The role of biofilms in the corrosion of steel in marine environments

Experimental and Theoretical Investigation of the Inhibitor Efficiency of Eucalyptus globulus Leaf Essential Oil (EuEO) on Mild Steel Corrosion in a Molar Hydrochloric Acid Medium

As a corrosion inhibitor for mild steel in a molar hydrochloric acid medium, we investigated the potential of Eucalyptus globulus essential oil (EuEO). Through electrochemical impedance spectroscopy (EIS), potentiodynamic polarization curves, and theoretical methods, including DFT/B3LYP 6-31G (d, p) and Monte Carlo simulations, the interactions between the EuEO components and the steel surface were analyzed. D-Allose, Betulinaldehyde, and Uvaol were identified as the major active compounds in the GC-MS analysis. The experimental results showed that EuEO reached an inhibitory efficiency as high as 97% at a 1 g/L concentration. The findings suggest that EuEO operates as a mixed-type inhibitor, reducing both cathodic and anodic reactions, as well as building up a protective coating on the steel surface. Simulations also confirmed that EuEO molecules function as electron donors and acceptors, enhancing corrosion resistance.

Increased secretion of bacterial pyomelanin caused by light accelerates corrosion of low alloy steel

Microorganisms in the waterline zone can secrete pigments to avoid damage caused by ultraviolet radiation, some of which have corrosive effects. In this work, we found that the secretion of pyomelanin by P3 strain of Pseudoalteromonas lipolytica significantly increases under strong lighting conditions, accelerating the corrosion of the material. Molecular mechanisms indicate that strong light, as a stressful environmental factor, enhances the expression of melanin secretion-related genes to prevent bacteria from being damaged by ultraviolet radiation. Therefore, this work proposes a new corrosion mechanism in the waterline zone, pigment-producing microorganisms are also involved in the waterline corrosion process.

In-situ and label-free measurement of cytochrome C concentration with a Ti2C-MXene sensitized fiber-optic MZI sensor

BACKGROUND

The concentration of cytochrome C is demonstrated to be an effective indicator of the microbial corrosion strength of metals. Traditional cytochrome C sensor can detect cytochrome C with a low detection limit, but their use is limited by their high cost, cumbersome operation, and susceptibility to malignant environments. In addition, studies on the monitoring of cytochrome C in the field of microbial corrosion has still not been carried out. Therefore, there is a need for a highly sensitive, selective, low-cost, anti-interference, and stable cytochrome C sensor with online monitoring and remote sensing capabilities for in-situ measurement of microbial corrosion strength.

RESULTS

This paper proposed a highly sensitive label-free fiber-optic sensor based on Mach-Zehnder interferometer (MZI) for in-situ measurement of the microbial corrosion marker cytochrome C. Two-dimensional Ti2C-MXene material is uniformly immobilized onto the surface of the sensing area to improve the sensitivity, hydrophilicity, and specific surface area of the sensing area, as well as to facilitate the immobilization of specific sensitive materials. The cytochrome C antibody is modified on the surface of Ti2C-MXene to specifically recognize cytochrome C, whose concentration variation can be measured by monitoring the spectral shift of MZI sensor. Results demonstrate a measurement sensitivity of 1.428 nm/μM for cytochrome C concentrations ranging from 0 to 7.04 μM. The detection limit of the sensor is calculated to be 0.392 μM with remarkable performance, including selectivity, stability, and reliability. Besides, the measurement result of the proposed sensor in real microbial corrosive environment is consistent with that of the ideal environment.

SIGNIFICANCE AND NOVELTY

This is the first instance of achieving in-situ and label-free measurement of cytochrome C by using a fiber-optic MZI sensor, which undoubtedly provides a feasible solution for the effective monitoring of microbial metal corrosion in the environment.

Genome-Wide Computational Prediction and Analysis of Noncoding RNAs in Oleidesulfovibrio alaskensis G20

Noncoding RNAs (ncRNAs) play key roles in the regulation of important pathways, including cellular growth, stress management, signaling, and biofilm formation. Sulfate-reducing bacteria (SRB) contribute to huge economic losses causing microbial-induced corrosion through biofilms on metal surfaces. To effectively combat the challenges posed by SRB, it is essential to understand their molecular mechanisms of biofilm formation. This study aimed to identify ncRNAs in the genome of a model SRB, Oleidesulfovibrio alaskensis G20 (OA G20). Three in silico approaches revealed genome-wide distribution of 37 ncRNAs excluding tRNAs in the OA G20. These ncRNAs belonged to 18 different Rfam families. This study identified riboswitches, sRNAs, RNP, and SRP. The analysis revealed that these ncRNAs could play key roles in the regulation of several pathways of biosynthesis and transport involved in biofilm formation by OA G20. Three sRNAs, Pseudomonas P10, Hammerhead type II, and sX4, which were found in OA G20, are rare and their roles have not been determined in SRB. These results suggest that applying various computational methods could enrich the results and lead to the discovery of additional novel ncRNAs, which could lead to understanding the "rules of life of OA G20" during biofilm formation.

