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Engineering living functional biofilms offers an ecofriendly and efficient technique for the corrosion protection of metallic materials in marine environments. Its firm attachment to the metal surface is a key step to effectively improve the corrosion protection. Herein, engineered Escherichia coli biofilm with strong metal binding ability is constructed by genetically appending a metal binding domain (MBD) to extracellular amyloids. The engineered living biofilm improved the corrosion resistance of X70 carbon steel. Moreover, a biofilm‐induced mineralization layer, mainly composed of calcite, is formed on the X70 surface, which provided a stable corrosion barrier. At the end of 7‐days immersion, the icorr decreased from 5.1 ± 0.4 µA cm−2 without biofilm to 0.5 ± 0.1 µA cm−2 with E. coli MBD biofilm, resulting in a corrosion inhibition efficiency of 90.2%. It also demonstrated the corrosion protection effect for 304 stainless steel, suggesting possible broad applications of the engineered biofilm. The application of synthetic biology offers a novel approach in the development of anti‐corrosion technologies in water environments. [ABSTRACT FROM AUTHOR]

MIC (microbiologically influenced corrosion) is problematic in many industries, especially in the oil and gas industry. In this work, N80 carbon steel for pipelines was tested with 26Cr3Mo chromium pipeline steel for comparison in SRB (sulfate-reducing bacterium) MIC mitigation using a THPS (tetrakis hydroxymethyl phosphonium sulfate)-based commercial biocide (Biotreat 5475 with 75–80% THPS by mass). Peptide A, a nature-mimicking synthetic cyclic peptide (cys-ser-val-pro-tyr-asp-tyr-asn-trp-tyr-ser-asn-trp-cys) with biofilm dispersal ability was used as a biocide enhancer. Metal coupons covered with 3-d old Desulfovibrio ferrophilus IS5 biofilms were immersed in different biocide solutions. After 1-h treatment, 200 ppm Biotreat 5475, 200 ppm Biotreat 5475 + 200 nM (360 ppb) Peptide A, and 400 ppm Biotreat 5475 achieved 0.5-log, 1.7-log and 1.9-log reductions in sessile cell count on N80, and 0.7-log, 1.7-log, and 1.8-log on 26Cr3Mo, respectively. The addition of 200 nM Peptide A cut the THPS biocide dosage by nearly half. Biocide injection tests in electrochemical glass cells after 1 h exhibited 15%, 70%, and 72% corrosion inhibition efficiency (based on corrosion current density) on N80, and 27%, 79%, 75% on 26Cr3Mo, respectively. Linear polarization resistance and electrochemical impedance spectrometry results also indicated antimicrobial efficacies. [ABSTRACT FROM AUTHOR]

NiMo (nickel-molybdenum) and NiMo with embedded CeO2 nanoparticles (NPs; 100 nm) were tested as antimicrobial coatings (~15 μm thickness) on titanium (Ti) surfaces using an electrochemical process for heat exchanger applications onboard marine vessels. Preliminary static biofouling and biocorrosion (also known as microbiologically influenced corrosion) assessments were carried out in glass bottles using pure-culture Desulfovibrio vulgaris , a sulfate-reducing bacterium (SRB), in deoxygenated ATCC 1249 medium at 37°C, and using an alga (Chlorella vulgaris) mixed with general heterotrophic bacteria (GHB) in enriched artificial seawater at 28°C. It was found that the coating containing NiMo/CeO2 NPs were much more effective than NiMo in preventing SRB biofilm formation with an efficacy of 99% reduction in D. vulgaris sessile cells after 21 day incubation. The coating also exhibited a 50% lower corrosion current density compared to the uncoated Ti against SRB corrosion. Both NiMo and NiMo/CeO2 NP coatings achieved 99% reduction in sessile algal cells. Confocal laser scanning microscopy (CLSM) biofilm images indicated a large reduction of sessile GHB cells. The CLSM images also confirmed the biocidal kill effects of the two coatings. Unlike polymer coatings, the "metallic" coatings are heat conductive. Thus, the corrosion resistant antifouling coatings are suitable for heat exchanger applications. [ABSTRACT FROM AUTHOR]

