Accelerated Corrosion of 316L Stainless Steel Caused by Shewanella algae Biofilms

Recent advances in enrichment, isolation, and bio-electrochemical activity evaluation of exoelectrogenic microorganisms

Exoelectrogenic microorganisms (EEMs) catalyzed the conversion of chemical energy to electrical energy via extracellular electron transfer (EET) mechanisms, which underlay diverse bio-electrochemical systems (BES) applications in clean energy development, environment and health monitoring, wearable/implantable devices powering, and sustainable chemicals production, thereby attracting increasing attentions from academic and industrial communities in the recent decades. However, knowledge of EEMs is still in its infancy as only ~100 EEMs of bacteria, archaea, and eukaryotes have been identified, motivating the screening and capture of new EEMs. This review presents a systematic summarization on EEM screening technologies in terms of enrichment, isolation, and bio-electrochemical activity evaluation. We first generalize the distribution characteristics of known EEMs, which provide a basis for EEM screening. Then, we summarize EET mechanisms and the principles underlying various technological approaches to the enrichment, isolation, and bio-electrochemical activity of EEMs, in which a comprehensive analysis of the applicability, accuracy, and efficiency of each technology is reviewed. Finally, we provide a future perspective on EEM screening and bio-electrochemical activity evaluation by focusing on (i) novel EET mechanisms for developing the next-generation EEM screening technologies, and (ii) integration of meta-omics approaches and bioinformatics analyses to explore nonculturable EEMs. This review promotes the development of advanced technologies to capture new EEMs.

Effect of Cu addition to AISI 8630 steel on the resistance to microbial corrosion

Low-alloy, high-strength structural steel AISI 8630 is exposed to severe microbiologically influenced corrosion (MIC) in its application environment. To address this issue, we independently designed and developed an AISI 8630 steel containing 0.4 wt% Cu (Cu-AISI 8630) to exploit the Cu antimicrobial effect. The corrosion behavior of two steels in the presence of marine Pseudomonas aeruginosa biofilm was explored by analyzing weight loss, electrochemical tests, SEM images, corrosion pit dimensions, and corrosion products. The electrochemical test results showed an increase in R_p and a significant positive shift in E_corr for Cu-AISI 8630 steel compared to AISI 8630 steel during the immersion cycles. A comparison of the pit morphology of AISI 8630 steel and Cu-AISI 8630 steel after 14 days showed that the maximum MIC pit depth was significantly reduced in the latter compared to the former (3.65 μm vs 9.47 μm). The XPS results showed that protective Cu₂O and CuO layers were formed on the surface of Cu-AISI 8630 steel. The experimental results show that Cu improves the MIC resistance of Pseudomonas aeruginosa biofilms significantly.

Metagenomics diversity analysis of sulfate-reducing bacteria and their impact on biocorrosion and mitigation approach using an organometallic inhibitor

Sulfate-reducing bacteria (SRB) have impacted the biocorrosion process for various industrial sectors, especially in the oil and gas industry. The higher stability over extreme conditions is the key parameter for their survival in such environments. So far, many materials have been tried to minimize or control the growth of SRB. In the present study, an organo-metallic compound of the zinc sorbate (ZS) was successfully synthesized by the simple co-precipitation method and its improved antibacterial activity against SRB. The SRB consortia are enriched from the sub-surface soil sample and identified by 16s rDNA sequencing by targeting the V3-V4 region. The most dominating genera identified with sulfate-reducing capability are Sulfurospirillum (42 %), Shewanella (19 %) Bacteroides (14 %), and Desulfovibrio (8 %). Further biocorrosion experiments are conducted by weight loss methods. Higher corrosion current density (I_corr) and less charge transfer resistance (R_ct) are observed for the SRB consortia. Concurrently, higher R_ct is kept for the inhibitor-included systems. The slowest release of the sorbate into the medium suppressed the growth of the SRB bacterial cells with 86 ± 3 % corrosion inhibition efficiency and prevented further corrosion reactions by forming a protective layer over the surface of the carbon steel API 5LX. The surface analysis strongly confirmed that SRB caused pitting corrosion, which has been suppressed in the inhibitor-included systems.

Microbiologically influenced corrosion of stainless steel independent of sulfate-reducing bacteria

The presence and activities of microorganisms on metal surfaces can affect corrosion. Microbial communities after such corrosion incidents have been frequently analyzed, but little is known about the dynamics of microbial communities in biofilms on different types of stainless steels, such as austenitic, martensitic, and duplex stainless steels. Here, we conducted immersion experiments on 10 types of stainless steels in a freshwater environment, where microbiologically influenced corrosion was observed. During 22-month of immersion, severe localized corrosions were observed only on martensitic S40300 stainless steel. Microbial community analysis showed notable differences between non-corroded and corroded stainless steels. On the surfaces of non-corroded stainless steels, microbial communities were slowly altered and diversity decreased over time; in particular, relative abundance of Nitrospira sp. notably increased. Whereas microbial communities in corrosion products on corroded stainless steels showed low diversity; in particular, the family Beggiatoaceae bacteria, iron-oxidizing bacteria, and Candidatus Tenderia sp. were enriched. Furthermore, sulfur enrichment during localized corrosion was observed. Since there was no enrichment of sulfate-reducing bacteria, the sulfur enrichment may be derived from the presence of family Beggiatoaceae bacteria with intracellular sulfur inclusion. Our results demonstrated slow and drastic changes in microbial communities on the healthy and corroded metal surfaces, respectively, and microbial communities on the healthy metal surfaces were not affected by the composition of the stainless steel.

