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Microbially influenced corrosion (MIC), is acknowledged to be the direct cause of catastrophic corrosion failures, with damages ranging to many billions of US$. In spite of extensive research and numerous publications, fundamental questions still remain unanswered. In 1993, J.F.D. Stott published a review paper in Corrosion Science, entitled “What progress in the understanding of microbially influenced corrosion has been made in the last 25 years?“ He concluded, “The most commonly asked question about MIC is: what will be the expected corrosion rate of material x in an environment where aggressive microorganisms proliferate?... For many materials we can no more answer this question now than we could 25 years ago.” Now, over 50 years later, that question is still open. Current MIC research does not provide data related to detection and verification in the field, diagnosing, modelling or prediction. Laboratory experiments seldom attempt to recreate relevant natural or industrial electrolytes. A sober, solution-oriented contemplation of the state-of-art and acknowledgement of the substantial deficiencies in our understanding may help shift MIC research into a direction which could actually produce useful answers.

Iron (Fe)- and manganese (Mn)-oxidizing bacteria are often cited individually and collectively as putative microorganisms for microbiologically influenced corrosion (MIC). The two groups of microorganisms have in common the ability to attach to surfaces and produce macroscopic accumulations (deposits) of metal oxides/hydroxides/oxyhydroxides that can influence corrosion of some metals and alloys in some environments. In all cases, once initiated, the corrosion is independent of the activities of the colonizing species. Despite the phylogenetic diversity of Fe-oxidizing bacteria (FeOB), the following sections will deal with corrosion mechanisms attributed to neutrophilic, lithotrophic, microaerophilic FeOB. The mineralogy of biologically oxidized Fe is consistent over a wide range of environments. All FeOB produce dense deposits that can cause corrosion of low alloy stainless steels (SS) directly, i.e., under-deposit corrosion. Association of Mn-oxidizing bacteria (MnOB) and other microorganisms may stabil...

Iron (Fe) oxides/oxyhydroxides in drinking water distribution systems (DWDS), produced by electrochemical, chemical, and biological reactions, can adsorb toxic metal ions, including strontium, lead, arsenic, and vanadium that, if desorbed, generate pulses of drinking water with elevated toxic metal ion concentrations. To illustrate that potential, sorption data for strontium (cation) and vanadium (oxyanion) in functioning DWDS are reviewed. In addition, the influence of flow/no flow on adsorption and desorption of strontium in a model DWDS is included. The reactions that influence adsorption and desorption within a DWDS are extremely complicated and poorly understood. The sorption capacity of Fe oxhydroxides varies with surface area, which in turn varies with source water and disinfectant. Desorption and release can be triggered by changes in source water, disinfection chemicals, or flow. Because of the interrelatedness of adsorption/desorption and Fe corrosion products, subtle changes in DWDS operating p...

Microbially influenced corrosion (MIC), is acknowledged to be the direct cause of catastrophic corrosion failures, with associated damage costs ranging to many billions of US$ annually. In spite of extensive research and numerous publications, fundamental questions relating to MIC remain unanswered. The following review provides an overview of current MIC research and stresses the lack of information related to MIC recognition, prediction and mitigation. The review establishes a link between management decisions and root causes. A holistic, proactive approach to MIC is suggested in which an entire system is considered, monitored and improved.

A perspective is provided on mechanisms for microbially influenced corrosion by sulfate-reducing bacteria and metal-oxidizing bacteria. The authors discuss the confusion introduced by cross-disciplinary discussions of MIC mechanisms and the divergent terminologies used by microbiologists and electrochemists, e.g. “anaerobic” and “direct electron transfer.” Examination of the cathodic depolarization theory for corrosion of carbon steel by sulfate-reducing bacteria suggests that the theory cannot explain the observations. Stainless steels containing

We, a group of concerned researchers and conservators, are very grateful to the 17th International Biodeterioration and Biodegradation Symposium (IBBS17) organizing committee and to the International Biodeterioration and Biodegradation Society president Brenda Little for giving us this opportunity to have a Panel Discussion on the “Past, Present and Future” of biodeterioration studies during the IBBS17 on September 6–8, 2017 in Manchester, U.K. A total of twenty-three of us, including a number of young scientists, joined the discussion and a few colleagues gave their inputs by mail in advance. It is our pleasure to summarize all information collected from the one-hour discussion in Manchester and to share them openly for future research planning and for establishment of a common ground to build new initiatives.

