Importance of biofilm formation for corrosion inhibition of SAE 1018 steel by axenic aerobic biofilms

Biofilm modifiers: The disparity in paradigm of oral biofilm ecosystem

A biofilm is a population of sessile microorganisms that has a distinct organized structure and characteristics like channels and projections. Good oral hygiene and reduction in the prevalence of periodontal diseases arise from minimal biofilm accumulation in the mouth, however, studies focusing on modifying the ecology of oral biofilms have not yet been consistently effective. The self-produced matrix of extracellular polymeric substances and greater antibiotic resistance make it difficult to target and eliminate biofilm infections, which lead to serious clinical consequences that are often lethal. Therefore, a better understanding is required to target and modify the ecology of biofilms in order to eradicate the infection, not only in instances of oral disorders but also in terms of nosocomial infections. The review focuses on several biofilm ecology modifiers to prevent biofilm infections, as well as the involvement of biofilm in antibiotic resistance, implants or in-dwelling device contamination, dental caries, and other periodontal disorders. It also discusses recent advances in nanotechnology that may lead to novel strategies for preventing and treating infections caused by biofilms as well as a novel outlook to infection control.

Biodegradation and Characterization of Streptomyces sp. (JMCACA3) from Acid Corroded Iron Plate

From acid corroded iron plates five different types of actinobacteria were isolated. Among the five, JMCACA3 strain was selected for the present study. In ISP media, JMCACA3 strain showed well-developed aerial and substrate mycelia were observed. This strain showed good growth in 12 different carbon and 4 different nitrogen sources. The 16S rRNA sequence of phylogenetic analysis by neighbor-joining method identified the studied strain belongs to Streptomyces sp. The biodegradation activity of the strain analyzed by UV and FTIR analysis, which revealed that the various concentrations of Benzimidazole inhibitor with JMCACA3 culture showed slightly varied results. For weight loss method, mild steel coupons incubated with JMCACA3 culture, Benzimidazole inhibitor + JMCACA3 culture and mixed sample showed that JMCACA3 strain utilized the inhibitor as their energy source and the weight the coupons were slightly varied, evidenced by XRD spectra and showed Fe₂O₃ corrosion products. Our study concluded that the JMCACA3 strain, an iron-reducing actinobacteria which utilizes and converted the corrosion inhibitor Benzimidazole as their energy source. So, it is very urgent to develop more powerful corrosion inhibitor from green biocide or microbial-based biocide and their analog which incorporated into the pre-existing Benzimidazole to increase the corrosion inhibitor level against the biofilm of actinobacterial influenced corrosion.

Beyond Risk: Bacterial Biofilms and Their Regulating Approaches

Bacterial biofilms are complex surface attached communities of bacteria held together by self-produced polymer matrixs mainly composed of polysaccharides, secreted proteins, and extracellular DNAs. Bacterial biofilm formation is a complex process and can be described in five main phases: (i) reversible attachment phase, where bacteria non-specifically attach to surfaces; (ii) irreversible attachment phase, which involves interaction between bacterial cells and a surface using bacterial adhesins such as fimbriae and lipopolysaccharide (LPS); (iii) production of extracellular polymeric substances (EPS) by the resident bacterial cells; (iv) biofilm maturation phase, in which bacterial cells synthesize and release signaling molecules to sense the presence of each other, conducing to the formation of microcolony and maturation of biofilms; and (v) dispersal/detachment phase, where the bacterial cells depart biofilms and comeback to independent planktonic lifestyle. Biofilm formation is detrimental in healthcare, drinking water distribution systems, food, and marine industries, etc. As a result, current studies have been focused toward control and prevention of biofilms. In an effort to get rid of harmful biofilms, various techniques and approaches have been employed that interfere with bacterial attachment, bacterial communication systems (quorum sensing, QS), and biofilm matrixs. Biofilms, however, also offer beneficial roles in a variety of fields including applications in plant protection, bioremediation, wastewater treatment, and corrosion inhibition amongst others. Development of beneficial biofilms can be promoted through manipulation of adhesion surfaces, QS and environmental conditions. This review describes the events involved in bacterial biofilm formation, lists the negative and positive aspects associated with bacterial biofilms, elaborates the main strategies currently used to regulate establishment of harmful bacterial biofilms as well as certain strategies employed to encourage formation of beneficial bacterial biofilms, and highlights the future perspectives of bacterial biofilms.