Biocorrosion, also called microbiologically influenced corrosion (MIC), is a common operational threat to many industrial processes. It threatens carbon steel, stainless steel and many other metals. In the bioprocessing industry, reactor vessels in biomass processing and bioleaching are prone to MIC. MIC is caused by biofilms. The formation and morphology of biofilms can be impacted by fluid flow. Fluid velocity affects biocide distribution and MIC. Thus, assessing the efficacy of a biocide for the mitigation of MIC under flow condition is desired before a field trial. In this work, a benchtop closed flow loop bioreactor design was used to investigate the biocide mitigation of MIC of C1018 carbon steel at 25 °C for 7 days using enriched artificial seawater. An oilfield biofilm consortium was analyzed using metagenomics. The biofilm consortium was grown anaerobically in the flow loop which had a holding vessel for the culture medium and a chamber to hold C1018 carbon steel coupons. Peptide A (codename) was a chemically synthesized cyclic 14-mer (cys-ser-val-pro-tyr-asp-tyr-asn-trp-tyr-ser-asn-trp-cys) with its core 12-mer sequence originated from a biofilm dispersing protein secreted by a sea anemone which possesses a biofilm-free exterior. It was used as a biocide enhancer. The combination of 50 ppm (w/w) THPS (tetrakis hydroxymethyl phosphonium sulfate) biocide + 100 nM (180 ppb by mass) Peptide A resulted in extra 1-log reduction in the sulfate reducing bacteria (SRB) sessile cell count and the acid producing bacteria (APB) sessile cell count compared to 50 ppm THPS alone treatment. Furthermore, with the enhancement of 100 nM Peptide A, extra 44% reduction in weight loss and 36% abatement in corrosion pit depth were achieved compared to 50 ppm THPS alone treatment. [ABSTRACT FROM AUTHOR]

Three types of stainless steel (304 SS, 410 SS, and 2205 SS) were evaluated for their corrosion behaviors in microbiologically influenced corrosion (MIC) by Desulfovibrio ferrophilus strain IS5, a relatively new and very corrosive sulfate-reducing bacteria (SRB) strain. The incubation lasted for 7 days in enriched artificial seawater at 28°C and the results showed that 410 SS had a rather large weight loss (6.2 mg/cm2) and a maximum pit depth (118 µm), but 2205 SS and 304 SS did not suffer from significant weight loss or pitting. Electrochemical tests indicated that 2205 SS was slightly more resistant to SRB MIC than 304 SS, while 410 SS was far less resistant. [ABSTRACT FROM AUTHOR]

Summary: Biocorrosion first surfaced in the scientific literature when Richard H. Gaines associated corrosion with bacterial activities in 1910. It is also known as microbiologically influenced corrosion (MIC). In general, it covers two scenarios. One is that microbes cause corrosion directly, which usually means microbes secrete corrosive metabolites or microbes harvest electrons from a metal for respiration to produce energy. In the second scenario, microbes are behind the initiation or acceleration of corrosion caused by a pre‐existing corrosive agent such as water and CO2, by compromising the passive film (often a metal oxide film on a metal). MIC is caused by microbial biofilms. It is everywhere around us. This work dissects some notable examples with perspectives. [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]

Corrosion inhibition by benzalkonium chloride (BKC) against anaerobic CO 2 corrosion and microbiologically influenced corrosion was studied using surface analysis, weight loss and electrochemical measurements. Results showed that the minimal bactericidal concentration of BKC against Desulfotomaculum nigrificans ( D. nigrificans ) was 40 mg L −1 . While at this concentration the planktonic D. nigrificans cell count could recover after 21-day incubation, it resulted in 4 log reduction in sessile D. nigrificans cell count. When 80 mg L −1 BKC was used, both planktonic and sessile D. nigrificans became undetectable. It was found that at these concentrations, BKC reduced both uniform corrosion and pitting corrosion. [ABSTRACT FROM AUTHOR]