Nanocomposites against Pseudomonas aeruginosa biofilms: Recent advances, challenges, and future prospects

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that causes life-threatening and persistent infections in immunocompromised patients. It is the culprit behind a variety of hospital-acquired infections owing to its multiple tolerance mechanisms against antibiotics and disinfectants. Biofilms are sessile microbial aggregates that are formed as a result of the cooperation and competition between microbial cells encased in a self-produced matrix comprised of extracellular polymeric constituents that trigger surface adhesion and microbial aggregation. Bacteria in biofilms exhibit unique features that are quite different from planktonic bacteria, such as high resistance to antibacterial agents and host immunity. Biofilms of P. aeruginosa are difficult to eradicate due to intrinsic, acquired, and adaptive resistance mechanisms. Consequently, innovative approaches to combat biofilms are the focus of the current research. Nanocomposites, composed of two or more different types of nanoparticles, have diverse therapeutic applications owing to their unique physicochemical properties. They are emerging multifunctional nanoformulations that combine the desired features of the different elements to obtain the highest functionality. This review assesses the recent advances of nanocomposites, including metal-, metal oxide-, polymer-, carbon-, hydrogel/cryogel-, and metal organic framework-based nanocomposites for the eradication of P. aeruginosa biofilms. The characteristics and virulence mechanisms of P. aeruginosa biofilms, as well as their devastating impact and economic burden are discussed. Future research addressing the potential use of nanocomposites as innovative anti-biofilm agents is emphasized. Utilization of nanocomposites safely and effectively should be further strengthened to confirm the safety aspects of their application.

Biofouling and corrosion rate of welded Nickel Aluminium Bronze in natural and simulated seawater

Updated understanding on the effect of biofouling on corrosion rate is needed to protect marine structures as climate change is altering seawater physiochemistry and biofouling organism distribution. Multi-disciplinary techniques can improve understanding of biofouling development and associated corrosion rates on metals immersed in natural seawater (NSW). In this study, the development of biofouling and corrosion on welded Nickel Aluminium Bronze (NAB) was investigated through long-term immersion tests in NSW, simulated seawater (SSW) and air. Biofouling was affected by geographic location within the marina and influenced corrosion extent. The corrosion rate of NAB was accelerated in the initial months of exposure in NSW (1.27 mm.yr-1) and then settled to 0.11 mm.yr-1 (annual average). This was significantly higher than the 0.06 mm.yr-1 corrosion rate measured in SSW, which matched published rates. The results suggest that corrosion rates for cast NAB should be revised to take account of biofouling and updated seawater physiochemistry.

Intelligent analysis of corrosion characteristics of steel pipe piles of offshore construction wharfs based on computer vision

The lower part of offshore construction wharfs is mostly a steel structure system composed of steel pipe piles, whose corrosion level directly affects the structural safety performance of steel wharfs in service. The currently common corrosion detection methods can only sample and inspect steel pile after it has been dismantled, making it impractical for in-service monitoring during the operational period of the steel pile. In this paper, a deep learning-based image classification model is first established to recognize the type of corroded area on steel pipe piles. The model achieves a recognition accuracy of 99.14 % in automatically identifying different types of corroded areas, including full immersion zone, tidal range zone, and splash zone. Subsequently, digital image processing technology is utilized to automatically calculate the corroded area of steel pipe piles. The method proposed in this paper can obtain the key information, such as type of corrosion area and area of the steel pipe pile corrosion area, without damaging their structural performance during the service. With this data, the mechanical performance of steel pipe piles can be analyzed, and the structural safety of the in-service steel pipe piles can be determined, thereby ensuring the safety of the construction wharf.

PlzD modifies Vibrio vulnificus foraging behavior and virulence in response to elevated c-di-GMP

IMPORTANCE

Many free-swimming bacteria propel themselves through liquid using rotary flagella, and mounting evidence suggests that the inhibition of flagellar rotation initiates biofilm formation, a sessile lifestyle that is a nearly universal surface colonization paradigm in bacteria. In general, motility and biofilm formation are inversely regulated by the intracellular second messenger bis-(3´-5´)-cyclic dimeric guanosine monophosphate (c-di-GMP). Here, we identify a protein, PlzD, bearing a conserved c-di-GMP binding PilZ domain that localizes to the flagellar pole in a c-di-GMP-dependent manner and alters the foraging behavior, biofilm, and virulence characteristics of the opportunistic human pathogen, Vibrio vulnificus. Our data suggest that PlzD interacts with components of the flagellar stator to decrease bacterial swimming speed and changes in swimming direction, and these activities are enhanced when cellular c-di-GMP levels are elevated. These results reveal a physical link between a second messenger (c-di-GMP) and an effector (PlzD) that promotes transition from a motile to a sessile state in V. vulnificus.