Fouling Microbial Communities on Plastics Compared with Wood and Steel: Are They Substrate- or Location-Specific?

Although marine biofouling has been widely studied on different substrates, information on biofouling on plastics in the Arabian Gulf is limited. Substrate- and location-specific effects were investigated by comparing the microbial communities developed on polyethylene terephthalate (PET) and polyethylene (PE) with those on steel and wood, at two locations in the Sea of Oman. Total biomass was lower on PET and PE than on steel and wood. PET had the highest bacterial abundance at both locations, whereas chlorophyll a concentrations did not vary between substrates. MiSeq 16S ribosomal RNA sequencing revealed comparable operational taxonomic unit (OTU) richness on all substrates at one location but lower numbers on PET and PE at the other location. Non-metric multidimensional scaling (NMDS) showed distinct clusters of the bacterial communities based on substrate (analysis of similarity (ANOSIM), R = 0.45-0.97, p < 0.03) and location (ANOSIM, R = 0.56, p < 0.0001). The bacterial genera Microcystis and Hydrogenophaga and the diatoms Licmophora and Mastogloia were specifically detected on plastics. Desulfovibrio and Pseudomonas spp. exhibited their highest abundance on steel and Corynebacterium spp. on wood. Scanning electron microscopy (SEM) revealed fissure formation on PET and PE, indicating physical degradation. The presence of free radicals on PET and carbonyl bonds (C=O) on PE, as revealed by Fourier transform infrared (FTIR) spectroscopy, indicated abiotic degradation while hydroxyl groups and spectral peaks for proteins and polysaccharides on PE indicated biotic degradation. We conclude that fouling microbial communities are not only substrate-specific but also location-specific and microbes developing on plastics could potentially contribute to their degradation in the marine environment.

Evaluation of extracellular polymeric substances extracted from waste activated sludge as a renewable corrosion inhibitor

Background

Waste activated sludge (WAS) has recently gained attention as a feedstock for resource recovery. The aim of this study is to investigate the corrosion inhibition efficiencies of extracellular polymeric substances (EPS) extracted from WAS.

Methods

The studied corrosion inhibitors were tested with carbon steel in 3.64% NaCl saturated with CO₂ at 25 °C, which is the typical oilfield environment. They were first prepared by EPS extraction (heating at 80 °C), followed by centrifugation for solid and liquid separation, then the supernatant was freeze-thawed five times for sterilization of microorganisms in WAS to terminate metabolic activities in the test inhibitors to ensure consistency in corrosion inhibition. The EPS mixture (supernatant) was then deemed as the test corrosion inhibitor. The inhibition performance was determined using potentiodynamic polarization scans.

Results

Waste activated sludge alone showed unsatisfactory inhibition. However, EPS extracted from WAS showed an optimum inhibition of approximately 80% with 1,000 mg/L of inhibitor. The average total solid (TS) and EPS contents of the WAS were 7,330 mg TS/L WAS and 110 mg EPS/g TS, respectively. Three sets of extracted EPS were scanned with fourier-transform infrared spectroscopy (FTIR) and showed almost overlapping curves, yielding the consistent inhibition performance.

Discussion

The potentiodynamic polarization results indicated that EPS acts as a mixed-type inhibitor which inhibits corrosion on both anode and cathode sites of metal surfaces. Based on the FTIR results, it was assumed that major chemical groups O–H, N–H, C–N, C=O, and C–H contributed to the inhibition by adsorbing on the metal surface, forming a biofilm that acts as a protective barrier to isolate the metal from its corrosive environment. Results show that WAS EPS corrosion inhibitors have inhibition performance comparable to commercial products, signifying their potential in commercialization. This corrosion inhibitor is renewable, biodegradable, non-toxic, and free from heavy metal, making it a superior green corrosion inhibitor candidate. Additionally, turning biomass into value-added product can be beneficial to the environment and, in this case, deriving new materials from WAS could also transform the economics of wastewater treatment operations.