The microbiologically influenced corrosion (MIC) resistance of a novel Cu-bearing 2205 duplex stainless steel (2205 Cu-DSS) against an aerobic marinePseudomonas aeruginosabiofilm was investigated. The electrochemical test results showed thatRpincreased andicorrdecreased sharply after long-term immersion in the inoculation medium, suggesting that 2205 Cu-DSS possessed excellent MIC resistance to theP. aeruginosabiofilm. Fluorescence microscope images showed that 2205 Cu-DSS possessed a strong antibacterial ability, and its antibacterial efficiency after one and seven days was 7.75% and 96.92%, respectively. The pit morphology comparison after 14 days between 2205 DSS and 2205 Cu-DSS demonstrated that the latter showed a considerably reduced maximum MIC pit depth compared with the former (1.44 μmvs9.50 μm). The experimental results suggest that inhibition of the biofilm was caused by the copper ions released from the 2205 Cu-DSS, leading to its effective mitigation of MIC byP. aeruginosa. [ABSTRACT FROM AUTHOR]

• Nitrate reducing Pseudomonas aeruginosa corrodes galvanized steel significantly. • The corrosion mechanism is film damage-microbiologically influenced corrosion. • 30 ppm (w/w) trehalase reduces sessile cell count by 0.8-log and weight loss by 14%. • Trehalase enhances 30 ppm THPS with fewer sessile cells and lower weight loss. • This work uses a mini-electrochemical glass cell to minimize chemical consumption. Pseudomonas aeruginosa is a facultative bacterium that is pathogenic. It is ubiquitous in the environment including air handling systems. It causes microbiologically influenced corrosion (MIC) aerobically and anaerobically. In this work, P. aeruginosa was grown as a nitrate reducing bacterium (NRB) in Luria-Bertani medium with KNO 3 at 37 °C. Trehalase, an enzyme which plays a crucial role in biofilm formation was found to enhance the treatment of P. aeruginosa biofilm and its MIC against galvanized steel by tetrakis-hydroxymethyl phosphonium sulfate (THPS) green biocide. After a 7-d incubation, 30 ppm (w/w) trehalase reduced sessile cell count by 0.8-log, and it also reduced galvanized steel weight loss by 14%, compared to 2.3-log and 39%, respectively for the 30 ppm THPS treatment. The combination of 30 ppm THPS + 30 ppm trehalase reduced sessile cell count further by 0.1-log and weight loss by 13% compared to using THPS alone. Electrochemical corrosion measurements supported weight loss results. The injection of 20 ppm riboflavin into a 3-d P. aeruginosa broth failed to accelerate the corrosion rate, suggesting that nitrate reducing P. aeruginosa MIC of galvanized steel did not belong to extracellular electron transfer-MIC, because Zn was hydrolyzed after the microbe damaged the passive film. [ABSTRACT FROM AUTHOR]

Biocorrosion is also known as microbiologically influenced corrosion (MIC). Most anaerobic MIC cases can be classified into two major types. Type I MIC involves non-oxygen oxidants such as sulfate and nitrate that require biocatalysis for their reduction in the cytoplasm of microbes such as sulfate reducing bacteria (SRB) and nitrate reducing bacteria (NRB). This means that the extracellular electrons from the oxidation of metal such as iron must be transported across cell walls into the cytoplasm. Type II MIC involves oxidants such as protons that are secreted by microbes such as acid producing bacteria (APB). The biofilms in this case supply the locally high concentrations of oxidants that are corrosive without biocatalysis. This work describes a mechanistic model that is based on the biocatalytic cathodic sulfate reduction (BCSR) theory. The model utilizes charge transfer and mass transfer concepts to describe the SRB biocorrosion process. The model also includes a mechanism to describe APB attack based on the local acidic pH at a pit bottom. A pitting prediction software package has been created based on the mechanisms. It predicts long-term pitting rates and worst-case scenarios after calibration using SRB short-term pit depth data. Various parameters can be investigated through computer simulation. [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]