A multi-disciplinary investigation was undertaken to determine the cause of corrosion of iron nails from a skeletal structure in a museum setting. Corroded iron nails were removed from a large whale skeleton, that had been assembled in the 1930s and exhibited for over 80 years at the Natural History Museum in London, United Kingdom. Oxford Nanopore Technologies sequencing, SEM-EDS imaging and chemical mapping were used to document the fungal and bacterial communities associated with the corrosion of the iron nails. A mechanism for indoor fungal-mediated corrosion (biodeterioration) and biomineralisation of iron is proposed. The mechanism includes the establishment of a biofilm dominated by fungi, a corrosive electrolyte produced by fungal activities, transport of ions and biomineralisation of iron-rich minerals.

Meter length iron-rich rusticles on the RMS Titanic contain bacteria that reportedly mobilize iron from the ship structure at a rate that will reduce the wreck to rust in decades. Other sunken ships, such as the World War II shipwrecks in the Gulf of Mexico (GOM) are also similarly covered. However, at the GOM sites, rusticles are only centimeters in length. Minimal differences in water temperature (a few °C) between the two sites and comparable exposure times from wreckage to discovery cannot rationalize the extreme differences in rusticle length. One possible explanation for the observed difference in rusticle size is the differing amounts of dissolved or colloidal iron at the two locations.

The release of hydrocarbons and chemical dispersant in marine environments may disrupt benthic ecosystems, including artificial reefs, formed by historic steel shipwrecks, and their associated organisms. Experiments were performed to determine the impacts of crude oil, dispersed crude oil, and dispersant on the community structure and function of microorganisms in seawater (SW) and biofilms formed on carbon steel, a common ship hull construction material. Steel corrosion was also monitored to illustrate how oil spills may impact preservation of steel shipwrecks. Microcosms were filled with seawater (SW) and incubated at 4°C. Carbon steel disks (CSDs) were placed in each tank, and tanks were amended with crude oil and/or dispersant or no treatment. SW and CSD biofilms were sampled biweekly for genetic analysis using Illumina sequencing of 16S ribosomal RNA gene amplicons. Predicted and sequenced bacterial metagenomes were analyzed to examine impacts of oil and dispersant on metabolic function. Gammaproteobacteria, Alphaproteobacteria, and Flavobacteriia dominated SW and biofilms. Bacterial community structure differed significantly between treatments for SW and biofilms. OTUs affiliated with known (Pseudomonas) and potential (Marinomonas) hydrocarbon-degraders were roughly twice as abundant in biofilms treated with oil and dispersed oil, and steel corrosion of CSDs in these treatments was higher compared to control and dispersant treatments. OTUs affiliated with the Rhodobacteraceae family (biofilm formers and potential oil degraders) were less abundant in the dispersant treatment compared to other treatments in biofilm and SW samples, but OTUs affiliated with the Pseudoalteromonas genus (biofilm formers and proposed hydrocarbon degraders) were more abundant in dispersant-treated biofilms. Overall, functional gene analyses revealed a decrease in genes (predicted using PICRUSt and observed in sequenced metagenomes) associated with hydrocarbon degradation in dispersant-treated biofilms. This study indicates that exposure to oil and dispersant could disrupt the composition and metabolic function of biofilms colonizing metal hulls, as well as corrosion processes, potentially compromising shipwrecks as ecological and historical resources.

The pioneering work of Dickinson, et al., and other investigators in the Lewandowski research group at the Center for Biofilm Engineering, Montana State University, Bozeman, MT, provided a...

This study provides a physicochemical assessment of manganese deposits on brass and lead components from two fully operational drinking water distributions systems. One of the systems was maintained with chlorine; the other, with secondary chloramine disinfection. Synchrotron-based in-situ micro X-ray adsorption near edge structure was used to assess the mineralogy. In-situ micro X-ray fluorescence mapping was used to demonstrate the spatial relationships between manganese and potentially toxic adsorbed metal ions. The Mn deposits ranged in thickness from 0.01 to 400 μm. They were composed primarily of Mn oxides/oxhydroxides, birnessite (Mn(3+) and Mn(4+)) and hollandite (Mn(2+) and Mn(4+)), and a Mn silicate, braunite (Mn(2+) and Mn(4+)), in varying proportions. Iron, chromium, and strontium, in addition to the alloying elements lead and copper, were co-located within manganese deposits. With the exception of iron, all are related to specific health issues and are of concern to the U.S. Environmental Protection Agency (U.S. EPA). The specific properties of Mn deposits, i.e., adsorption of metals ions, oxidation of metal ions and resuspension are discussed with respect to their influence on drinking water quality.