The influence of Bacillus subtilis on tin-coated copper in an aqueous environment

The influence of Bacillus subtilis (BS) on tin-coated copper in an aqueous environment was investigated by exposing the sample to a culture medium inoculated with BS. Scanning electron microscopy, electrochemical measurements and chemical analyses were performed to study the corrosion mechanism. The experimental results show that BS can adhere and gather on the surface of the sample, resulting in oxygen consumption at the place where the bacteria are densely attached. Increases in the R_ct values after the initial immersion showed that corrosion was inhibited, while decreases in the R_ct values after the later immersion showed that corrosion was accelerated. Our results suggest that differences in oxygen concentration due to activity of BS are the main reason for corrosion of tin-coated copper.

The effect of Bacillus subtilis (BS) on the corrosion behaviour of tin-coated copper was investigated by exposing the sample to a culture medium inoculated with BS.

Anticorrosive influence of Acetobacter aceti biofilms on carbon steel

Microbiologically influenced corrosion (MIC) of carbon steel infrastructure is an emerging environmental and cost issue for the ethanol fuel industry, yet its examination lacks rigorous quantification of microbiological parameters that could reveal effective intervention strategies. To quantitatively characterize the effect of cell concentration on MIC of carbon steel, numbers of bacteria exposed to test coupons were systematically controlled to span four orders of magnitude throughout a seven-day test. The bacterium studied, Acetobacter aceti, has been found in ethanol fuel environments, and can convert ethanol to the corrosive species acetic acid. A. aceti biofilms formed during the test were qualitatively evaluated with fluorescence microscopy, and steel surfaces were characterized by scanning electron microscopy. During exposure, biofilms developed more quickly, and test reactor pH decreased at a faster rate, when cell exposure was higher. Resulting corrosion rates, however, were inversely proportional to cell exposure, indicating that A. aceti biofilms are able to protect carbon steel surfaces from corrosion. This is a novel demonstration of corrosion inhibition by an acid-producing bacterium that occurs naturally in corrosive environments. Mitigation techniques for MIC that harness the power of microbial communities have the potential to be scalable, inexpensive, and green solutions to industrial problems.

Use of organic acids for prevention and removal of Bacillus subtilis biofilms on food contact surfaces

The efficacies of organic acid (citric, malic, and gallic acids) treatments at 1% and 2% concentrations on prevention and removal of Bacillus subtilis biofilms were investigated in this study. The analyses were conducted on microtitration plates and stainless steel coupons. The biofilm removal activities of these organic acids were compared with chlorine on both surfaces. The results showed that citric acid treatments were as powerful as chlorine treatments for prevention and removal of biofilms. The antibiofilm effects of malic acid treatments were higher than gallic acid and less than citric acid treatment. When the antibiofilm effects of these acids and chlorine on the two surfaces were compared, the prevention and removal of biofilms were measured higher on microtitration plates than those on stainless steel coupons. Higher reductions were obtained by increasing concentrations of sanitizers on 24-hour biofilm with 20-minute sanitizer treatments for removal of biofilms.

The dual role of microbes in corrosion

Corrosion is the result of a series of chemical, physical and (micro) biological processes leading to the deterioration of materials such as steel and stone. It is a world-wide problem with great societal and economic consequences. Current corrosion control strategies based on chemically produced products are under increasing pressure of stringent environmental regulations. Furthermore, they are rather inefficient. Therefore, there is an urgent need for environmentally friendly and sustainable corrosion control strategies. The mechanisms of microbially influenced corrosion and microbially influenced corrosion inhibition are not completely understood, because they cannot be linked to a single biochemical reaction or specific microbial species or groups. Corrosion is influenced by the complex processes of different microorganisms performing different electrochemical reactions and secreting proteins and metabolites that can have secondary effects. Information on the identity and role of microbial communities that are related to corrosion and corrosion inhibition in different materials and in different environments is scarce. As some microorganisms are able to both cause and inhibit corrosion, we pay particular interest to their potential role as corrosion-controlling agents. We show interesting interfaces in which scientists from different disciplines such as microbiology, engineering and art conservation can collaborate to find solutions to the problems caused by corrosion.