Headspace to liquid volumetric ratio can impact bacterial activity, which affects the metabolic process and extracellular electron transportation (EET) of microbial biofilms. In this work, the ratio of headspace volume to culture medium volume was varied to investigate the behavior of Cu microbiologically influenced corrosion (MIC) by P. aeruginosa as a nitrate reducing bacterium (NRB). This NRB produced ammonia as a toxic metabolite that inhibited its growth in anaerobic bottles. The results showed that a larger headspace volume led to lower ammonium concentration in the liquid phase (due to escape of ammonia to the headspace), higher planktonic and sessile cell counts, deeper pits and higher uniform corrosion rate. With a fixed culture medium volume of 200 mL, the weight loss of Cu coupons corresponding to 500 mL and 200 mL headspace volumes were approximately 1.9-fold and 1.5-fold larger than that for 50 mL headspace volume, respectively, with corresponding pit depth increased by 2.6 times and 1.7 times, respectively. Ammonia acted as a complexing agent, not an oxidant (electron acceptor) in the system. The terminal electron acceptor was nitrate. The reduction of nitrate in the cytoplasm of P. aeruginosa using extracellular electrons released by Cu oxidation is thermodynamically favorable. Thus, Cu corrosion by the nitrate reducing P. aeruginosa biofilm belongs to EET-MIC. • Nitrate reduction coupled with Cu oxidation is thermodynamically favorable. • NH 4 + in P. aeruginosa broth inhibits sessile cell growth and thus impacts MIC. • Increased headspace leads to higher sessile cell count and more severe Cu MIC. • Localized corrosion and general corrosion are observed in 14-day tests. • Data support the mechanism for Cu MIC with electron uptake by the nitrate reducer. [ABSTRACT FROM AUTHOR]

Oceanic facilities and equipment corrosion present considerable economic and safety concerns, predominantly due to microbial corrosion. Early detection of corrosive microbes is pivotal for effective monitoring and prevention. Yet, traditional detection methods often lack specificity, require extensive processing time, and yield inaccurate results. Hence, the need for an efficient real-time corrosive microbe monitoring technology is evident. Pseudomonas aeruginosa , a widely distributed microorganism in aquatic environments, utilizes its production of quinone-like compounds, specifically pyocyanin (PYO), to corrode metals. Here, we report a novel fiber optic surface plasmon resonance (SPR) sensor modified by the C-terminal of BrlR protein (BrlR-C), which is a specific receptor of PYO molecule, to detect P. aeruginosa in aquatic environments. The results showed that the sensor had a good ability to recognize PYO in the concentration range of 0–1 μg/mL, and showed excellent sensing performance in real-time monitoring the growth status of P. aeruginosa. With a strong selectivity of PYO, the sensor could clearly detect P. aeruginosa against other bacteria in seawater environment, and exhibited excellent anti-interference ability against variations in pH, temperature and pressure and other interfering substances. This study provides a useful tool for monitoring corrosive P. aeruginosa biofilm in aquatic environments, which is a first of its kind example that serves as a laboratory model for the application of fiber optic technology in real-world scenarios to monitoring biofilms in microbial corrosion and biofouling. [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]

The microbiologically influenced corrosion (MIC) of copper via extracellular electron transfer (EET) caused by Halomonas titanicae was investigated using two different methods. Copper corrosion in enriched seawater was accelerated by H. titanicae and was further promoted by riboflavin (RF), an electron mediator that can accelerate EET. Within minutes of 20 ppm RF injection, the copper corrosion started to increase. The copper weight loss for 100% carbon source reduction was 1.4 times that of 0% carbon source reduction. The RF injection data together with carbon starvation data indicate that H. titanicae utilized elemental copper as an electron source to cause EET-MIC. [Display omitted] • Nitrate reducing H. titanicae can utilize rather noble copper as an electron donor. • Copper MIC rate starts to increase within minutes after riboflavin injection. • Riboflavin can be used as a probe to confirm EET-MIC by nitrate reducing bacteria. [ABSTRACT FROM AUTHOR]

