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The protection of marine materials against corrosion using marine bacterial biofilms is a promising strategy. However, little is known about the mechanisms of this attractive corrosion prevention method. In this work, the corrosion behaviors of X80 carbon steel (CS) in the presence of three different marine Vibrio species were studied. The results demonstrated that all the three Vibrio spp. displayed significant corrosion protection with a weight loss reduction of up to 68%. Moreover, their corrosion prevention performance was tightly related to their abilities to form biofilms, which was in the order of Vibrio sp. EF187016 > Vibrio alginolyticus > Vibrio parahaemolyticus. To further investigate the corrosion prevention mechanism caused by marine biofilms, the extracellular polymeric substances (EPS) of Vibrio sp. EF187016 was extracted and added to 3.5 wt% NaCl for abiotic corrosion testing. The results suggested that the EPS inhibited corrosion, which means EPS can play a significant role in corrosion protection by biofilm. [ABSTRACT FROM AUTHOR]

The corrosion mechanism of carbon steel under deposit in the presence of sulfate reducing bacterium (SRB) Desulfotomaculum nigrificans was studied using surface analysis, weight loss and electrochemical measurements. Results showed that both the general corrosion and localized corrosion were considerably promoted by SRB under deposit. The corrosion rate of steel in the presence of SRB was approximately 6 times of that for the control according to the weight loss measurements. The maximum corrosion pit depth in the presence of SRB was approximately 7.7 times of that of the control. Both the anodic and cathodic reactions were significantly accelerated by SRB. A galvanic effect in the presence of SRB due to the heterogeneous biofilm led to serious localized corrosion. [ABSTRACT FROM AUTHOR]

In this work, the corrosion behavior and mechanism of carbon steel induced by extracellular polymeric substances (EPS) extracted from an iron-oxidizing bacterium culture were studied using surface analysis and electrochemical measurements in 3.5 wt% NaCl solutions. Results of electrochemical measurements showed that 7 day-old EPS at 240 mg L-1 inhibited the corrosion of carbon steel, especially after the EPS solution was heat treated to deactivate the enzymes in the EPS. However, 7 day-old EPS at much higher and much lower concentrations accelerated corrosion. Furthermore, 14 day-old EPS and 28 day-old EPS at 240 mg L-1 also accelerated corrosion. [ABSTRACT FROM AUTHOR]

In this paper, the effect of a magneticfield (MF) on biomineralization and corrosion behavior of Q235 carbon steel were studied using surface analysis, weight loss and electrochemical measurements. Experimental results showed that MF inhibited the growth of iron-oxidizing bacteria (IOB) and the corrosion of Q235 carbon steel. MF reduced the largest pit depth by half, while it reduced pit population density from 50 pits cm −2 to 10 pits cm −2 . MF also altered the morphology of biomineralization film, leading to the formation of a more compact biomineralization film which contributed to the lower corrosion rate. [ABSTRACT FROM AUTHOR]

The corrosion behavior of carbon steel was investigated in the presence of SRB and IOB separately in their respective culture media and in the mixed culture of SRB and IOB in artificially produced water with 4.2 mg/L dissolved oxygen. The results showed that IOB inhibited the growth of planktonic SRB, but promoted the growth of sessile SRB when SRB was cultured together with IOB. The mixture of SRB and IOB had a synergistic effect enhancing the pitting corrosion of the coupons. The limited amount of dissolved oxygen played a key role in the formation of corrosion products. [ABSTRACT FROM AUTHOR]

Desulfovibrio ferrophilus (IS5) corrosion of X65 carbon steel was impacted by gravity. Six o'clock position (6P) had the highest sessile count due to gravity assisting planktonic cell settling in early biofilm formation, leading to most severe static corrosion followed by 9P and 12P. The 7-d weight loss at 6P was 49.6 ± 4.4 mg/cm2 (3.3 mm/a in uniform corrosion rate) followed by 9P with 35.7 ± 2.6 mg/cm2 (2.4 mm/a) and 12P with 20.5 ± 5.5 mg/cm2 (1.4 mm/a). The trend was supported by electrochemical measurements. The weight loss differences reduced considerably when there was agitation, supporting the gravity hypothesis. • Early SRB biofilm growth is impacted by gravity, favoring 6 o'clock position (6P). • The biofilm sessile cell count sequence is 6P > 9P (side way) >12P (face down). • Weight loss and pit depth sequences after 7-day SRB incubation are 6P > 9P > 12P. • 6P has a uniform corrosion rate of 3.3 mm/a vs. 1.4 mm/a for 12P for 7-d incubation. • Agitation lowered weight loss differences, supporting gravity impact hypothesis. [ABSTRACT FROM AUTHOR]