Substrate Specificity of Biofilms Proximate to Historic Shipwrecks

The number of built structures on the seabed, such as shipwrecks, energy platforms, and pipelines, is increasing in coastal and offshore regions. These structures, typically composed of steel or wood, are substrates for microbial attachment and biofilm formation. The success of biofilm growth depends on substrate characteristics and local environmental conditions, though it is unclear which feature is dominant in shaping biofilm microbiomes. The goal of this study was to understand the substrate- and site-specific impacts of built structures on short-term biofilm composition and functional potential. Seafloor experiments were conducted wherein steel and wood surfaces were deployed for four months at distances extending up to 115 m away from three historic (>50 years old) shipwrecks in the Gulf of Mexico. DNA from biofilms on the steel and wood was extracted, and metagenomes were sequenced on an Illumina NextSeq. A bioinformatics analysis revealed that the taxonomic composition was significantly different between substrates and sites, with substrate being the primary determining factor. Regardless of site, the steel biofilms had a higher abundance of genes related to biofilm formation, and sulfur, iron, and nitrogen cycling, while the wood biofilms showed a higher abundance of manganese cycling and methanol oxidation genes. This study demonstrates how substrate composition shapes biofilm microbiomes and suggests that marine biofilms may contribute to nutrient cycling at depth. Analyzing the marine biofilm microbiome provides insight into the ecological impact of anthropogenic structures on the seabed.

Extracellular Electron Transfer in Microbiologically Influenced Corrosion of 201 Stainless Steel by Shewanella algae

The microbiologically influenced corrosion of 201 stainless steel by Shewanella algae was investigated via modulating the concentration of fumarate (electron acceptor) in the medium and constructing mutant strains induced by ΔOmcA. The ICP-MS and electrochemical tests showed that the presence of S. algae enhanced the degradation of the passive film; the lack of an electron acceptor further aggravated the effect and mainly affected the early stage of MIC. The electrochemical tests and atomic force microscopy characterization revealed that the ability of ΔOmcA to transfer electrons to the passive film was significantly reduced in the absence of the c-type cytochrome OmcA related to EET progress, leading to the lower corrosion rate of the steel.

Investigating the Impacts of UVC Radiation on Natural and Cultured Biofilms: An assessment of Cell Viability

Biofilms are conglomerates of cells, water, and extracellular polymeric substances which can lead to various functional and financial setbacks. As a result, there has been a drive towards more environmentally friendly antifouling methods, such as the use of ultraviolet C (UVC) radiation. When applying UVC radiation, it is important to understand how frequency, and thus dose, can influence an established biofilm. This study compares the impacts of varying doses of UVC radiation on both a monocultured biofilm consisting of Navicula incerta and field-developed biofilms. Both biofilms were exposed to doses of UVC radiation ranging from 1626.2 mJ/cm2 to 9757.2 mJ/cm2 and then treated with a live/dead assay. When exposed to UVC radiation, the N. incerta biofilms demonstrated a significant reduction in cell viability compared to the non-exposed samples, but all doses had similar viability results. The field biofilms were highly diverse, containing not only benthic diatoms but also planktonic species which may have led to inconsistencies. Although they are different from each other, these results provide beneficial data. Cultured biofilms provide insight into how diatom cells react to varying doses of UVC radiation, whereas the real-world heterogeneity of field biofilms is useful for determining the dosage needed to effectively prevent a biofilm. Both concepts are important when developing UVC radiation management plans that target established biofilms.

Anaerobic thiosulfate oxidation by the Roseobacter group is prevalent in marine biofilms

Thiosulfate oxidation by microbes has a major impact on global sulfur cycling. Here, we provide evidence that bacteria within various Roseobacter lineages are important for thiosulfate oxidation in marine biofilms. We isolate and sequence the genomes of 54 biofilm-associated Roseobacter strains, finding conserved sox gene clusters for thiosulfate oxidation and plasmids, pointing to a niche-specific lifestyle. Analysis of global ocean metagenomic data suggests that Roseobacter strains are abundant in biofilms and mats on various substrates, including stones, artificial surfaces, plant roots, and hydrothermal vent chimneys. Metatranscriptomic analysis indicates that the majority of active sox genes in biofilms belong to Roseobacter strains. Furthermore, we show that Roseobacter strains can grow and oxidize thiosulfate to sulfate under both aerobic and anaerobic conditions. Transcriptomic and membrane proteomic analyses of biofilms formed by a representative strain indicate that thiosulfate induces sox gene expression and alterations in cell membrane protein composition, and promotes biofilm formation and anaerobic respiration. We propose that bacteria of the Roseobacter group are major thiosulfate-oxidizers in marine biofilms, where anaerobic thiosulfate metabolism is preferred.

Biology and Regulation of Staphylococcal Biofilm

Despite continuing progress in medical and surgical procedures, staphylococci remain the major Gram-positive bacterial pathogens that cause a wide spectrum of diseases, especially in patients requiring the utilization of indwelling catheters and prosthetic devices implanted temporarily or for prolonged periods of time. Within the genus, if Staphylococcus aureus and S. epidermidis are prevalent species responsible for infections, several coagulase-negative species which are normal components of our microflora also constitute opportunistic pathogens that are able to infect patients. In such a clinical context, staphylococci producing biofilms show an increased resistance to antimicrobials and host immune defenses. Although the biochemical composition of the biofilm matrix has been extensively studied, the regulation of biofilm formation and the factors contributing to its stability and release are currently still being discovered. This review presents and discusses the composition and some regulation elements of biofilm development and describes its clinical importance. Finally, we summarize the numerous and various recent studies that address attempts to destroy an already-formed biofilm within the clinical context as a potential therapeutic strategy to avoid the removal of infected implant material, a critical event for patient convenience and health care costs.