Bifunctional antibacterial and anticorrosive broad-spectrum rosin thiourea iminazole quaternary ammonium salt (RTIQAS) was investigated to inhibit microbiologically influenced corrosion (MIC) caused by anaerobic gram-negative sulfate reducing bacterium (SRB) Desulfovibrio vulgaris against X80 carbon steel and aerobic gram-positive bacterium Bacillus licheniformis against 316L stainless steel. It also indicated that RTIQAS was more effective than common commercial biocides THPS (tetrakis hydroxymethyl phosphonium sulfate) and glutaraldehyde at the same concentration against X80 carbon steel corrosion by D. vulgaris. In the molecular simulation, the interaction energy confirmed the favorable adsorption of RTIQAS on the metal surfaces, indicating its potential as an effective corrosion inhibitor. • A bifunctional antibacterial and anticorrosive inhibitor RTIQAS was synthesized. • RTIQAS had antibacterial performances against anaerobic Desulfovibrio vulgaris on X80 carbon steel. • RTIQAS presented antibacterial abilities against aerobic Bacillus licheniformis on 316 L stainless steel. • RTIQAS showed better inhibition effect than two common commercial biocides against D. vulgaris. • RTIQAS molecules were adsorbed on iron surface based on molecular [ABSTRACT FROM AUTHOR]

Sulfate-reducing bacterium Desulfovibrio vulgaris promoted the microbiologically influenced corrosion (MIC) of CoCrFeMnNi high entropy alloy (HEA) and led to pitting corrosion. D. vulgaris caused the formation of metal sulfides and thinning of passive film. The corrosion resistance decreased, and pit depths increased when the carbon source reduced to 40%. The relative expression of hydrogenase genes hydA and hydB in the biofilms under 40% carbon source significantly increased, indicating that the indirect electron transfer mediated by 2H+/H 2 might play an important role in promoting the HEA MIC by D. vulgaris under starvation. • Desulfovibrio vulgaris promotes CoCrFeMnNi HEA MIC and causes pitting corrosion. • The presence of D. vulgaris causes the thinning of HEA passive film. • In the starved 40% carbon source level, D. vulgaris leads to more aggressive HEA MIC. • Two hydrogenase genes (hydA and hydB) upregulate in the starvation condition. • The indirect electron transfer mediated by 2H+/H 2 may play an important role in starvation. [ABSTRACT FROM AUTHOR]

The mitigation of microbiologically influenced corrosion (MIC) of 304L stainless steel (SS) against Pseudomonas aeruginosa by a Salvia officinalis extract was investigated using electrochemical and surface analysis techniques. The extract was characterized by HPLC-Q-TOF-MS and its antibiofilm property was evaluated. The data revealed the presence of well-known antimicrobial and anticorrosion compounds in the extract. The S. officinalis extract was found effective in preventing biofilm formation and inhibiting mature biofilm. Electrochemical results indicated that P. aeruginosa accelerated the MIC of 304L SS, while the extract was found to prevent the MIC with an inhibition efficiency of 97.5 ± 1.5%. This was attributed to the formation of a protective film by the adsorption of some compounds from the extract on the 304L SS surface. Unlabelled Image • Pseudomonas aeruginosa biofilm accelerates the corrosion of 304L stainless steel. • Salvia officinalis extract effectively prevents the P. aeruginosa biofilm formation. • S. officinalis extract successfully removes the mature P. aeruginosa biofilm. • S. officinalis compounds adsorb on the 304L SS and form a protective layer. • Experimental data confirm the MIC mitigation by the extract. [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]

Abstract A biocide enhancer is a chemical that can enhance the efficacy of a biocide or reduce its dosage. In this work, a novel peptide was tested as a biocide enhancer. A chemically synthesized 14-mer peptide (Peptide A), which was found non-biocidal, has an amino acid sequence derived from sea anemone Actinia equina that possesses a biofilm-free exterior. Peptide A at 180 ppb (w/w) or 100 nM enhanced 100 ppm tetrakis hydroxymethyl phosphonium sulfate (THPS) against an oilfield biofilm consortium grown on C1018 carbon steel in an enriched artificial seawater medium. The combination of 100 nM Peptide A + 100 ppm THPS led to additional 2-log reduction, 1-log reduction, 1-log reduction in sessile sulfate reducing bacteria (SRB) cell count, sessile acid producing bacteria (APB) cell count, and sessile general heterotrophic bacteria (GHB) cell count, in comparison with the treatment using 100 ppm THPS alone in a 14-day laboratory biofilm prevention test. The data in this work suggest that non-biocidal Peptide A is a promising biocide enhancer that should be further explored. Graphical abstract Image 1 Highlights • Cyclic Peptide A is engineered based on a 12-mer sequence in Equinatoxin II protein. • Peptide A reduces tetrakis (hydroxymethyl) phosphonium sulfate (THPS) dosage. • Peptide A at ppb levels enhances the biocide against an oilfield biofilm consortium. • The biocide cocktail reduces carbon steel weight loss and maximum pit depth. • Linear polarization resistance results corroborate weight loss and pitting data. [ABSTRACT FROM AUTHOR]