• Rough surface finish on a coupon facilitates early biofilm development. • Highly-corrosive D. ferrophilus IS5 provides large weight losses. • 36 grit has higher sessile cell count and higher weight loss than 600 grit at 7 d. • These differences wane over time as suggested by 30 d data. • Electrochemical data support weight loss data with additional transient information. Carbon steel microbiologically influenced corrosion (MIC) by sulfate reducing bacteria (SRB) is known to occur via extracellular electron transfer (EET). A higher biofilm sessile cell count leads to more electrons being harvested for sulfate reduction by SRB in energy production. Metal surface roughness can impact the severity of MIC by SRB because of varied biofilm attachment. C1018 carbon steel coupons (1.2 cm2 top working surface) polished to 36 grit (4.06 μm roughness which is relatively rough) and 600 grit (0.13 μm) were incubated in enriched artificial seawater inoculated with highly corrosive Desulfovibrio ferrophilus IS5 at 28 ℃ for 7 d and 30 d. It was found that after 7 d of SRB incubation, 36 grit coupons had a 11% higher sessile cell count at (2.0 ± 0.17) × 108 cells/cm2, 52% higher weight loss at 22.4 ± 5.9 mg/cm2 (1.48 ± 0.39 mm/a uniform corrosion rate), and 18% higher maximum pit depth at 53 μm compared with 600 grit coupons. However, after 30 d, the differences diminished. Electrochemical tests with transient information supported the weight loss data trends. This work suggests that a rougher surface facilitates initial biofilm establishment but provides no long-term advantage for increased biofilm growth. [ABSTRACT FROM AUTHOR]

• More Fe2+ leads to better planktonic and sessile Desulfovibrio vulgaris growth. • More Fe2+ increases dissolved H 2 S concentration despite increased FeS precipitation. • More Fe2+ in the culture medium increases carbon steel weight loss and pit depth. • With more Fe2+, increased corrosion is primarily attributed to more sessile cells. • Electrochemical measurements corroborate weight loss and pit depth data. Ferrous ion (Fe2+) in a sulfate reducing bacteria (SRB) culture medium is known to enhance microbiologically influenced corrosion (MIC) of carbon steel, but the underlining mechanism is controversial. This work showed that it was due to better sessile cell growth that was likely attributed to Fe2+ detoxification of H 2 S. Two hundred ppm (w/w) initial Fe2+ in the ATCC 1249 medium achieved a 4.7 times higher Desulfovibrio vulgaris sessile cell count and 5.0 times higher C1018 carbon steel weight loss, compared to 20 ppm. Linear polarization resistance, electrochemical impedance spectroscopy and potentiodynamic polarization measurements corroborated weight loss and pitting data trends. [ABSTRACT FROM AUTHOR]