A new plate-hanging method for biofilm quantification and its application to evaluate the role of surface hydrophobicity

A novel procedure for the quantitative analysis of biofilm formation by bacteria and yeasts, the Plate-hanging method, was developed. In this system, various polymer disks were hung from the lid of a 6-well plate, immersed in a cell suspension, and moderately shaken (70 rpm). In order to verify the validity of the procedure, the effects of the solid surface hydrophobicity of the test disks and the cell surface hydrophobicities of microorganisms on biofilm formation were investigated. Biofilm formation of bacteria and yeasts on the solid surface strongly depended on hydrophobic interactions between the solid surface and the cell surface. A positive correlation between the hydrophobic properties of substratum and cell surfaces was observed. On the other hand, hydrophilic yeasts preferentially adsorbed onto relatively hydrophilic surfaces. Moreover, the plate-hanging method coupled with the periodic exchange of the liquid medium enabled the quantification of long-term biofilm growth.

Developing an Effective and Durable Film for Marine Fouling Prevention from PDMS/SiO2 and PDMS/PU with SiO2 Composites

Polymer film coating with a highly hydrophobic surface property is a practical approach to prevent fouling of any structures in the marine environment without affecting marine microorganisms. The preparation of a polymer coating, from a simple and easy method of solution blending of hydrophobic polydimethylsiloxane elastomer and hydrophilic polyurethane with SiO₂, was carried out in this study, with the aim of improving characteristics, and the coating demonstrated economic feasibility for antifouling application. Incorporation of SiO₂ particles into PDMS and PDMS/PU polymer film improved mechanical properties of the film and the support fabrication of micropatterns by means of a soft lithography process. Observations from field emission scanning electron microscope (FESEM) of the PDMS/SiO₂ composite film revealed a homogeneous morphology and even dispersion of the SiO₂ disperse phase between 1–5 wt.%. Moreover, the PDMS film with 3 wt.% loading of SiO₂ considerably increased WCA to 115.7° ± 2.5° and improved mechanical properties by increasing Young’s modulus by 128%, compared with neat PDMS film. Additionally, bonding strength between barnacles and the PDMS film with 3 wt.% of SiO₂ loading was 0.16 MPa, which was much lower than the bonding strength between barnacles and the reference carbon steel of 1.16 MPa. When compared to the previous study using PDMS/PU blend (95:5), the count of barnacles of PDMS with 3 wt.% SiO₂ loading was lower by 77% in the two-week field tests and up to 97% in the eight-week field tests. Subsequently, when PDMS with 3 wt.% SiO₂ was further blended with PU, and the surface modified by the soft lithography process, it was found that PDMS/PU (95:5) with 3 wt.% SiO₂ composite film with micropatterns increased WCA to 122.1° ± 2.9° and OCA 90.8 ± 3.6°, suggesting that the PDMS/PU (95:5) with 3 wt.% SiO₂ composite film with surface modified by the soft lithography process could be employed for antifouling application.

Marine biofilms: diversity, interactions and biofouling

Marine biofilms are ubiquitous in the marine environment. These complex microbial communities rapidly respond to environmental changes and encompass hugely diverse microbial structures, functions and metabolisms. Nevertheless, knowledge is limited on the microbial community structures and functions of natural marine biofilms and their influence on global geochemical cycles. Microbial cues, including secondary metabolites and microbial structures, regulate interactions between microorganisms, with their environment and with other benthic organisms, which affects their community succession and metamorphosis. Furthermore, marine biofilms are key mediators of marine biofouling, which greatly affect marine industries. In this Review, we discuss marine biofilm dynamics, including their diversity, abundance and functions. We also highlight knowledge gaps, areas for future research and potential biotechnological applications of marine biofilms.

Accelerating effect of pyocyanin on microbiologically influenced corrosion of 304 stainless steel by the Pseudomonas aeruginosa biofilm

In this study, the influence of exogenous pyocyanin (PYO) on the microbiologically influenced corrosion (MIC) of 304 stainless steel by Pseudomonas aeruginosa was investigated. Under sterile condition, the additional PYO in the culture medium had no effect on the corrosion of 304 stainless steel. In contrast, P. aeruginosa biofilm inoculated in the media with additional PYO resulted in more severe pitting corrosion. EIS and cyclic potentiodynamic polarization results indicated that exogenous PYO promoted the electron transfer efficiency between the P. aeruginosa biofilm and the stainless steel surface. X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM) results further demonstrated that the P. aeruginosa led the breakdown of passive film predominantly by accelerating the bioreductive dissolution of iron oxides.