Biofilms: strategies for metal corrosion inhibition employing microorganisms

Corrosion causes dramatic economic loss. Currently widely used corrosion control strategies have disadvantages of being expensive, subject to environmental restrictions, and sometimes inefficient. Studies show that microbial corrosion inhibition is actually a common phenomenon. The present review summarizes recent progress in this novel strategy: corrosion control using beneficial bacteria biofilms. The possible mechanisms may involve: (1) removal of corrosive agents (such as oxygen) by bacterial physiological activities (e.g., aerobic respiration), (2) growth inhibition of corrosion-causing bacteria by antimicrobials generated within biofilms [e.g., sulfate-reducing bacteria (SRB) corrosion inhibition by gramicidin S-producing Bacillus brevis biofilm], (3) generation of protective layer by biofilms (e.g., Bacillus licheniformis biofilm produces on aluminum surface a sticky protective layer of gamma-polyglutamate). Successful utilization of this novel strategy relies on advances in study at the interface of corrosion engineering and biofilm biology.

Novel Steel Corrosion Protection by Microbial Extracellular Polymeric Substances (EPS) – Biofilm-Induced Corrosion Inhibition

Microbially influenced corrosion (MIC) of steel has gained increasing attention in recent years because the damage caused by this process is a significant cost factor for industry. Consequently, inhibition of corrosion and especially the development of corrosion protective films is an important present-day research topic. In this connection, application of microbially produced EPS for mitigating steel corrosion is an innovative idea. However, observations of ”protective” biofilms on metallic surfaces have been previously reported. Their inhibiting effect is generally thought to be caused by oxygen depletion or the formation of passivating layers. In contrast to many conventional corrosion protective methods, EPS or EPS-derived agents would be a cheap and environmentally friendly solution. Extensive research activities are still required, before biofilms or cell-free EPS can be used for corrosion protection on larger scale. In this study, we are developing a novel EPS-based corrosion protection method for unalloyed and corrosion resistant steel in aqueous media, which is based upon the application of microbial metabolic products. EPS of various sulfatereducing bacteria and other microorganisms are investigated for their inhibiting effect. The extent of such inhibition is evaluated in a model test system, in which different steels are subjected to corrosive conditions under sulfate-reducing conditions. To elucidate the protective mechanisms, comparative analyses of the chemical composition of the applied EPS are performed.

Phylogenetic analysis of a biofilm bacterial population in a water pipeline in the Gulf of Mexico

The aim of this study was to assess the bacterial diversity associated with a corrosive biofilm in a steel pipeline from the Gulf of Mexico used to inject marine water into the oil reservoir. Several aerobic and heterotrophic bacteria were isolated and identified by 16S rRNA gene sequence analysis. Metagenomic DNA was also extracted to perform a denaturing gradient gel electrophoresis analysis of ribosomal genes and to construct a 16S rRNA gene metagenomic library. Denaturing gradient gel electrophoresis profiles and ribosomal libraries exhibited a limited bacterial diversity. Most of the species detected in the ribosomal library or isolated from the pipeline were assigned to Proteobacteria (Halomonas spp., Idiomarina spp., Marinobacter aquaeolei, Thalassospira sp., Silicibacter sp. and Chromohalobacter sp.) and Bacilli (Bacillus spp. and Exiguobacterium spp.). This is the first report that associates some of these bacteria with a corrosive biofilm. It is relevant that no sulfate-reducing bacteria were isolated or detected by a PCR-based method. The diversity and relative abundance of bacteria from water pipeline biofilms may contribute to an understanding of the complexity and mechanisms of metal corrosion during marine water injection in oil secondary recovery.

Aluminum- and mild steel-binding peptides from phage display

Using a phage library displaying random peptides of 12 amino acids on its surface, several peptides were found that bind to aluminum and mild steel. Like other metal-binding peptides, no obvious consensus motif has been found for these peptides. However, most of them are rich in hydroxyl-containing amino acids, serine or threonine, or contain histidine. For the aluminum-binding peptides, peptides with a higher number of hydroxyl-containing amino acids bind to the aluminum surface more tightly. For example, Val-Pro-Ser-Ser-Gly-Pro-Gln-Asp-Thr-Arg-Thr-Thr, which contains five hydroxyl-containing amino acid residues, was selected four-fold more frequently than a peptide containing only one serine, suggesting an important role for the hydroxyl-containing amino acids in the metal-peptide interaction.