Understanding the effect of conventional and alternative fuels on the marine bacterial community is crucial, as it pertains to the impact, biodegradation, and final fate of these fuels in the environment. Metagenomics analysis demonstrated that conventional and alternative fuels promoted the growth of Proteobacteria. Marinobacter and Desulfovibrio were predominant in seawater exposed to conventional jet propellant-5 (JP-5), while Hyphomonas and Rhodovulum were most abundant in seawater with hydroprocessed renewable jet fuel (HRJ) and conventional F-76 diesel, respectively. The phyla Bacteroidetes, Firmicutes, and Lentisphaerae were underrepresented in samples with fuel, and these phyla were largely comprised of unclassified bacteria. Culture-dependent tests isolated several of the same genera detected in high abundance by metagenomics DNA sequencing, including Marinobacter, Rhodovulum, and Halobacillus. Growth studies in fuel and gas chromatography analysis demonstrated that isolates grew in fuel and meta...

Addition of 1 g/L yeast extract (YE) to sterile, aerobic (approximately 21% dissolved oxygen) and deoxygenated (

Microbiologically influenced corrosion (MIC) can take place in any biologically active environment. The extreme conditions under which specific organisms can survive and/or grow and the possible environments for MIC are constantly being expanded. In all cases of MIC the failure mechanisms depend on the chemical nature of the environment, specific microorganisms growing in the environment, and the electrochemical properties of the reacting metals.

An Alteromonas macleodii strain was isolated from copper-containing coupons incubated in surface seawater (Key West, FL, USA). In addition to the original isolate, a copper-adapted mutant was created and maintained with 0.78 mM Cu2+. Biofilm formation was compared between the two strains under copper-amended and low-nutrient conditions. Biofilm formation was significantly increased in the original isolate under copper amendment, while biofilm formation was significantly higher in the mutant under low-nutrient conditions. Biofilm expression profiles of diguanylate cyclase (DGC) genes, as well as genes involved in secretion, differed between the strains. Comparative genomic analysis demonstrated that both strains possessed a large number of gene attachment harboring cyclic di-GMP synthesis and/or degradation domains. One of the DGC genes, induced at very high levels in the mutant, possessed a degradation domain in the original isolate that was lacking in the mutant. The genetic and transcriptional m...

Identification of any mechanism for microbiologically influenced corrosion (MIC) requires an understanding of the specificity of metal/microbe/electrolyte interactions. Recent advancements in our understanding of MIC are related to recognition of the implications of this specificity. For example, under some circumstances, nutrients can accelerate rates of corrosion. In other cases the oxyanions in nutrients can inhibit localised corrosion. In some environments the absence of oxidisable carbon can force a shift in electron donor and may result in more aggressive corrosion than in the presence of oxidisable carbon. Non-corrosive biofilms can become corrosive with subtle changes in the environment, e.g., addition of electron shuttle compounds. The list of electron donors and acceptors related to MIC has been expanded in recognition of the metabolic flexibility that has been demonstrated for microorganisms. Recent research on microbial fuel cells and microbial batteries has added to our understanding ...

Divalent cationic strontium (Sr 2+ ) adsorption to and desorption from iron corrosion products were examined in two model drinking water distribution systems (DWDS). One system was maintained with chlorine-disinfected drinking water and the other with the same water with secondary chloramine disinfection. Flow conditions simulated primary transmission lines (constant flow) and residential mains (periods of stagnation). Accumulation of Sr 2+ to iron corrosion products in model DWDS was independent of disinfection type. Adsorption and desorption mechanisms are discussed. X-ray adsorption near edge structure (XANES) spectroscopy and linear combination fitting determined Sr 2+ was primarily associated with iron oxyhydroxide corrosion products. At the end of the desorption study, the amount of Sr 2+ remaining in iron corrosion products equilibrated to approximate levels observed at the end of the constant flow adsorption experiments. These results suggest that enhanced iron corrosion product loading of Sr 2+ during stagnation could be short lived under constant flow conditions. Differences between adsorption and desorption based on disinfection type (chlorine versus chlorine plus chloramine) cannot be used to control Sr 2+ desorption.

