Oxygen and pH microprofiles above corroding mild steel covered with a biofilm

O₂ and pH microprofiles were measured above corroding mild steel covered with a biofilm. The pH in the anodic areas (tubercles) ranged from 5 to 7 and was always 9.45 at the surface of the cathodic areas. After 1 month of biofilm development, O₂ was depleted at the anodic area but could reach the cathodic surface where it was reduced. Consequently, differential O₂ concentration cells were the driving force for corrosion. The O₂ microprofiles indicated that O₂ was consumed in the tubercles, probably by microbial activity, while O₂ was reduced electrochemically in the cathodic areas. It was concluded that O₂ transfer to the cathodic surface was the rate limiting step for the corrosion process.     

First air-tolerant effective stainless steel microbial anode obtained from a natural marine biofilm

Microbial anodes were constructed with stainless steel electrodes under constant polarisation. The seawater medium was inoculated with a natural biofilm scraped from harbour equipment. This procedure led to efficient microbial anodes providing up to 4 A/m² for 10 mM acetate oxidation at −0.1 V/SCE. The whole current was due to the presence of biofilm on the electrode surface, without any significant involvement of the abiotic oxidation of sulphide or soluble metabolites. Using a natural biofilm as inoculum ensured almost optimal performance of the biofilm anode as soon as it was set up; the procedure also proved able to form biofilms in fully aerated media, which provided up to 0.7 A/m². The current density was finally raised to 8.2 A per square meter projected surface area using a stainless steel grid. The inoculating procedure used here combined with the control of the potential revealed, for the first time, stainless steel as a very competitive material for forming bioanodes with natural microbial consortia.     

Viability of a marine microbial biofilm

The formation of a microbial biofilm on glass surfaces arranged in lamellar piles parallel with circulating sea water (3 cm·sec^–1) was studied. The increase in dry weight, protein content, nucleotide content (ATP, ADP), and diatoms was followed over a period of 62 days. Dry weight and protein were estimates of the total biofilm development, whereas the nucleotide measurements revealed the viability of the biofilm and reflected the dynamics in the community structure.     

Phylogenetic diversity of a SRB-rich marine biofilm

This study was conducted to characterize the phylogenetic diversity of a corrosive marine biofilm based on 16S rDNA. Results of phylogenetic analysis indicated that, out of the 112 clones developed, 52 clones (46.4%) were affiliated with two families of sulfate-reducing bacteria: Desulfovibrionaceae and Desulfobacteriaceae. Another 44 clones (39.3%) were affiliated with the Clostridiaceae family of low G+C, gram-positive bacteria. Three clones (2.7%) were closely related to Chlorobium vibrioforme, a green sulfur bacterium.     

Neutrophilic iron-oxidizing "zetaproteobacteria" and mild steel corrosion in nearshore marine environments

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.     

Monitoring of a Vibrio natriegens and Desulfovibrio vulgaris marine aerobic biofilm on a stainless steel surface in a laboratory tubular flow system

N.D. BENBOUZID-ROLLET, M. CONTE, J. GUEZENNEC AND D. PRIEUR. 1991. In an aerobic bulk environment sulphate-reducing bacteria (SRB) can find suitable growth conditions on surfaces where other micro-organisms have developed an extensive biofilm. On metal surfaces they may induce or enhance corrosion. A laboratory tubular flow system was designed to study this phenomenon by creating a biofilm on stainless steel under dynamic conditions with Vibrio natriegens and Desulfovibrio vulgaris. The sulphate reducer colonized the surface, constituting approximately 5% of the total population. Its in situ growth rate, calculated by a simplified mathematical model, showed that the attached SRB multiplied at their settling locations. No significant difference with respect to corrosion enhancement was found in the electrochemical reactions of the metal betwen the control and the reactor, where D. vulgaris was present in the biofilm.     

Substratum-induced morphological changes in a marine bacterium and their relevance to biofilm structure.

The effects of surfaces on the physiology of bacteria adhering to surfaces or immobilized within biofilms are receiving more interest. A study of the effects of hydrophobic and hydrophilic substrata on the colonization behavior of a marine bacterium, SW5, revealed major differences in the morphology of SW5 on these surfaces. Using epifluorescence, scanning confocal laser, and on-line visualization (time-lapse video) microscopy, the organisms at hydrophobic surfaces were characterized by the formation of tightly packed biofilms, consisting of single and paired cells, whereas those at hydrophilic surfaces exhibited sparse colonization and the formation of chains more than 100 microns long, anchored at the surface by the terminal (colonizing) cell. The results are discussed in terms of the possible factors inducing the observed morphological differences and the significance of these differences in terms of biofilm structure and plasmid transfer when SW5 is the recipient organism.     