Accelerated biocorrosion of stainless steel in marine water via extracellular electron transfer encoding gene phzH of Pseudomonas aeruginosa

Microbiologically influenced corrosion (MIC) constantly occurs in water/wastewater systems, especially in marine water. MIC contributes to billions of dollars in damage to marine industry each year, yet the physiological mechanisms behind this process remain poorly understood. Pseudomonas aeruginosa is a representative marine electro-active bacterium, which has been confirmed to cause severe MIC on carbon steel through extracellular electron transfer (EET). However, little is known about how P. aeruginosa causes corrosion on stainless steel. In this study, the corrosivity of wild-type strain, phzH knockout, phzH complemented, and phzH overexpression P. aeruginosa mutants were evaluated to explore the underlying MIC mechanism. We found the accelerated MIC on 2205 duplex stainless steel (DSS) was due to the secretion of phenazine-1-carboxamide (PCN), which was regulated by the phzH gene. Surface analysis, Mott-Schottky test and H₂O₂ measurement results showed that PCN damaged the passive film by forming H₂O₂ to oxidize chromium oxide to soluble hexavalent chromium, leading to more severe pitting corrosion. The normalized corrosion rate per cell followed the same order as the general corrosion rate obtained under each experimental condition, eliminating the influence of the total amount of sessile cells on corrosion. These findings provide new insight and are meaningful for the investigation of MIC mechanisms on stainless steel. The understanding of MIC can improve the sustainability and resilience of infrastructure, leading to huge environmental and economic benefits.

Direct microbial electron uptake as a mechanism for stainless steel 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. H₂ 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 H₂. 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.

Testing the Test: A Comparative Study of Marine Microbial Corrosion under Laboratory and Field Conditions

Microbially influenced corrosion (MIC) is an aggressive type of corrosion that occurs in aquatic environments and is sparked by the development of a complex biological matrix over a metal surface. In marine environments, MIC is exacerbated by the frequent variability in environmental conditions and the typically high diversity of microbial communities; hence, local and in situ studies are crucial to improve our understanding of biofilm composition, biological interactions among its members, MIC characteristics, and corrosivity. Typically, material performance and anticorrosion strategies are evaluated under controlled laboratory conditions, where natural fluctuations and gradients (e.g., light, temperature, and microbial composition) are not effectively replicated. To determine whether MIC development and material deterioration observed in the laboratory are comparable to those that occur under service conditions (i.e., field conditions), we used two testing setups, in the lab and in the field. Stainless steel (SS) AISI 316L coupons were exposed to southeastern Pacific seawater for 70 days using (i) acrylic tanks in a running seawater laboratory and (ii) an offshore mooring system with experimental frames immersed at two depths (5 and 15 m). Results of electrochemical evaluation, together with those of microbial community analyses and micrographs of formed biofilms, demonstrated that the laboratory setup provides critical information on the early biofilm development process (days), but the information gathered does not predict deterioration or biofouling of SS surfaces exposed to natural conditions in the field. Our results highlight the need to conduct further research efforts to understand how laboratory experiments may better reproduce field conditions where applications are to be deployed, as well as to improve our understanding of the role of eukaryotes and the flux of nutrients and oxygen in marine MIC events.

Development of Antibacterial V/TiO2-Based Galvanic Coatings for Combating Biocorrosion

Recently, TiO₂ crystals have been modified by transition-metal dopants with different physicochemical structures to attain distinguished properties. Considering the similar ionic sizes of V⁴⁺ (0.058 nm) and Ti⁴⁺ (0.061 nm), vanadium in the +4 state can be effectively incorporated into the crystal lattice of TiO₂ to tune the band gap energy by creating an impurity energy level (V⁵⁺/V⁴⁺) below the conduction band (2.1 eV) and retaining the anatase phase. In vanadium-incorporated TiO₂ (V/TiO₂), V⁴⁺ is a good dopant candidate as it can increase the lifetime of the charge carrier and reduce the electron-hole recombination rate, which results in high antibacterial activity under visible light irradiation. The present study explores the V/TiO₂-based hot-dip zinc coating with enhanced electrochemical properties and long-term stability for combating biocorrosion. All the composites and the coatings are characterized by different techniques, including X-ray diffraction, transmission electron microscopy, field emission scanning electron microscopy, energy-dispersive X-ray analysis, confocal laser scanning microscopy, optical surface profilometry, and X-ray photoelectron spectroscopy. The biofilm formation assay and the cell viability assay reveal that the tuned composition of the V/TiO₂-based hot-dip zinc coating effectively kills the adherent bacteria and inhibits biofilm formation on the surface. The high-charge-transfer resistance (225.67, 223.63, and 242.35 Ω cm²) and the high-inhibition efficiency (92.24, 92.30, and 92.02%) of the tuned composition of the V/TiO₂-based hot-dip zinc coating confirm its efficient and sustainable antibiocorrosion performance and long-term stability even after an exposure period of 21 days in different bacterial environments. With the inherent antibacterial properties and antibiocorrosion performance of the developed V/TiO₂-based hot-dip zinc coating, the mild steel substrates can find potential application in different fields, including aquatic and marine environments.