Gene expression in Bacillus subtilis surface biofilms with and without sporulation and the importance of yveR for biofilm maintenance

Five independent DNA microarray experiments were used to study the gene expression profile of a 5-day Bacillus subtilis air-liquid interface biofilm relative to planktonic cells. Both wild-type B. subtilis and its sporulation mutant (DeltaspoIIGB::erm) were investigated to discern the important biofilm genes (in the presence and absence of sporulation). The microarray results indicated that suspension cells were encountering anaerobic conditions, and the air-liquid interface biofilm was metabolically active. For the statistically significant differential expression (P < 0.05), there were 342 genes induced and 248 genes repressed in the wild-type biofilm, whereas 371 genes were induced and 128 genes were repressed in the sporulation mutant biofilm. The microarray results were confirmed with RNA dot blotting. A small portion of cells (1.5%) in the wild-type biofilm formed spores and sporulation genes were highly expressed. In the biofilm formed by the sporulation mutant, competence genes (comGA, srfAA, srfAB, srfAD, and comS) were induced which indicate a role for quorum sensing (bacterial gene expression controlled by sensing their population) in biofilms. There were 53 genes consistently induced in the biofilms of both the wild-type strain and its spoIIGB mutant-those genes have functions for transport, metabolism, antibiotic production-and 26 genes with unknown functions. Besides the large number of genes with known functions induced in the biofilm (121 genes in the wild-type biofilm and 185 genes in the sporulation mutant biofilm), some genes with unknown functions were also induced (221 genes in the wild-type biofilm and 186 genes in the sporulation mutant biofilm), such as the yve operon which appears to be involved in polysaccharide synthesis and the ybc operon which inhibits the growth of competitors for nutrients. A knockout mutant of yveR was constructed, and the mutant showed major defects in biofilm maintenance. Both the wild-type strain and its sporulation mutant formed normal biofilms, suggesting complete sporulation is not necessary for biofilm formation. The expression profiles of these two strains share more repressed genes than induced genes, suggesting that the biofilm cells repress similar pathways in response to starvation and high cell density.

Inhibiting mild steel corrosion from sulfate-reducing and iron-oxidizing bacteria using gramicidin-S-producing biofilms

A gramicidin-S-producing Bacillus brevis 18-3 biofilm was shown to reduce corrosion rates of mild steel by inhibiting both the sulfate-reducing bacterium Desulfosporosinus orientis and the iron-oxidizing bacterium Leptothrix discophora SP-6. When L. discophora SP-6 was introduced along with D. orientis to a non-antimicrobial-producing biofilm control, Paenibacillus polymyxa ATCC 10401, a corrosive synergy was created and mild steel coupons underwent more severe corrosion than when only D. orientis was present, showing a 2.3-fold increase via electrochemical impedance spectroscopy (EIS) and a 1.8-fold difference via mass-loss measurements. However, when a gramicidin-S-producing, protective B. brevis 18-3 biofilm was established on mild steel, the metal coupons were protected against the simultaneous attack of D. orientis and L. discophora SP-6. EIS data showed that the protective B. brevis 18-3 biofilm decreased the corrosion rate about 20-fold compared with the non-gramicidin-producing P. polymyxa ATCC 10401 biofilm control. The mass loss for the protected mild steel coupons was also significantly lower than that for the unprotected ones (4-fold decrease). Scanning electron microscope images corroborated the corrosion inhibition by the gramicidin-S-producing B. brevis biofilm on mild steel by showing that the metal surface remained untarnished, i.e., the polishing grooves were still visible after exposure to the simultaneous attack of the sulfate-reducing bacterium and the iron-oxidizing bacterium.

(5Z)-4-bromo-5-(bromomethylene)-3-butyl-2(5H)-furanone reduces corrosion from Desulfotomaculum orientis

(5Z)-4-bromo-5-(bromomethylene)-3-butyl-2(5H)-furanone (furanone) from the red marine alga Delisea pulchra was found previously to inhibit the growth, swarming and biofilm formation of Gram-positive bacteria (Ren et al., 2002, Lett Appl Microbiol 34: 293-299). In the present study, the Gram-positive sulphate-reducing bacterium (SRB), Desulfotomaculum orientis, was used to study the inhibition of mild steel corrosion due to the addition of furanone. The weight loss from batch coupon experiments incubated with 40 microg x ml(-1) furanone was reduced fivefold compared with samples that lacked furanone. Analysis of the metal surface with environmental scanning electron microscopy further confirmed the protection afforded by the addition of furanone. In agreement with the corrosion inhibition, most probable number (MPN) analysis showed that 20 and 40 microg x ml(-1) furanone inhibited 58% and 96% of the D. orientis growth respectively. Hence, furanone has the potential to inhibit microbial-induced corrosion related to Gram-positive bacteria.