Surfaces of carbon steel (CS) exposed to mixed cultures of iron-oxidizing bacteria (FeOB) and dissimilatory iron-reducing bacteria (FeRB) in seawater media under aerobic conditions were rougher than surfaces of CS exposed to pure cultures of either type of microorganism. The roughened surface, demonstrated by profilometry, is an indication of loss of metal from the surface. In the presence of CS, aerobically grown FeOB produced tight, twisted helical stalks encrusted with iron oxides. When CS was exposed anaerobically in the presence of FeRB, some surface oxides were removed. However, when the same FeOB and FeRB were grown together in an aerobic medium, FeOB stalks were less encrusted with iron oxides and appeared less tightly coiled. These observations suggest that iron oxides on the stalks were reduced and solubilized by the FeRB. Roughened surfaces of CS and denuded stalks were replicated with three culture combinations of different species of FeOB and FeRB under three experimental conditions. Measurements of electrochemical polarization resistance established different rates of corrosion of CS in aerobic and anaerobic media, but could not differentiate rate differences between sterile controls and inoculated exposures for a given bulk concentration of dissolved oxygen. Similarly, total iron in the electrolyte could not be used to differentiate treatments. The experiments demonstrate the potential for iron cycling (oxidation and reduction) on corroding CS in aerobic seawater media.

The relationship between corrosion and biodegradation of bio- and petroleum-based fuels was evaluated using aerobic seawater, fuel and unprotected carbon steel coupons under stagnant conditions to simulate a potential fuel storage condition. Aerobic respiration and corrosion reactions consumed oxygen in the incubations in a short time. The transient oxygen influenced the microbial biodegradation of all fuels and resulted in a suite of characteristic metabolites, including catechols. The corrosion was believed to be the result of biogenic sulfide production and in all cases, the black corrosion products contained chlorine and sulfur (presumed chloride and sulfide) in addition to iron. There were few differences in electrochemically measured corrosion rates in incubations amended with any of the fuels or their blends. Clone library analysis demonstrated higher proportions of Firmicutes, Deltaproteobacteria (primarily sulfate-reducing bacteria), Chloroflexi, and Lentisphaerae in incubations exposed to fuels than the original seawater. Relative proportions of sequences affiliated with these bacterial groups varied with fuel. Methanogen sequences similar to those of Methanolobus were also found in multiple incubations. Despite the dominance of characteristically anaerobic taxa, sequences coding for an alkane monooxygenase from marine hydrocarbon-degrading genera and aerobically produced intermediates were observed, indicative that organisms with this metabolic potential were active at some point during the incubation. Aerobic oxidation of fuel components resulted in the formation of a series of intermediates that could be used by anaerobic seawater microbial communities to support metabolism, sulfide production, and carbon steel corrosion.

The United States Environmental Protection Agency (US EPA) will require some U.S. drinking water distribution systems (DWDS) to monitor nonradioactive strontium (Sr(2+)) in drinking water in 2013. Iron corrosion products from four DWDS were examined to assess the potential for Sr(2+) binding and release. Average Sr(2+) concentrations in the outermost layer of the corrosion products ranged from 3 to 54 mg kg(-1) and the Sr(2+) drinking water concentrations were all ≤0.3 mg L(-1). Micro-X-ray adsorption near edge structure spectroscopy and linear combination fitting determined that Sr(2+) was principally associated with CaCO3. Sr(2+) was also detected as a surface complex associated with α-FeOOH. Iron particulates deposited on a filter inside a home had an average Sr(2+) concentration of 40.3 mg kg(-1) and the associated drinking water at a tap was 210 μg L(-1). The data suggest that elevated Sr(2+) concentrations may be associated with iron corrosion products that, if disturbed, could increase Sr(2+) concentrations above the 0.3 μg L(-1) US EPA reporting threshold. Disassociation of very small particulates could result in drinking water Sr(2+) concentrations that exceed the US EPA health reference limit (4.20 mg kg(-1) body weight).

Alteromonas macleodii is a marine bacterium involved in the early stages of biofouling on ship hulls treated with copper as an antifouling agent. We report here the draft genome sequences of an A. macleodii strain isolated from copper coupons and three laboratory mutants grown long-term at elevated copper levels.