Abstract In nature, microbes tend to form synergistic biofilms on a wide range of materials using extracellular polymeric substances to embed sessile cells. Problematic biofilms provide environments conducive to the occurrence of microbiologically influenced corrosion (MIC) in many industries. MIC includes corrosion caused by microbes as well as corrosion by another pre-existing corrosion agent that is accelerated by microbes. There are several distinct types of MIC mechanisms associated with different microbial species and metabolism types. Biofilms employ different defense mechanisms to protect themselves from environmental hazards. This makes sessile cells in biofilms much more resistant to treatment than planktonic cells. Biofilms are often treated with biocides together with physical scrubbing. Various approaches have been developed to boost biocide efficacy. New emerging technologies such as bacterial phages, quorum sensing inhibitors, and special chemicals to enhance biocides have been proposed in recent years. This review evaluates these different treatment methods and various techniques used to assess biocide treatment outcome including microbiology, molecular biology, corrosion testing and electrochemical methods. Highlights • Biofilms cause microbiologically influenced corrosion (MIC) and biofouling. • Some microorganisms cause MIC via extracellular electron transfer to get energy. • Some microorganisms secrete corrosive metabolites that lead to MIC. • Biocide enhancers and other new technologies help mitigate biofilms. • Electrochemical methods can be used to study MIC and to assess biocide efficacy. [ABSTRACT FROM AUTHOR]

In this work, microbial corrosion behavior of Ti-6Al-4V (TC4) alloy caused by electroactive Desulfovibrio ferrophilu s biofilm in enriched artificial seawater containing soluble electron shuttle was investigated. The addition of riboflavin-shuttle did not significantly change the planktonic and sessile cell counts but accelerated the microbiologically influenced corrosion of TC4 alloy. The Hilbert-Huang transform revealed the evolution of corrosion pits and the maximum pit depth enhanced with the increase of electron shuttle concentration. Electrochemical measurements proved that riboflavin-shuttle decreased the shuttled electron barrier and increased the anodic dissolution rate. Phase, organization and grain size of alloy were influenced by the MIC. • Ti-6Al-4 V (TC4) is not immune to Desulfovibrio ferrophilus. • Electron shuttle advances the transition of TC4 corrosion pits from metastable to stable state. • Rapid response of D. ferrophilus biofilms to riboflavin shuttle injection. • SRB-MIC decreases the α phase of the alloy. [ABSTRACT FROM AUTHOR]

In industrial and clinical settings, microbiologically influenced corrosion (MIC), also known as biocorrosion, is a major problem associated with materials degradation and infection. To mitigate biofilms, a Cu-bearing 2205 duplex stainless steel (2205-Cu DSS) was created by researchers to utilize the antimicrobial ability of copper. In this study, nitrate reducing Pseudomonas aeruginosa biofilm was grown as a nitrate reducing bacterium to investigate the antimicrobial efficacy and the MIC inhibition efficacy of 2205-Cu DSS under anaerobic condition. The results showed that both biofilm sessile cell count and electrochemically-measured corrosion rate were reduced compared with the 2205 duplex stainless steel (2205 DSS) control. [ABSTRACT FROM AUTHOR]