Inhibition of biofilm formation and swarming of Bacillus subtilis by (5Z)-4-bromo-5-(bromomethylene)-3-butyl-2(5H)-furanone

AIMS

(5Z)-4-Bromo-5-(bromomethylene)-3-butyl-2(5H)-furanone(furanone) of the marine alga Delisea pulchra was synthesized, and its inhibition of swarming motility and biofilm formation of Bacillus subtilis was investigated.

METHODS AND RESULTS

Furanone was found to inhibit both the growth of B. subtilis and its swarming motility in a concentration-dependent way. In addition, as shown by confocal scanning laser microscopy, furanone inhibited the biofilm formation of B. subtilis. At 40 microg ml(-1), furanone decreased the biofilm thickness by 25%, decreased the number of water channels, and reduced the percentage of live cells by 63%.

CONCLUSIONS, SIGNIFICANCE AND IMPACT OF THE STUDY

Natural furanone has potential for controlling the multicellular behaviour of Gram-positive bacteria.

Inhibition of biofilm formation and swarming of Escherichia coli by (5Z)-4-bromo-5-(bromomethylene)-3-butyl-2(5H)-furanone

The quorum-sensing disrupter (5Z)-4-bromo-5-(bromomethylene)-3-butyl-2(5H)-furanone (furanone) of the alga Delisea pulchra was found to inhibit the swarming motility of Escherichia coli completely at 13 microg cm-2 (also at 20 microg ml-1) but did not inhibit its growth rate at 13-52 microg cm-2 or from 20 to 100 microg ml-1. Swimming was not inhibited by the furanone at 20-40 microg ml-1. In addition, confocal scanning laser microscopy revealed that this furanone at 60 microg ml-1 inhibited the biofilm formation of E. coli, as it decreased its thickness by 55%, reduced the number of water channels and decreased the percentage of live cells by 87%. This suggests that natural furanone may be used as a new method to control bacterial biofilms that does not involve toxicity. Furanone at 10 microg ml-1 also inhibited by 3300-fold the quorum sensing of Vibrio harveyi via autoinducer 1 (AI-1) and inhibited by 5500-fold that of V. harveyi via of autoinducer 2 (AI-2) as well as inhibited by 26-600-fold the quorum sensing of E. coli via AI-2; hence, this furanone is a non-specific intercellular signal antagonist.

Structural analysis of a biofilm which enhances carbon steel corrosion in nutritionally poor aquatic environments

Carbon steel coupons were exposed to nutritionally-poor synthetic wastewater inoculated with activated sludge from a municipal waste water plant. Biofilm formation was observed after one day incubation, and the thickness of the film increased proportionally with the incubation period. Mass loss of the coupons was also proportional to the incubation time, and reached 70.4 (mg/cm2) after incubation for 140 d. The observed mass loss was 5 times as much as that under sterile conditions. To characterize the microbiologically influenced corrosion (MIC) of carbon steel, structural analysis of the biofilm was performed. Rapid decrease in the dissolved oxygen (DO) concentration in the zone near the surface of the biofilm was observed by a microelectrode mounted on a micromanipulator. Heterogeneous distribution of the DO concentration on the surface of the steel plate was observed after multiple analyses. The heterogeneous structure of the biofilm composed of viable cells, inanimate objects, voids and pores was elucidated by confocal scanning laser microscopy. Concentrations of both aerobic bacteria and sulphur-reducing bacteria in the biofilm decreased with the incubation time, indicating that the increase in the biofilm thickness reflected an increase in the density of dead microbial cells or in extracellular polymer accumulation by the microbes. The average roughness of the metal surface observed after 112 d of incubation was +/-7.14 microm, which was 14.1% of the average thickness of the coupons. These observations indicated that uneven distribution of the DO profile and the cell concentration were critical for MIC of the carbon steel.