The authors examined the physiochemical and microbiological properties of archived rusticles from World War II shipwrecks in the Gulf of Mexico. Rusticles, iron (Fe)-rich accumulations on shipwrecks in marine environments, have long been assumed to be the result of low alloy steel corrosion. In many cases the assumed corrosion has been attributed to biodeterioration because of the presence of specific types of bacteria associated with the rusticles. However, archived rusticles from WWII shipwrecks in the Gulf of Mexico (GOM) do not have the mineralogical layering typical of iron corrosion products. Moreover, spatial relationships between bacteria and rusticles cannot be interpreted as biodeterioration. The authors concluded that environmental Fe plays a role in rusticle formation and differences in Fe concentrations can be used to explain differences in rusticle size and distribution with depth in the GOM. Both biotic and abiotic mechanisms for Fe accumulation are provided.

Ennoblement, a positive shift in corrosion potential, due to biofilm formation is the basis of patents for biofilm monitoring and power generating devices. Ennoblement is a global phenomenon that is routinely cited as a mechanism for microbiologically influenced corrosion of some passive alloys. Increased corrosion is attributed to acceleration of the oxygen reduction reaction via several potential mechanisms that have been debated for decades. Because the phenomenon is predictable and reproducible at specific locations, ennoblement is the basis for patented methods and devices for monitoring biofilm formation and relating ennobled potentials to increased likelihood of corrosion and for evaluating cleaning and biocide treatments. Furthermore, when anodes and cathodes can be separated, as in a microbial fuel cell, biofilm formation on the cathode increases the potential difference between the two and the resulting power output. Most patented fuel cells using metal cathodes do not refer specifically to ennoblement in the disclosures.

Experiments were designed to evaluate the corrosion-related consequences of storing/transporting fatty acid methyl ester (FAME) alternative diesel fuel in contact with natural seawater. Coastal Key West, FL (KW), and Persian Gulf (PG) seawaters, representing an oligotrophic and a more organic- and inorganic mineral-rich environment, respectively, were used in 60 day incubations with unprotected carbon steel. The original microflora of the two seawaters were similar with respect to major taxonomic groups but with markedly different species. After exposure to FAME diesel, the microflora of the waters changed substantially, with Clostridiales (Firmicutes) becoming dominant in both. Despite low numbers of sulphate-reducing bacteria in the original waters and after FAME diesel exposure, sulphide levels and corrosion increased markedly due to microbial sulphide production. Corrosion morphology was in the form of isolated pits surrounded by an intact, passive surface with the deepest pits associated with the fuel/seawater interface in the KW exposure. In the presence of FAME diesel, the highest corrosion rates measured by linear polarization occurred in the KW exposure correlating with significantly higher concentrations of sulphur and chlorine (presumed sulphide and chloride, respectively) in the corrosion products.

Shewanella is a microbial genus that can oxidize lactate for the reduction of insoluble electron acceptors. This reduction is possible by either direct (cell–surface interaction, nanowires) or indirect (soluble redox mediators) mechanisms. However, the actual molecular identification of a nanowire has not been determined. Through mutational studies, Shewanella oneidensis MR-1 was analyzed for its ability to transfer electrons to an electrode after deletion of the structural pilin genes (ΔmshA-D) or the entire biosynthetic expression system (ΔmshH-Q) of one of its pilin complexes (Msh type IV pilus gene locus). The complete removal of the Msh complex (ΔmshH-Q) significantly decreased the current generated from a fuel cell compared to MR-1. However, the mutant with only extracellular Msh structural proteins removed (ΔmshA-D) was able to generate 80% of the current compared to MR-1. Thus, the intracellular and membrane bound Msh biogenesis complex is a pathway for extracellular electron transfer in S. oneidensis MR-1.

Microbiologically influenced corrosion (MIC) of mild steel in seawater is an expensive and enduring problem. Little attention has been paid to the role of neutrophilic, lithotrophic, iron-oxidizing bacteria (FeOB) in MIC. The goal of this study was to determine if marine FeOB related to Mariprofundus are involved in this process. To examine this, field incubations and laboratory microcosm experiments were conducted. Mild steel samples incubated in nearshore environments were colonized by marine FeOB, as evidenced by the presence of helical iron-encrusted stalks diagnostic of the FeOB Mariprofundus ferrooxydans , a member of the candidate class “ Zetaproteobacteria. ” Furthermore, Mariprofundus -like cells were enriched from MIC biofilms. The presence of Zetaproteobacteria was confirmed using a Zetaproteobacteria -specific small-subunit (SSU) rRNA gene primer set to amplify sequences related to M. ferrooxydans from both enrichments and in situ samples of MIC biofilms. Temporal in situ incubation studies showed a qualitative increase in stalk distribution on mild steel, suggesting progressive colonization by stalk-forming FeOB. We also isolated a novel FeOB, designated Mariprofundus sp. strain GSB2, from an iron oxide mat in a salt marsh. Strain GSB2 enhanced uniform corrosion from mild steel in laboratory microcosm experiments conducted over 4 days. Iron concentrations (including precipitates) in the medium were used as a measure of corrosion. The corrosion in biotic samples (7.4 ± 0.1 mM) was significantly higher than that in abiotic controls (5.0 ± 0.1 mM). These results have important implications for the role of FeOB in corrosion of steel in nearshore and estuarine environments. In addition, this work shows that the global distribution of Zetaproteobacteria is far greater than previously thought.