Highlights • D. vulgaris is pre-grown on C1018 carbon steel coupons before the starvation test. • Carbon source starvation weakens the SRB biofilm but still increases weight loss. • Weight loss is 6.6 mg/cm2 for 20% carbon source vs. 3.3 mg/cm2 for 100% after 10 d. • Pit depth and electrochemical measurement data corroborate weight loss trend. • Iron corrosion by SRB belongs to extracellular electron transfer MIC (EET-MIC). Abstract Microbiologically influenced corrosion (MIC) of carbon steel by sulfate reducing bacterium (SRB) Desulfovibrio vulgaris under organic carbon starvation was investigated using electrochemical methods to support weight loss and pitting data. 20% carbon source led to the highest weight loss (6.6 mg/cm2), while 100% had the lowest (3.3 mg/cm2) after 10 days. Linear polarization resistance and electrochemical impedance spectrometry data confirmed the weight loss and pitting data trends. The data in this work support the theory that carbon steel corrosion by SRB is due to electron harvest from extracellular iron oxidation by SRB, which belongs to extracellular electron transfer MIC (EET-MIC). [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Molecular simulation confirms that sodium pyrithione (SPT) inhibits iron corrosion. • SPT is found to inhibit planktonic and sessile sulfate reducing bacteria (SRB). • SRB corrosion rate in simulated oilfield produced water is reduced by SPT. • SRB corrosion weight loss data are corroborated by electrochemical measurements. Abstract Anti–bacterial and anti–corrosion properties of sodium pyrithione (SPT) were studied using experimental methods and quantum chemical calculations. SPT at 80 mg/L reduced planktonic and sessile sulfate reducing bacteria (SRB) on X80 carbon steel to undetectable levels. The corrosion inhibition efficiency of SPT against microbiologically influenced corrosion exceeded 80% based on weight loss, which was corroborated by electrochemical data. Molecular modeling showed that SPT molecule provided electrons to the unoccupied orbitals of the Fe surface with a large binding energy of SPT on the Fe (1 1 0) plane, which favored SPT adsorption on the carbon steel. [ABSTRACT FROM AUTHOR]

Highlights • Archaeoglobus fulgidus is a very corrosive sulfate reducing archaeon at 80 °C. • Pre-grown A. fulgidus biofilm is more corrosive under carbon source starvation. • Its corrosion type is extracellular electron transfer MIC (EET-MIC). • This archaeon is capable of using elemental iron as an electron donor. • Linear polarization resistance data support MIC weight loss and pit depth data. Abstract Mature sulfate reducing archaeon (Archaeoglobus fulgidus) biofilm at 80 °C was found more corrosive against C1018 carbon steel under organic carbon starvation. After 3-day pre-growth in enriched artificial seawater medium (EASW), C1018 coupons with biofilms were placed in fresh EASW with reduced carbon source levels for an additional 7 days of incubation. Coupon weight losses were 0.9 mg/cm2, 2.0 mg/cm2 and 1.4 mg/cm2 for this subsequent 7-day starvation period, corresponding to 0%, 90% and 100% carbon source reductions, respectively. Electrochemical tests corroborated the weight loss data, providing evidence for the utilization of elemental iron as electron donor through extracellular electron transfer. [ABSTRACT FROM AUTHOR]

Enhanced oil recovery typically relies on injection of seawater mixed with chemicals to increase reservoir pressure. A polymer such as partially hydrolyzed polyacrylamide (HPAM) is often added to increase viscosity. In this work, an oilfield biofilm consortium was found to utilize a commercial HPAM-based polymer. The polymer at 1000 ppm (w/w) promoted the growth of planktonic cells and sulfate reducing bacteria sessile cells in an artificial seawater medium during a 30-day incubation period in anaerobic vials. The polymer utilization led to 34.5% viscosity loss and more severe microbiologically influenced corrosion weight loss and pitting against C1018 carbon steel. [ABSTRACT FROM AUTHOR]

The role of biogenic H 2 S in the microbiologically influenced corrosion (MIC) of carbon steel was investigated. Desulfovibrio vulgaris (ATCC 7757), a sulfate reducing bacterium, was tested against C1018 carbon steel in anaerobic vials with three different sizes, each filled with 40 mL of ATCC 1249 culture medium, providing headspace volumes of 10 mL, 85 mL and 160 mL, respectively for H 2 S to escape. Results showed that a larger headspace led to a lower H 2 S concentration in the culture medium, and this increased the sessile cell count and made the iron sulfide film thinner, resulting in increased MIC. [ABSTRACT FROM AUTHOR]