"Attacking-Attacking" Anti-biofouling Strategy Enabled by Cellulose Nanocrystals-Silver Materials

The development of high-performance anti-biofouling surfaces is paramount for controlling bacterial attachment and biofilm growth in biomedical devices, food packing, and filtration membranes. Cellulose nanocrystals (CNCs), a carbon-nanotube-like nanomaterial, have emerged as renewable and sustainable antimicrobial agents. However, CNCs inactivate bacteria under contact-mediated mechanisms, limiting its antimicrobial property mostly to the attached bacteria. This study describes the combination of CNCs with silver nanoparticles (CNC/Ag) as a strategy to increase their toxicity and anti-biofouling performance. CNC/Ag-coated surfaces inactivated over 99% of the attached Escherichia coli and Bacillus subtilis cells compared to 66.9 and 32.9% reduction shown by the pristine CNC, respectively. CNC/Ag was also very toxic to planktonic cells, displaying minimal inhibitory of 25 and 100 μg/mL against B. subtilis and E. coli, respectively. CNC/Ag seems to inactivate bacteria through an "attacking-attacking" mechanism where CNCs and silver nanoparticles play different roles. CNCs can kill bacteria by piercing the cell membrane. This physical membrane stress-mediated mechanism is demonstrated as lipid vesicles release their encapsulated dye upon contact with CNCs. Once the cell membrane is punctured, silver ions can enter the cell passively and compromise the integrity of DNA and other organelles. Inside the cells, Ag⁺ may damage the cell membrane by selectively interacting with sulfur and nitrogen groups of enzymes and proteins or by harming DNA via accumulation of reactive oxygen species. Therefore, CNC/Ag toxicity seems to combine the puncturing effect of the needle-like CNC and the silver's ability to impair the cell membrane and DNA functionalities.

Gene Sets and Mechanisms of Sulfate-Reducing Bacteria Biofilm Formation and Quorum Sensing With Impact on Corrosion

Sulfate-reducing bacteria (SRB) have a unique ability to respire under anaerobic conditions using sulfate as a terminal electron acceptor, reducing it to hydrogen sulfide. SRB thrives in many natural environments (freshwater sediments and salty marshes), deep subsurface environments (oil wells and hydrothermal vents), and processing facilities in an industrial setting. Owing to their ability to alter the physicochemical properties of underlying metals, SRB can induce fouling, corrosion, and pipeline clogging challenges. Indigenous SRB causes oil souring and associated product loss and, subsequently, the abandonment of impacted oil wells. The sessile cells in biofilms are 1,000 times more resistant to biocides and induce 100-fold greater corrosion than their planktonic counterparts. To effectively combat the challenges posed by SRB, it is essential to understand their molecular mechanisms of biofilm formation and corrosion. Here, we examine the critical genes involved in biofilm formation and microbiologically influenced corrosion and categorize them into various functional categories. The current effort also discusses chemical and biological methods for controlling the SRB biofilms. Finally, we highlight the importance of surface engineering approaches for controlling biofilm formation on underlying metal surfaces.

Characterization of crude oil degrading bacterial communities and their impact on biofilm formation

In the present study, produced water sample collected from the Indian crude oil reservoir is used to enrich the bacterial communities. The impact of these enriched bacterial communities on the biodegradation of crude oil, biofilm formation, and biocorrosion process are elucidated. A crude oil degradation study is carried out with the minimal salt medium and 94% of crude oil was utilized by enriched bacterial communities. During the crude oil degradation many enzymes including alkane hydroxylase, alcohol dehydrogenase, and lipase are playing a key role in the biodegradation processes. The role of enriched bacterial biofilm on biocorrosion reactions are monitored by weight loss studies and electrochemical analysis. Weight loss study revealed that the biotic system has vigorous corrosion attacks compared to the abiotic system. Both AC-Impedance and Tafel analysis confirmed that the nature of the corrosion reaction take place in the biotic system. Very less charge transfer resistance and higher corrosion current are observed in the biotic system than in the abiotic system. Scanning electron microscope confirms that the dense biofilm formation favoured the pitting type of corrosion. X-ray diffraction analysis confirms that the metal oxides formed in the corrosion systems (biotic). From the metagenomic analysis of the V3-V4 region revealed that presence of diverse bacterial communities in the biofilm, and most of them are uncultured/unknown. Among the known genus, Bacillus, Halomonas, etc are dominant in the enriched bacterial biofilm sample. From this study, we conclude that the uncultured bacterial strains are found to be playing a key role in the pitting type of corrosion and they can utilize crude oil hydrocarbons, which make them succeeded in extreme oil reservoir environments.

Analysis of Bacterial Communities on North Sea Macroalgae and Characterization of the Isolated Planctomycetes Adhaeretor mobilis gen. nov., sp. nov., Roseimaritima multifibrata sp. nov., Rosistilla ulvae sp. nov. and Rubripirellula lacrimiformis sp. nov

Planctomycetes are bacteria that were long thought to be unculturable, of low abundance, and therefore neglectable in the environment. This view changed in recent years, after it was shown that members of the phylum Planctomycetes can be abundant in many aquatic environments, e.g., in the epiphytic communities on macroalgae surfaces. Here, we analyzed three different macroalgae from the North Sea and show that Planctomycetes is the most abundant bacterial phylum on the alga Fucus sp., while it represents a minor fraction of the surface-associated bacterial community of Ulva sp. and Laminaria sp. Especially dominant within the phylum Planctomycetes were Blastopirellula sp., followed by Rhodopirellula sp., Rubripirellula sp., as well as other Pirellulaceae and Lacipirellulaceae, but also members of the OM190 lineage. Motivated by the observed abundance, we isolated four novel planctomycetal strains to expand the collection of species available as axenic cultures since access to different strains is a prerequisite to investigate the success of planctomycetes in marine environments. The isolated strains constitute four novel species belonging to one novel and three previously described genera in the order Pirellulales, class Planctomycetia, phylum Planctomycetes.