Shewanella-containing microbial fuel cells (MFCs) typically use the fresh water wild-type strain Shewanella oneidensis MR-1 due to its metabolic diversity and facultative oxidant tolerance. However, S. oneidensis MR-1 is not capable of metabolizing polysaccharides for extracellular electron transfer. The applicability of Shewanella japonica (an agar-lytic Shewanella strain) for power applications was analyzed using a diverse array of carbon sources for current generation from MFCs, cellular physiological responses at an electrode surface, biofilm formation, and the presence of soluble extracellular mediators for electron transfer to carbon electrodes. Critically, air-exposed S. japonica utilizes biosynthesized extracellular mediators for electron transfer to carbon electrodes with sucrose as the sole carbon source.

The structure and mineralogy of corrosion products formed on carbon steel coupons exposed in Duluth Superior Harbor (DSH, USA), were investigated and compared with corrosion products on similar substrata from other locations. Corrosion products in DSH form within a few months each year and are removed by ice scour and reform. The corrosion products formed in DSH are tubercles with an outer surface, an inner shell of magnetite, and a core of iron(III) oxyhydroxides, goethite, and lepidocrocite, in association with stalks produced by bacteria. In general, the tubercles formed in DSH are similar in morphology and mineralogy to corrosion products described for carbon steel and cast iron exposed to treated waters in decades-old drinking water and cooling water systems. DSH tubercles are unique in several structural details. DSH tubercles increase areal coverage of the substratum by consolidation of tubercles. Furthermore, the core material extends into the pit and is an exact replica of the pit profile.

Experiments were designed to evaluate the nature and extent of microbial contamination and the potential for microbiologically influenced corrosion of alloys exposed in a conventional high sulfur diesel (L100) and alternative fuels, including 100% biodiesel (B100), ultra-low sulfur diesel (ULSD) and blends of ULSD and B100 (B5 and B20). In experiments with additions of distilled water, all fuels supported biofilm formation. Changes in the water pH did not correlate with observations related to corrosion. In all exposures, aluminum 5052 was susceptible to pitting while stainless steel 304L exhibited passive behavior. Carbon steel exhibited uniform corrosion in ULSD and L100, and passive behavior in B5, B20, and B100.

The ability of the metal reducer Shewanella oneidensis MR-1 to generate electricity in microbial fuel cells (MFCs) depends on the activity of a predicted type IV prepilin peptidase; PilD. Analysis of an S. oneidensis MR-1 pilD mutant indicated that it was deficient in pili production (Msh and type IV) and type II secretion (T2S). The requirement for T2S in metal reduction has been previously identified, but the role of pili remains largely unexplored. To define the role of type IV or Msh pili in electron transfer, mutants that lack one or both pilus biogenesis systems were generated and analyzed; a mutant that lacked flagella was also constructed and tested. All mutants were able to reduce insoluble Fe(III) and to generate current in MFCs, in contrast to the T2S mutant that is deficient in both processes. Our results show that loss of metal reduction in a PilD mutant is due to a T2S deficiency, and therefore the absence of c cytochromes from the outer surface of MR-1 cells, and not the loss of pili or flagella. Furthermore, MR-1 mutants deficient in type IV pili or flagella generated more current than the wild type, even though extracellular riboflavin levels were similar in all strains. This enhanced current generating ability is in contrast to a mutant that lacks the outer membrane c cytochromes, MtrC and OmcA. This mutant generated significantly less current than the wild type in an MFC and was unable to reduce Fe(III). These results indicated that although nanofilaments and soluble mediators may play a role in electron transfer, surface exposure of outer membrane c cytochromes was the determining factor in extracellular electron transfer in S. oneidensis MR-1.