Age-related reproductive variation in a wild marine mammal population

Life history theory predicts a change in reproduction success with age as energy resources are limited and must be allocated effectively to maximize reproduction and survival. In this study, we use three reproductive performance measures, maternal expenditure, offspring weaning mass, and first-year survival, to investigate the role that maternal age plays in successful reproduction. Long-term uninterrupted life history data available for Marion Island’s southern elephant seals and mass change estimates from photogrammetry data allow for assessment of age-related reproduction performance and trade-offs. Known-aged adult females were photographed for photogrammetric mass estimation (n = 29) and their pups weighed at weaning during the 2009 breeding season. Maternal age and proportional mass loss positively influenced pup weaning mass. In turn, first-year pup return rates (as a proxy for survival) were assessed through the intensive mark–recapture program. Pup survival increased with female age and weaning mass. Pups of young females aged 3–6 years have a lower first-year survival probability compared with pups of older and larger females.     

Effect of temperature on biofilm formation by Antarctic marine bacteria in a microfluidic device

Polar biofilms have become an increasingly popular biological issue because new materials and phenotypes have been discovered in microorganisms in the polar region. Various environmental factors affect the functionality and adaptation of microorganisms. Because the polar region represents an extremely cold environment, polar microorganisms have a functionality different from that of normal microorganisms. Thus, determining the effective temperature for the development of polar biofilms is crucial. Here, we present a simple, novel one-pot assay for analysis of the effect of temperature on formation of Antarctic bacterial biofilm using a microfluidic system where continuous temperature gradients are generated. We find that a specific range of temperature is required for the growth of biofilms. Thus, this microfluidic approach provides precise information regarding the effective temperature for polar biofilm development with a new high-throughput screening format.     

Metabolic dynamics of Desulfovibrio vulgaris biofilm grown on a steel surface

In this study, a comparative metabolomics approach combining gas chromatography–mass spectrometry (GC-MS) and liquid chromatography–mass spectrometry (LC-MS) was applied first between planktonic cells and biofilms and then between pure cultures and biofilms of Desulfovibrio vulgaris. The results revealed that the overall metabolic level of the biofilm cells was down-regulated, especially for metabolites related to the central carbon metabolism, compared to the planktonic cells and the pure culture of D. vulgaris. In addition, pathway enrichment analysis of the 58 metabolites identified by GC-MS showed that fatty acid biosynthesis in the biofilm cells was up-regulated, suggesting that fatty acids may be important for the formation, maintenance and function of D. vulgaris biofilm. This study offers a valuable perspective on the metabolic dynamics of the D. vulgaris biofilm.     

Unexpected fine-scale population structure in a broadcast-spawning Antarctic marine mollusc

Several recent empirical studies have challenged the prevailing dogma that broadcast-spawning species exhibit little or no population genetic structure by documenting genetic discontinuities associated with large-scale oceanographic features. However, relatively few studies have explored patterns of genetic differentiation over fine spatial scales. Consequently, we used a hierarchical sampling design to investigate the basis of a weak but significant genetic difference previously reported between Antarctic limpets (Nacella concinna) sampled from Adelaide and Galindez Islands near the base of the Antarctic Peninsula. Three sites within Ryder Bay, Adelaide Island (Rothera Point, Leonie and Anchorage Islands) were each sub-sampled three times, yielding a total of 405 samples that were genotyped at 155 informative Amplified Fragment Length Polymorphisms (AFLPs). Contrary to our initial expectations, limpets from Anchorage Island were found to be subtly, but significantly distinct from those sampled from the other sites. This suggests that local processes may play an important role in generating fine-scale population structure even in species with excellent dispersal capabilities, and highlights the importance of sampling at multiple spatial scales in population genetic surveys.     