Influence of Salt Water Flow on Structures and Diversity of Biofilms Grown on 316L Stainless Steel

Salt water, in addition to being a naturally corrosive environment, also includes factors such as temperature, pressure, and the presence of the microbial community in the environment that influence degradation processes on metal surfaces. The presence or absence of water flow over the metal surfaces is also an important aspect that influences the corrosion of metals. The objective of this study was to evaluate the presence or absence of salt water flow in the formation of biofilms grown in 316L stainless steel coupons. For this, the 316L stainless steel coupons were exposed in two different microcosms, the first being a system with continuous salt water flow, and the second without salt water flow system. The results of the sequencing of the 16S rDNA genes showed a clear difference in structures and diversity between the evaluated biofilms. There was greater abundance and diversity in the "In Flux" system when compared to the "No Flux" biofilm. The analysis of bacterial diversity showed a predominance of the Gammaproteobacteria class in both systems. However, at lower taxonomic levels, there were considerable differences in representativeness. Representatives of Vibrionales, Alteromonadales, Oceanospirillales, and Flavobacteriales were predominant in "No Flux", whereas in "In Flux" there was a greater representation of Alteromonadales, Rhodobacterales, and Saprospirales. These findings help to understand how the flow of water influences the dynamics of the formation of microbial biofilms on metal surfaces, which will contribute to the choice of strategies used to mitigate microbial biofouling.

The oil spill and the use of chemical surfactant reduce microbial corrosion on API 5L steel buried in saline soil

In order to evaluate the biocorrosion of API 5L metal buried in saline soils, three different conditions in microcosms were evaluated. The control microcosm contained only saline soil, the second had the addition of petroleum, and the third contained the addition of both petroleum and surfactant. The corrosion rate of the metals was measured by loss of mass after 30 days, and the microbial communities were delineated using 16S rRNA gene sequencing techniques. The species were dominated by halophiles in all samples analyzed. Among the bacteria, the predominant group was Proteobacteria, with emphasis on the Alphaproteobacteria and Gammaproteobacteria. Betaproteobacteria and Deltaproteobacteria members were also identified in a smaller number in all conditions. Firmicutes were especially abundant in the control system, although it was persistently present in other conditions evaluated. Bacteroidetes and Actinobacteria were also present in a considerable number of OTUs in the three microcosms. Halobacteria were predominant among archaea and were present in all conditions. The analysis pointed to a conclusion that in the control microcosm, the corrosion rate was higher, while the microcosm containing only oil had the lowest corrosion rate. These results suggest that, under these conditions, the entry of other carbon sources favors the presence of petroleum degraders, rather than samples involved in the corrosion of metals.

The effects of Methanococcus maripaludis on the corrosion behavior of EH40 steel in seawater

The corrosion behavior of EH40 steel in seawater enriched with Methanococcus maripaludis was investigated through electrochemical methods and surface analysis techniques. The results revealed that the hydrogenotrophic M. maripaludis strain can utilize acetate as an alternative energy source. Corrosion of EH40 steel is initially inhibited, but prolonged exposure with the methanogen leads to an eventual corrosion propagation. During the early stage of immersion in M. maripaludis culture medium, the formation of a protective corrosion products film inhibits EH40 steel corrosion. The presence of M. maripaludis promotes both anodic and cathodic reactions of EH40 steel in the late stage of exposure. Surface analyses revealed that pitting corrosion is closely related to uneven distribution of M. maripaludis biofilm on EH40 steel surface.

Influence of Acidification and Warming of Seawater on Biofouling by Bacteria Grown over API 5L Steel

The acidification and warming of seawater have several impacts on marine organisms, including over microorganisms. The influence of acidification and warming of seawater on biofilms grown on API 5L steel surfaces was evaluated by sequencing the 16S ribosomal gene. For this, three microcosms were designed, the first simulating the natural marine environment (MCC), the second with a decrease in pH from 8.1 to 7.9, and an increase in temperature by 2 °C (MMS), and the third with pH in around 7.7 and an increase in temperature of 4 °C (MES). The results showed that MCC was dominated by the Gammaproteobacteria class, mainly members of the Alteromonadales Order. The second most abundant group was Alphaproteobacteria, with a predominance of Rhodobacterales and Oceanospirillales. In the MMS system there was a balance between representatives of the Gammaproteobacteria and Alphaproteobacteria classes. In MES there was an inversion in the representations of the most prevalent classes previously described in MCC. In this condition, there was a predominance of members of the Alphaproteobacteria Class, in contrast to the decrease in the abundance of Gammaproteobacteria members. These results suggest that possible future climate changes may influence the dynamics of the biofouling process in surface metals.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12088-021-00925-7.