Field observations and laboratory testing were used to conclude that aggressive localized corrosion of carbon steel pilings in Duluth-Superior Harbor, Minnesota and Wisconsin, is caused by...

Changes in metabolism and cellular physiology of facultative anaerobes during oxygen exposure can be substantial, but little is known about how these changes connect with electrical current output from an operating microbial fuel cell (MFC). A high-throughput voltage based screening assay (VBSA) was used to correlate current output from a MFC containing Shewanella oneidensis MR-1 to carbon source (glucose or lactate) utilization, culture conditions, and biofilm coverage over 250 h. Lactate induced an immediate current response from S. oneidensis MR-1, with both air-exposed and anaerobic anodes throughout the duration of the experiments. Glucose was initially utilized for current output by MR-1 when cultured and maintained in the presence of air. However, after repeated additions of glucose, the current output from the MFC decreased substantially while viable planktonic cell counts and biofilm coverage remained constant suggesting that extracellular electron transfer pathways were being inhibited. Shewanella maintained under an anaerobic atmosphere did not utilize glucose consistent with literature precedents. Operation of the VBSA permitted data collection from nine simultaneous S. oneidensis MR-1 MFC experiments in which each experiment was able to demonstrate organic carbon source utilization and oxygen dependent biofilm formation on a carbon electrode. These data provide the first direct evidence of complex cellular responses to electron donor and oxygen tension by Shewanella in an operating MFC at select time points.

The following is a concise review of the literature that addresses the impact of marine biofilms on two phenomena—ennoblement of corrosion potential and sulfide derivitization due to sulfate-reducing bacteria. A universally defined mechanism of potential ennoblement has not been established. Extent of ennoblement varies among locations and the extent of ennoblement for a particular material cannot be used to predict an increased likelihood of localized corrosion. There is some controversy as to the susceptibility of low- and medium-grade stainless steels. Carbon steel and copper alloys are susceptible to sulfide derivitization but thermodynamic models cannot predict the susceptibility of these materials. Laboratory experiments designed to provide data on susceptibility to sulfide derivitization have produced conflicting results because of the following: (1) laboratory media can contain anions that inhibit localized corrosion, (2) laboratory media can contain yeast extract that interferes with electrochemical measurements, and (3) deaeration procedures can produce environments that are not conducive for the growth of sulfate-reducing bacteria. In general, alloys that undergo ennoblement are not vulnerable to sulfide derivitization and conversely, alloys that are subject to sulfide derivitization do not become ennobled.

It is our hypothesis that fermentative, acetogenic, and sulfate-reducing bacteria residing in pipeline facilities can influence corrosion through the production of carbon dioxide and acetate under the prevailing anaerobic conditions. The exacerbation of carbon dioxide corrosion of carbon steel in the presence of acetic acid is a well-known phenomenon in the oil industry. Both chemical compounds can be produced and consumed by microorganisms during the anaerobic biodegradation of organic matter—including hydrocarbons. We contend that the principles governing anaerobic biodegradation activity can be extrapolated to aboveground oil production facilities and that the microbial diversity inherent in petroleum reservoirs largely reflects that in pipelines.

A miniature-microbial fuel cell (mini-MFC, chamber volume: 1.2 mL) was used to monitor biofilm development from a pure culture of Shewanella oneidensis DSP10 on graphite felt (GF) under minimal nutrient conditions. ESEM evidence of biofilm formation on GF is supported by substantial power density (per device cross-section) from the mini-MFC when using an acellular minimal media anolyte (1500 mW/m 2 ). These experiments demonstrate that power density per volume for a biofilm flow reactor MFC should be calculated using the anode chamber volume alone (250 W/m 3 ), rather than with the full anolyte volume. Two oxygen reduction cathodes (uncoated GF or a Pt/vulcanized carbon coating on GF) were also compared to a cathode using uncoated GF and a 50 mM ferricyanide catholyte solution. The Pt/C-GF (2–4% Pt by mass) electrodes with liquid cultures of DSP10 produced one order of magnitude larger power density (150 W/m 3 ) than bare graphite felt (12 W/m 3 ) in this design. These advances are some of the required modifications to enable the mini-MFC to be used in real-time, long-term environmental power generating situations.