Biocidal effect of cathodic protection on bacterial viability in biofilm attached to carbon steel

Biofilm formed on carbon steel by various species of bacterial cells causes serious problems such as corrosion of steel, choking of flow in the pipe, deterioration of the heat-transfer efficiency, and so on. Cathodic protection is known to be a reliable method for protecting carbon steel from corrosion. However, the initial attachment of bacteria to the surface and the effects of cathodic protection on bacterial viability in the biofilm have not been clarified. In this study, cathodic protection was applied to an artificial biofilm containing Pseudomonas aeruginosa (PAO1), a biofilm constituent, on carbon steel. The aims of this study were to evaluate the inhibition effect of cathodic protection on biofilm formation and to reveal the inhibition mechanisms. The viability of PAO1 in artificial biofilm of 5 mm thickness on cathodically protected steel decreased to 1% of the initial cell concentration. Analysis of pH distribution in the artificial biofilm by pH microelectrode revealed that pH in proximity to carbon steel increased to approximately 11 after cathodic protection for 5 h. Moreover, 99% of region in the artificial biofilm was under the pH conditions of over nine. A simulation of pH profile was shown to correspond to experimental values. These results indicate cells in the artificial biofilm were killed or damaged by cathodic protection due to pH increase.     

The potential of and limitations to marine population prognosis

Following the 19th century recognition and definition of basic ecological entities, functional analysis has been the highlight of this century. The synthesis of these findings enables ecological prognosis. The population as the basic functional unit has been repeatedly treated; in the marine field, fisheries management approaches developed into multi-species population analysis. As in planktology, theoretical ecology, and classic biocoenotic research, the population interactions are of increasing scientific interest. A mathematical model is suggested that combines these extrinsic and intrinsic functional relationships in order to define the fit of the ecological niche to the environment, the decisive measure of the expected population success, and thus of the probable population development needed for prognostic purposes. It is discussed in how far the orientation towards the predictive power or — with respect to the “skill” of meteorological prognoses — the “ecological prognostic skill” improvement may serve as a means to choose the best investigative strategy.     

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.     

Adhesion of Desulfovibrio desulfuricans and Pseudomonas fluorescens to mild steel surfaces

The adhesion of micro-organisms to metal surfaces has been shown to be important in the corrosion process, but the cell surface structures participating in this adhesion have not previously been identified. Evidence is presented that a bacterial substance taking part in the initial adhesion of Pseudomonas fluorescens and Desulfovibrio desulfuricans (New Jersey) to mild steel is polysaccharide in nature. It is likely that this is present in the outer membrane of the bacterial cells as lipopolysaccharide.     

Sex-biased marine survival and growth in a population of coho salmon

Examination of historical records for coho salmon in Big Beef Creek, in western Washington, U.S.A., indicated that more adult males than females returned to spawn, and that the mean length of the females exceeded that of males. Sex-biased survival and faster growth among females are unusual among salmonids but precedented in some other coho salmon populations. To help determine the stage of life at which sex-biased mortality might occur, the sex-linked GH-ψH pseudogene was used to determine the sex of smolts emigrating from Big Beef Creek in 1995–1997. In each of the 3 years the sex ratio was indistinguishable from 50:50, indicating similar survival rates in fresh water, and implying that the male and female coho salmon follow different foraging strategies when they are at sea. The female strategy apparently results in greater mortality, but benefits survivors with greater size. The male strategy appears to allow greater survival at the cost of reduced size.     

Rapid succession within the Veillonella population of a developing human oral biofilm in situ

Streptococci are the primary component of the multispecies oral biofilm known as supragingival dental plaque; they grow by fermentation of sugars to organic acids, e.g., lactic acid. Veillonellae, a ubiquitous component of early plaque, are unable to use sugars; they ferment organic acids, such as lactate, to a mixture of shorter-chain-length acids, CO₂, and hydrogen. Certain veillonellae bind to (coaggregate with) streptococci in vitro. We show that, between 4 and 8 hours into plaque development, the dominant strains of Veillonella change in their phenotypic characteristics (coaggregation and antibody reactivity) as well as in their genotypic characteristics (16S RNA gene sequences as well as strain level fingerprint patterns). This succession is coordinated with the development of mixed-species bacterial colonies. Changes in community structure can occur very rapidly in natural biofilm development, and we suggest that this process may influence evolution within this ecosystem.     

Isolation and characterization of a marine methanogenic bacterium from the biofilm of a shiphull in Los Angeles harbor

A marine mesophilic, irregular coccoid methanogen, which shows close resemblance toMethanococcus sp., was isolated from the biofilm of shiphulls docked in Los Angeles harbor. Hydrogen plus carbon dioxide or formate served as substrates for methanogenesis in a mineral salt medium. The isolate did not use acetate and methanol as sole source of carbon and energy. The organism had an optimal pH range of 6.8–7.0 and a temperature optimum of 37°C. Elevated levels of sodium chloride were required for optimum growth. Optimum levels of total sulfide and magnesium chloride for growth were 1.0mm and 10mm respectively. The isolate used ammonia as nitrogen source. The concentration of 30mm ammonium chloride supported maximum growth of the isolate.