Biochemical and molecular changes of the zosteric acid-treated Escherichia coli biofilm on a mineral surface

Purpose

The main goal of the present work was to assess the effectiveness of zosteric acid (ZA) in hindering Escherichia coli biofilm formation on a mineral surface.

Methods

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) flow system was used to probe in situ the biochemical changes induced by ZA on E. coli sessile cells growing on the zinc selenide ATR plate. Comparative proteome analysis was conducted on the sessile cells to better understand the principal molecular changes that occur on ZA-treated biofilms.

Results

The ZA treatment modified the kinetics of the biofilm development. After the ZA exposure, dramatic changes in the carbohydrates, proteins, and DNA profiles were observed over time in the ATR-FTIR spectra. These results were translated into the physiological effects such as the reduction of both the biomass and the EPS contents, the inhibition of the biofilm growth, and the promotion of the detachment. In E. coli sessile cells, the comparative proteome analysis revealed that, while the stress responses were upregulated, the pathways belonging to the DNA replication and repair were downregulated in the ZA-treated biofilms.

Conclusions

The ZA reduced the binding capability of E. coli cells onto the ZnSe crystal, hindering the firm adhesion and the subsequent biofilm development on a mineral surface. The variation of the protein patterns indicated that the ZA acted as a stress factor on the sessile cells that seemed to discourage biomass proliferation, consequently decreasing the surface colonization.

Bacterial community analysis of biofilm on API 5LX carbon steel in an oil reservoir environment

This study aimed to characterize the biofilm microbial community that causes corrosion of API 5LX carbon steel. API 5LX carbon steel coupons were incubated with raw produced water collected from two oil reservoir stations or filter-sterilized produced water. Biofilm 16S rRNA amplicon sequencing revealed that the bacterial community present in the biofilm was dominated by Proteobacteria, including Marinobacter hydrocarbonoclaustics and Marinobacter alkaliphilus. Electrochemical analysis such as impedance and polarization results indicated that Proteobacteria biofilm accelerated corrosion by ~ twofold (2.1 ± 0.61 mm/years) or ~ fourfold (~ 3.7 ± 0.42 mm/years) when compared to the control treatment (0.95 ± 0.1 mm/years). Scanning electron and atomic force microscopy revealed the presence of a thick biofilm and pitting corrosion. X-ray diffraction revealed higher amounts of the corrosion products Fe₂O₃, γ-FeOOH, and α-FeOOH, and confirmed that the microbial biofilm strongly oxidized the iron and contributed to the acceleration of corrosion of carbon metal API 5LX.

Marine bacterial community analysis on 316L stainless steel coupons by Illumina MiSeq sequencing

In order to evaluate the corrosive action of microorganisms on 316L metal exposed directly to a marine environment, a system was designed to immerse coupons in seawater. After periods of 30, 60 and 90 days, the coupons were recovered, the corrosion rates evaluated and the biofilm samples on their surface were analyzed by 16S rRNA gene sequencing. The results of the corrosion rate showed an acceleration over the entire experimental period. Alpha diversity measurements showed higher rates after 60 days of the experiment, while abundance measurements showed higher rates after 90 days of exposure to the marine environment. The beta-diversity results showed a clear separation between the three conditions and proximity in the indices between replicates of the same experimental condition. The results of 16S rRNA gene sequencing showed that after 30 days of exposure to seawater, there was massive representativeness of the pioneer bacteria, Gamma and Alphaproteobacteria, with emphasis on the genera Alcanivorax, Oceanospirillum and Shewanella. At the 60-day analysis, the Gammaproteobacteria class remained dominant, followed by Alphaproteobacteria and Flavobacteria, and the main representatives were Flexibacter and Pseudoalteromonas. In the last analysis, after 90 days, a change in the described bacterial community profile was observed. The Gammaproteobacteria class was still the largest in diversity and OTUs. The most predominant genera in number of OTUs were Alteromonas, Bacteriovorax and, Nautella. Our results describe a change in the microbial community over coupons directly exposed to the marine environment, suggesting a redirection to the formation of a mature biofilm. The conditions created by the biofilm structure suggest said condition favor biocorrosion on the analyzed coupons.