A miniature microbial fuel cell (mini-MFC) is described that utilizes an aerobic culture of Shewanella oneidensis DSP10 as the active electrochemical species in the anode chamber. We find that the maximum aerobic mini-MFC power without the addition of exogenous mediators was 0.40 mW, a 33% decrease when compared with an anaerobic DSP10 culture (0.6 mW) operating in the mini-MFC. This decrease is most likely due to the presence of dissolved oxygen in the anode chamber that scavenges electrons to form water, thereby reducing the number of electrons donated to the anode. Aerobic power and current density at maximum power using the true surface area of the anode (611 cm2) were calculated to be 6.5 mW m−2 and 13 mA m−2. The power density rises to 2.0 W m−2 and 330 W m−3 when calculated using the cross-sectional area and volume of the device (2 cm2, 1.2 cm3). The Coulombic efficiency was also reduced from 11 to 5% when using the aerobic versus anaerobic culture. Similar results were found when the external mediator anthraquinone-2,6-disulfonate (AQDS) was added to the aerobic culture, resulting in a maximum power of 0.54 mW, a 37% drop in power when compared to the anaerobic mediated system.

We demonstrate that Shewanella oneidensis , a metal-reducing bacteria species with cytoplasmic-membrane-bound reductases and remarkably diverse respiratory capabilities, reduced Cr(VI) to Cr(II) in anaerobic cultures where chromate was the sole terminal electron acceptor. Individual cell microanalysis by transmission electron microscopy (TEM) using electron energy-loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDXS) demonstrates Cr(II) concentrated near the cytoplasmic membrane, suggesting the terminal reduction pathway is intracellularly localized. Further, estimated cellular Cr(II) concentrations are relatively high at upwards of 0.03–0.09 g Cr/g bacterium. Accumulation of Cr(II) is observed in S. oneidensis cells prior to the formation of submicron-sized precipitates of insoluble Cr(III) on their surfaces. Furthermore, under anaerobic conditions, Cr(III) precipitates that encrust cells are shown to contain Cr(II) that is likely bound in the net negatively charged extracellular biopolymers which can permeate the surfaces of the precipitates. In otherwise nearly identical incubations, Cr(III) precipitate formation was observed in cultures maintained anaerobic with bubbled nitrogen but not in three replicate cultures in an anaerobic chamber.

The use of proton exchange membranes (PEMs) in biological fuel cells limits the diversity of novel designs for increasing output power or enabling autonomous function in unique environments. Here we show that selected nanoporous polymer filters (nylon, cellulose, or polycarbonate) can be used effectively in place of PEMs in a miniature microbial fuel cell (mini-MFC, device cross-section 2 cm2), generating a power density of 16 W/m3 with an uncoated graphite felt oxygen reduction reaction (ORR) cathode. The incorporation of polycarbonate or nylon membranes into biological fuel cell designs produced comparable power and durability to Nafion-117 membranes. Also, high power densities for novel larger (5 cm3 anode volume, 0.6 W/m3) and smaller (0.025 cm3 projected geometric volume, average power density 10 W/m3) chamberless and pumpless microbial fuel cells were observed. As an additional benefit, the nanoporous membranes isolated the anode from invading natural bacteria, increasing the potential applications for MFCs beyond aquatic sediment environments. This work is a practical solution for decreasing the cost of biological fuel cells while incorporating new features for powering long-term autonomous devices.

A thermophile,Thermus scotoductusSA-01, was cultured within a constant-temperature (65°C) microwave (MW) digester to determine if MW-specific effects influenced the growth and physiology of the organism. As a control,T. scotoductuscells were also cultured using convection heating at the same temperature as the MW studies. Cell growth was analyzed by optical density (OD) measurements, and cell morphologies were characterized using electron microscopy imaging (scanning electron microscopy [SEM] and transmission electron microscopy [TEM]), dynamic light scattering (DLS), and atomic force microscopy (AFM). Biophysical properties (i.e., turgor pressure) were also calculated with AFM, and biochemical compositions (i.e., proteins, nucleic acids, fatty acids) were analyzed by attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. Gas chromatography-mass spectrometry (GC-MS) was used to analyze the fatty acid methyl esters extracted from cell membranes. Here we report successful cultivation of a thermophile with only dielectric heating. Under the MW conditions for growth, cell walls remained intact and there were no indications of membrane damage or cell leakage. Results from these studies also demonstrated thatT. scotoductuscells grown with MW heating exhibited accelerated growth rates in addition to altered cell morphologies and biochemical compositions compared with oven-grown cells.