APB (acid producing bacteria) and GHB (general heterotrophic bacteria) sessile cell count reductions of 0.9-log, 0.8-log and 0.6-log, respectively, compared with the outcome obtained by using 100 ppm DBNPA only. The Peptide A enhancement also led to extra reductions of 44 % in weight loss, 43 % in maximum pit depth, and 54 % in corrosion current density. [ABSTRACT FROM AUTHOR]

The microbiologically influenced corrosion (MIC) mechanisms of copper by Pseudomonas aeruginosa as a typical strain of nitrate reducing bacteria (NRB) was investigated in this lab study. Cu was immersed in deoxygenated LB-NO 3 seawater inoculated with P. aeruginosa and incubated for 2 weeks. Results showed that this NRB caused pitting and uniform corrosion. The maximum pit depths after 7 d and 14 d in 125 mL anaerobic vials with 50 mL broth were 5.1 μm and 9.1 μm, accompanied by specific weight losses of 1.3 mg/cm2 (7 d) and 1.7 mg/cm2 (14 d), respectively. Electrochemical measurements corroborated weight loss and pit depth data trends. Experimental results indicated that extracellular electron transfer for nitrate reduction was the main MIC mechanism and ammonia secreted by P. aeruginosa could also play a role in the overall Cu corrosion process. [ABSTRACT FROM AUTHOR]

In this work, a surfactant, benzalkonium chloride (BAC), was used to study its effects on both the growth of Chlorella vulgaris and the corrosion caused by its biofilm. Experimental results indicated that BAC at a low concentration of 3 mg/L suppressed C. vulgaris growth and achieved 81 % corrosion inhibition based on weight loss reduction. The inhibition effects increased when the BAC dosage was increased. At 30 mg/L, the corrosion inhibition increased to 95 %. Electrochemical results supported surface pitting analysis, weight loss results data and confirmed the corrosion inhibition. [ABSTRACT FROM AUTHOR]

Acid producing bacterium Acetobacter aceti causes pitting corrosion of stainless steel (SS). This work investigated the enhanced resistance of 2205-Cu duplex stainless steel (DSS) against biocorrosion by A. aceti in comparison with 2205 DSS using electrochemical and surface analysis techniques. With the addition of Cu to 2205 DSS, biofilms on the 2205-Cu DSS surface were inhibited effectively. The largest pit depth on 2205-Cu DSS surface in the presence of A. aceti was 2.6 μm, smaller than 5.5 μm for 2205 DSS surface. The i corr was 0.42 ± 0.03 μA cm−2 for 2205-Cu DSS in the biotic medium, which was much lower than that for 2205 DSS (3.69 ± 0.65 μA cm−2). All the results indicated that the A. aceti biofilm was considerably inhibited by the release of Cu2+ ions from the 2205-Cu DSS matrix, resulting in the mitigation of biocorrosion by A. aceti. [ABSTRACT FROM AUTHOR]

Abstract Sulfate reducing bacteria (SRB) are often the culprits of microbiologically influenced corrosion (MIC) in anoxic environments because sulfate is a ubiquitous oxidant. MIC of carbon steel caused by SRB is the most intensively investigated topic in MIC because of its practical importance. It is also because biogenic sulfides complicate mechanistic SRB MIC studies, making SRB MIC of carbon steel is a long-lasting topic that has generated considerable confusions. It is expedient to think that biogenic H 2 S secreted by SRB acidifies the broth because it is an acid gas. However, this is not true because endogenous H 2 S gets its H+ from organic carbon oxidation and the fluid itself in the first place rather than an external source. Many people believe that biogenic H 2 S is responsible for SRB MIC of carbon steel. However, in recent years, well designed mechanistic studies provided evidence that contradicts this misconception. Experimental data have shown that cathodic electron harvest by an SRB biofilm from elemental iron via extracellular electron transfer (EET) for energy production by SRB is the primary cause. It has been demonstrated that when a mature SRB biofilm is subjected to carbon source starvation, it switches to elemental iron as an electron source and becomes more corrosive. It is anticipated that manipulations of EET related genes will provide genetic-level evidence to support the biocathode theory in the future. This kind of new advances will likely lead to new gene probes or transcriptomics tools for detecting corrosive SRB strains that possess high EET capabilities. [ABSTRACT FROM AUTHOR]

Abstract Microbiologically influenced corrosion (MIC) is caused by biofilms such as those of sulfate reducing bacteria (SRB). To mitigate MIC, biocide treatment is often needed. Tetrakis (hydroxymethyl) phosphonium sulfate (THPS) is an environmentally friendly biocide that is often used in the oil and gas industry. However, its prolonged use leads to biocide resistance, leading to dosage escalation. A biocide enhancer can be used to slow down the trend. In recent years, d -amino acids have been investigated as an enhancer for THPS and other biocides. Published works used anaerobic vials and flow devices, which could not reveal the real-time changes of the biocide treatment on corrosion. In this work, it was proven that the biocide enhancement effects of d -Phenylalanine (d -Phe) on THPS against the Desulfovibrio vulgaris biofilm on C1018 carbon steels could be assessed in real time using linear polarization resistance and electrochemical impedance spectroscopy to collaborate sessile cell count, weight loss and pitting depth data. The results showed that 500 ppm (w/w) d -Phe effectively enhanced 80 ppm THPS against MIC by the D. vulgaris (a corrosive SRB) biofilm. The sessile cell count and pit depth were all reduced with the enhancement of d -Phe. [ABSTRACT FROM AUTHOR]

Microbiologically influenced corrosion (MIC) is a major cause of corrosion damages, facility failures, and financial losses, making MIC an important research topic. Due to complex microbiological activities and a lack of deep understanding of the interactions between biofilms and metal surfaces, MIC occurrences and mechanisms are difficult to predict and interpret. Many theories and mechanisms have been proposed to explain MIC. In this review, the mechanisms of MIC are discussed using bioenergetics, microbial respiration types, and biofilm extracellular electron transfer (EET). Two main MIC types, namely EET-MIC and metabolite MIC (M-MIC), are discussed. This brief review provides a state of the art insight into MIC mechanisms and it helps the diagnosis and prediction of occurrences of MIC under anaerobic conditions in the oil and gas industry. [ABSTRACT FROM AUTHOR]

S32654 super austenitic stainless steel (SASS) is widely used in highly corrosive environments. However, its microbiologically influenced corrosion (MIC) behavior has not been reported yet. In this study, the corrosion behavior of S32654 SASS caused by a corrosive marine bacterium Pseudomonas aeruginosa was investigated using electrochemical measurements and surface analysis techniques. It was found that P. aeruginosa biofilm accelerated the corrosion rate of S325654 SASS, which was demonstrated by a negative shift of the open circuit potential ( E OCP ), a decrease of polarization resistance and an increase of corrosion current density in the culture medium. The largest pit depth of the coupons exposed in the P. aeruginosa broth for 14 days was 2.83 μm, much deeper than that of the control (1.33 μm) in the abiotic culture medium. It was likely that the P. aeruginosa biofilm catalyzed the formation of CrO 3 , which was detrimental to the passive film, resulting in MIC pitting corrosion. [ABSTRACT FROM AUTHOR]