Electron transfer is a rate-limiting step in microbiologically influenced corrosion (MIC) caused by microbes that utilize extracellular electrons. Cross-cell wall electron transfer is necessary to transport the electrons released from extracellular iron oxidation into the cytoplasm of cells. Electron transfer mediators were found to accelerate the MIC caused by sulfate reducing bacteria. However, there is no publication in the literature showing the effect of electron transfer mediators on MIC caused by nitrate reducing bacteria (NRB). This work demonstrated that the corrosion of anaerobic Pseudomonas aeruginosa (PAO1) grown as a nitrate reducing bacterium biofilm on C1018 carbon steel was enhanced by two electron transfer mediators, riboflavin and flavin adenine dinucleotide (FAD) separately during a 7-day incubation period. The addition of either 10 ppm (w/w) (26.6 μM) riboflavin or 10 ppm (12.7 μM) FAD did not increase planktonic cell counts, but they increased the maximum pit depth on carbon steel coupons considerably from 17.5 μm to 24.4 μm and 25.0 μm, respectively. Riboflavin and FAD also increased the specific weight loss of carbon steel from 2.06 mg/cm 2 to 2.34 mg/cm 2 and 2.61 mg/cm 2 , respectively. Linear polarization resistance, electrochemical impedance spectroscopy and potentiodynamic polarization curves all corroborated the pitting and weight loss data. [ABSTRACT FROM AUTHOR]

This work showed that a wild-type Pseudomonas aeruginosa (PAO1) grown as a nitrate reducing bacterium biofilm on C1018 carbon steel was more corrosive under organic carbon source starvation. P. aeruginosa biofilms were pre-grown for 2 days to achieve maturity before the culture media were changed to fresh culture media with 100% (as in the standard medium), 10%, and 0% organic carbons for subsequent 7-day incubation. Biofilms with 100%, 10%, and 0% organic carbons caused maximum pit depths of 5.4 μm, 10.6 μm, and 17.0 μm, respectively. Weight loss, linear polarization resistance and electrochemical impedance spectroscopy data corroborated the pitting data. [ABSTRACT FROM AUTHOR]

Abstract: Nitrate injection is used to suppress reservoir souring in oil and gas fields caused by Sulfate Reducing Bacteria (SRB) through promotion of nitrate respiration by Nitrate Reducing Bacteria (NRB). However, it is not well publicized that nitrate reduction by NRB can cause Microbiologically Influenced Corrosion (MIC) because nitrate reduction coupled with iron oxidation is thermodynamically favorable. NRB benefits bioenergetically from this redox reaction under biocatalysis. This work showed that the Bacillus licheniformis biofilm, when grown as an NRB biofilm, caused a 14.5μm maximum pit depth and 0.89mg/cm2 normalized weight loss against C1018 carbon steel in one-week lab tests. [Copyright &y& Elsevier]

• Data confirm extracellular electron transfer MIC (EET-MIC) mechanism. • Riboflavin enhances Desulfovibrio ferrophilus IS5 EET-MIC considerably. • Very high carbon steel pitting corrosion rate for a pure-strain SRB is shown. • H 2 evolution data rule out acid and H 2 S corrosion as significant contributors. • D. ferrophilus biofilm starts to respond to riboflavin injection within minutes. EET (extracellular electron transfer) is behind MIC (microbiologically influenced corrosion) of carbon steel by SRB (sulfate reducing bacteria). This work evaluated 20 ppm (w/w) riboflavin (an electron mediator) acceleration of C1018 carbon steel MIC by Desulfovibrio ferrophilus IS5 in enriched artificial seawater (EASW) after 7-d incubation in anaerobic vials at 28 °C. Twenty ppm riboflavin did not significantly change cell growth or alter the corrosion product varieties, but it led to 52% increase in weight loss and 105% increase in pit depth, compared to the control without 20 ppm riboflavin. With 20 ppm riboflavin supplement in EASW, D. ferrophilus yielded weight loss-based corrosion rate of 1.57 mm/y (61.8 mpy), and pit depth growth rate of 2.88 mm/y (113 mpy), highest reported for short-term pure-strain SRB MIC of carbon steel. Electrochemical tests in 450 mL glass cells indicated that the biofilm responded rather quickly to the riboflavin injection (20 ppm in broth) to the culture medium. Polarization resistance (R p) began to decrease within minutes after injection. Within 2 h, the riboflavin injection led to 31% decrease in R p and 35% decrease in R ct + R f from electrochemical impedance spectroscopy (EIS). The Tafel corrosion current density increased 63% 2 h after the injection. [ABSTRACT FROM AUTHOR]