Microbiologically influenced corrosion (MIC) in the marine environment is a serious threat to the service life of marine materials. MIC pitting corrosion rate is usually much faster than the general corrosion process. The 2304 duplex stainless steel (DSS) is an excellent alternative to 316L SS in marine applications, while its MIC behavior is barely known. In this work, surface analysis and electrochemical techniques were used to study the corrosion behavior of 2304 DSS caused by the ubiquitous marine aerobe Pseudomonas aeruginosa . Compared with the abiotic control, the largest pit depth showed that the P. aeruginosa biofilm greatly accelerated the pitting corrosion (11.0 μm vs. 4.8 μm for the abiotic control). The presence of P. aeruginosa biofilm oxidized the passive film of 2304 DSS from Cr 2 O 3 to CrO 3 , which was a water-soluble compound, resulting in the decrease of the relative Cr content and destruction of the passive film. The linear polarization resistance (LPR), electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS) and polarization curve analyses all demonstrated that 2304 DSS was susceptible to MIC. [ABSTRACT FROM AUTHOR]

Microbiologically influenced corrosion (MIC) is prevalent in the oil and gas industry. Problematic biofilms cause MIC and reservoir souring. A high biocide concentration is usually required to mitigate biofilms compared with planktonic cells. This causes economic and environmental concerns. A biocide enhancer can make a biocide more effective using the same or lower biocide dosage. In this work, an equimolar mixture of 100 ppm (w/w) of four D-amino acids (D-methionine, D-tyrosine, D-tryptophan, and D-leucine) labeled as D-mix enhanced 100 ppm tetrakis (hydroxymethyl) phosphonium sulfate (THPS) against a field biofilm consortium on C1018 carbon steel coupons. In order to test chemical compatibilities, D-amino acids were added together with THPS and enhanced oil recovery chemicals (a polymer, a surfactant, a corrosion inhibitor, and a scale inhibitor) to treat the mature biofilm consortium. After a 7-day biofilm removal test in 125 ml anaerobic vials, the cocktail of 100 ppm THPS +100 ppm D-mix achieved extra logs of reduction in sessile cell counts compared with the 100 ppm THPS alone treatment. The combination also achieved lower weight loss and smaller maximum pit depths. Electrochemical tests corroborated the weight loss and pitting 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]

• Stainless steel alloying elements impact SRB sessile cell count considerably. • A lower PREN leads to more severe passive film damage and SRB corrosion. • MIC severity after 14-day incubation is 2205 SS < 316L SS < 304 SS < 410 SS. • 410 SS has the lowest PREN, highest sessile cell count, and most severe MIC. • 410 SS has 0.75 ± 0.12 mg/cm2 weight loss and 35 μm pit depth after 14 days. Stainless steels (SS) are not immune to microbiologically influenced corrosion (MIC) especially in the presence of sulfate reducing bacteria (SRB). It is necessary to study the influence of alloying elements on the MIC. SRB MIC behaviors of four stainless steels (2205 SS, 316L SS, 304 SS, and 410 SS), with different alloying element compositions were compared after 14 days of incubation at 37°C in enriched artificial seawater inoculated with Desulfovibrio sp. The sessile cell sequence was 410 SS > 316L SS > 304 SS > 2205 SS, inversely proportional to Cr content. The uniform corrosion rate (based on weight loss) sequence was 410 SS > 304 SS > 316L SS > 2205 SS, which matches the pitting resistance equivalent number (PREN) sequence inversely. 410 SS with the lowest Cr and Mo contents suffered the most severe pitting, with pit depth of 35 μm and weight loss of 0.75 mg/cm2 (0.91 mm/a pitting rate and 25 μm/a uniform corrosion rate). The other three stainless steels with higher Cr and Mo contents suffered only metastable pits. The semiconductor characteristics and the re-passivation abilities of the passive films were found to be affected by Cr and Mo contents. [ABSTRACT FROM AUTHOR]