Changes in microbial community in the presence of oil and chemical dispersant and their effects on the corrosion of API 5L steel coupons in a marine-simulated microcosm

The influence of crude oil and chemical dispersant was evaluated over planktonic bacteria and biofilms grown on API 5L steel surfaces in microcosm systems. Three conditions were simulated, an untreated marine environment and a marine environment with the presence of crude oil and a containing crude oil and chemical dispersant. The results of coupon corrosion rates indicated that in the oil microcosm, there was a high corrosion rate when compared with the other two systems. Analysis of bacterial communities by 16S rRNA gene sequencing described a clear difference between the different treatments. In plankton communities, the Bacilli and Gammaproteobacteria classes were the most present in numbers of operational taxonomic unit (OTUs). The Vibrionales, Oceanospirillales, and Alteromonadales orders were predominant in the treatment with crude oil, whereas in the microcosm containing oil and chemical dispersant, mainly members of Bacillales order were detected. In the communities analyzed from biofilms attached to the coupons, the most preponderant class was Alphaproteobacteria, followed by Gammaproteobacteria. In the control microcosm, there was a prevalence of the orders Rhodobacterales, Aeromonadales, and Alteromonadales, whereas in the dispersed oil and oil systems, the members of the order Rhodobacterales were present in a larger number of OTUs. These results demonstrate how the presence of a chemical dispersant and oil influence the corrosion rate and bacterial community structures present in the water column and biofilms grown on API 5L steel surfaces in a marine environment. KEY POINTS: • Evaluation of the effects of oil and chemical surfactants on the corrosion of API 5L. • Changes in microbial communities do not present corrosive biofilm on API 5L coupons.

Microbial community profiles grown on 1020 carbon steel surfaces in seawater-isolated microcosm

Corrosion of metallic alloys is a concern worldwide, with impacts affecting different production sectors and consequent economic losses in the order of billions of dollars annually. Biocorrosion is a form of corrosion where the participation of microorganisms can induce, accelerate, or inhibit corrosive processes. In this study, it was evaluated that the changes in profile communities, by the sequencing of the 16S ribosomal gene, grown over steel coupons in a microcosm with no additional oxygen supplementation for 120 days. Analysis of abundance and diversity indices indicates marked changes in microbial structures throughout the 120-day period. Homology results of OTUs generated by Illumina sequencing indicated Proteobacteria phylum as the dominant group, comprising about 85.3% of the total OTUs, followed by Firmicutes and Bacteriodetes, both with 7.35%. Analyses at lower taxonomic levels suggested the presence of representatives described as corroders, such as Citreicella thiooxidans, Thalassospira sp., and Limnobacter thiooxidans. In conclusion, the results suggest that no additional oxygen supplementation profoundly altered the core of microbial communities, with a predominance of facultative anaerobic species.

Distinct Profiles in Microbial Diversity on Carbon Steel and Different Welds in Simulated Marine Microcosm

The main studies on the corrosion of metals induced by microorganisms are directed only to the surface of the metal, without considering the presence of welds between these surfaces. For this reason, we evaluated the difference of microbial community grown in carbon steel coupons, and two different types of welds, E7018 and Tungsten electrodes, exposed under simulated microcosm. After 30 days, they were recovered, the biofilms scraped and the microbial communities analyzed by 16S rRNA gene sequencing. The results showed that there was a differentiated distribution among the three samples collected. Proteobacteria phylum composed most of the species described in all samples. At the class level, Gammaproteobacteria was the most detected, followed by Alphaproteobacteria and Flavobacteriia. The most prevalent order was Alteromonadales, which was present in Weld2, followed by Rhodobacteriales, which was more prevalent in Fe1020 and Weld1. The orders Cytophagales, Sphingomonadales, and Burkholderiales were described in higher number in Fe1020, whereas Oceanospirillales, Thiotrichales, Flavobacteriales, Rhodospirillales, and Kordiimonadales were higher in samples Weld1 and Weld2. The analyses between the three evaluated conditions show the presences of bacterial groups preferred by different types of metal, suggesting that approaches in the control of biocorrosion should take into account the chemical composition of the metal.

The effect of magnetic field pretreatment on the corrosion behavior of carbon steel in static seawater

The corrosion behavior of carbon steel pretreated with a magnetic field before electrochemical testing was investigated in static seawater using electrochemical methods in the absence of an external magnetic field. The shift in corrosion potential was more significant with increasing pretreating magnetic field strength, and the corrosion current density also decreased. This implies that the carbon steel corrosion was inhibited. The main reason for this inhibition is that the magnetic field affects the formation of intermediate products on the carbon steel surface by both charge transfer and magnetic ion adsorption. The magnetic field pretreatment will likely offer a new approach for marine anti-corrosion technology.

Effect of magnetic field pretreatment on carbon steel corrosion behavior in seawater was investigated by electrochemical methods. This method can inhibit the corrosion behavior and is expected to provide a new way for marine anti-corrosion.

The era of 'omics' technologies in the study of microbiologically influenced corrosion

Efforts to elucidate the relationships between microorganisms and metal corrosion were mainly directed to understanding the formation of biofilm structures grown on corroded surfaces. The emergence of high throughput DNA sequencing techniques has helped in the description of microbial species involved directly and indirectly in the corrosion processes of alloys. Coupled with sequencing from environmental samples, other methodologies such as metatranscriptome, metaproteomics and metabolomics have allowed a new horizon to be opened on the understanding of the role of corrosive microbial biofilm. Several groups of bacteria and archaea were identified, showing the dominance of Proteobacteria in several samples analyzed and members of groups that previously received less attention, such as Firmicutes and Bacteroidetes. Our research also shows that metagenomic studies describe the presence of various Archaea domain thermophilic and methanogenic groups associated with metal corrosion. Thus, opening the prospect of describing new microbial groups as possible participants in this current global concern.