• Ti is not completely immune to SRB (sulfate reducing bacteria) corrosion. • Carbon source starvation and riboflavin both accelerate Ti MIC by D. vulgaris. • Various electrochemical tests confirm increased Ti MIC under SRB starvation. • SRB MIC of Ti mechanism is extracellular electron transfer-MIC (EET-MIC) • Ti MIC pit depth of up to 6.2 µm is observed after 14 d SRB incubation. Desulfovibrio vulgaris biofilm was pre-grown on Ti coupons for 7 d and then the biofilm covered coupons were incubated again with fresh culture media with 10 % (reduced) and 100 % (normal) carbon source levels, respectively. After the pre-growth, sessile D. vulgaris cell count reached 107 cells/cm2. The sessile cell counts were 2 × 107 and 4.2 × 107 cells/cm2 for 10 % and 100 % carbon sources, respectively after the subsequent 7 d starvation test. The maximum pit depth after the 7 d pre-growth was 4.7 µm. After the additional 7 d of the starvation test, the maximum pit depth increased to 5.1 µm for 100 % carbon source vs 6.2 µm for 10 % carbon source. Corrosion current density (i corr) from potentiodynamic polarization data at the end of the 7 d starvation test for 10 % carbon source was more than 3 times of that for 100 % carbon source, despite a reduced sessile cell count with 10 % carbon source. The polarization resistance (R p) started to decrease within minutes after 20 ppm (w/w) riboflavin (electron mediator) injection. The carbon starvation data and riboflavin corrosion acceleration data both suggested that D. vulgaris utilized elemental Ti as an electron source to replace carbon source as the electron donor during carbon source starvation. [ABSTRACT FROM AUTHOR]

Carbon steel microbiologically influenced corrosion (MIC) by sulfate reducing Desulfovibrio vulgaris belongs to extracellular electron transfer MIC (EET-MIC). Adding 20 ppm (w/w) Fe 3 O 4 magnetite nanoparticles (MNPs) to ATCC 1249 culture medium did not alter sessile and planktonic cell counts significantly, but it caused 59% more weight loss and 85% deeper pit depth, respectively after 7 days of incubation. Electrochemical data corroborated the increases. In comparison, D. vulgaris MIC of Cu was not affected by 20 ppm MNPs because it belongs to metabolite MIC (M-MIC) without EET. Thus, MNPs can be a useful tool to distinguish some EET-MIC cases from M-MIC. • Magnetite nanoparticles (MNPs) accelerate extracellular electron transfer (EET). • 20 ppm (w/w) MNPs accelerate EET-MIC of carbon steel by D. vulgaris. • 59% and 85% increases in weight loss and pit depth, respectively are observed. • Magnetism helps to attract MNPs to a carbon steel coupon surface. • Insoluble MNPs can be a useful tool to distinguish EET-MIC from metabolite-MIC. [ABSTRACT FROM AUTHOR]

• S. oneidensis forms thick biofilms (∼50 µm) on SS coupons under aerobic condition. • Flavins can not be used as intermediary electron carriers for SS. • Strain ∆ mtrCBA corrodes SS substantially less than wild-type in aerobic cultures. • Strain ∆ mtrCBA does not reduce nitrate only with SS under anaerobic condition. • Direct electron uptake is a mechanism for SS corrosion in aerobic environments. Shewanella oneidensis MR-1 is an attractive model microbe for elucidating the biofilm-metal interactions that contribute to the billions of dollars in corrosion damage to industrial applications each year. Multiple mechanisms for S. oneidensis -enhanced corrosion have been proposed, but none of these mechanisms have previously been rigorously investigated with methods that rule out alternative routes for electron transfer. We found that S. oneidensis grown under aerobic conditions formed thick biofilms (∼50 µm) on stainless steel coupons, accelerating corrosion over sterile controls. H 2 and flavins were ruled out as intermediary electron carriers because stainless steel did not reduce riboflavin and previous studies have demonstrated stainless does not generate H 2. Strain ∆ mtrCBA , in which the genes for the most abundant porin-cytochrome conduit in S. oneidensis were deleted, corroded stainless steel substantially less than wild-type in aerobic cultures. Wild-type biofilms readily reduced nitrate with stainless steel as the sole electron donor under anaerobic conditions, but strain ∆ mtrCBA did not. These results demonstrate that S. oneidensis can directly consume electrons from iron-containing metals and illustrate how direct metal-to-microbe electron transfer can be an important route for corrosion, even in aerobic environments. [Display omitted] [ABSTRACT FROM AUTHOR]