Iwona B. Beech

Recent advances in the study of biocorrosion: an overview

Biocorrosion processes at metal surfaces are associated with microorganisms, or the products of their metabolic activities including enzymes, exopolymers, organic and inorganic acids, as well as volatile compounds such as ammonia or hydrogen sulfide. These can affect cathodic and/or anodic reactions, thus altering electrochemistry at the biofilm/metal interface. Various mechanisms of biocorrosion, reflecting the variety of physiological activities carried out by different types of microorganisms, are identified and recent insights into these mechanisms reviewed. Many modern investigations have centered on the microbially-influenced corrosion of ferrous and copper alloys and particular microorganisms of interest have been the sulfate-reducing bacteria and metal (especially manganese)-depositing bacteria. The importance of microbial consortia and the role of extracellular polymeric substances in biocorrosion are emphasized. The contribution to the study of biocorrosion of modern analytical techniques, such as atomic force microscopy, Auger electron, X-ray photoelectron and Mossbauer spectroscopy, attenuated total reflectance Fourier transform infrared spectroscopy and microsensors, is discussed.

Corrosion of technical materials in the presence of biofilms—current understanding and state-of-the art methods of study

Abstract It is documented that biofilms are capable of influencing electrochemical processes at the metal surface, often leading to deterioration of metals referred to as biocorrosion or microbiologically influenced corrosion. Biofilms typically consist of microbial cells and their metabolic products including extracellular polymers, and inorganic precipitates. Interaction of biofilms and exopolymers with metal ions has long been proposed as one of the mechanisms of metal biodeterioration. This paper presents an overview of the application of modern microscopy and surface analysis techniques in studying the involvement of biofilms and extracellular polymeric material in the biocorrosion process of metals and their alloys.

Interactions of exopolymers produced by sulphate-reducing bacteria with metal ions

The aim of this study was to determine the effect of metal species such as Cr, Ni and Mo on growth and on the production of exopolymeric substances (EPS) in batch cultures of two strains of marine sulphate-reducing bacteria (SRB) isolated from corrosion failures in Portsmouth (UK) and Indonesia. In addition, the ability of EPS released into the liquid phase of the bacterial growth media to complex Cr, Ni and Mo, was investigated using atomic absorption spectroscopy. Results demonstrated that metals influence both SRB growth and exopolymer production and that the effect of the metal species on bacterial metabolism depends on the type of SRB. The presence of Cr, Ni and Mo was detected in EPS recovered from 3 day old SRB cultures. Although concentrations of these elements in exopolymers varied with metal species and with the SRB isolate, levels of Mo associated with EPS were significantly higher than the measured amount of Cr or Ni, regardless of the bacterial isolate.

The use of atomic force microscopy for studying interactions of bacterial biofilms with surfaces

Biofilms formed in different environments under either field or laboratory conditions on naturally occurring and man-made surfaces have been extensively studied in various stages of their development using a wide range of microscopy techniques. The majority of these methods are, however, qualitative and, with the exception of scanning electron microscopy (SEM), do not provide information on the effect that the biofilm exerts on the underlying substratum. In contrast, atomic force microscopy (AFM) has proven to be a potent tool for characterising, both qualitatively and quantitatively, aspects of biofilm/substratum interactions. This communication provides an overview of the application of AFM for the investigation of bacterial biofilms focusing on specific studies related to metallic surfaces such as stainless steel and copper alloys in freshwater and marine environments.

Chemical and structural characterization of exopolymers produced by Pseudomonas sp. NCIMB 2021 in continuous culture

The growth of marine Pseudomonas sp. NCIMB 2021 as continuous cultures in the presence of surfaces of AISI 316 stainless steel allowed the isolation and partial chemical characterization of exopolymers released into the culture medium (free exopolymers), as well as capsular and biofilm exopolymers. Fourier-transform infrared (FTIR) spectroscopy demonstrated the presence of O- and N-acetylation within the carbohydrate moieties and a predominant 310-helical structure of the protein component, highly resistant to hydrogen/deuterium exchange. Differences between the exopolymers were apparent. Relatively less uronic acid residues were detected in the capsular exopolymers compared to either the biofilm or free exopolymers. O- and N-acetylation were greatest in the biofilm exopolymer. SDS-PAGE protein profiles confirmed differences between exopolymers. The secondary structures of proteins determined using FTIR spectroscopy indicated that the capsular exopolymer had reduced helical content and an increased aggregated strand content compared to the biofilm exopolymer. However, the free exopolymer had an increased beta-sheet component and a reduced unordered component when compared to the biofilm and capsular exopolymers. These data suggest that exopolymer chemistry varies with cellular mode of growth.

Characterisation of exopolymers produced by different isolates of marine sulphate-reducing bacteria

This study was undertaken to investigate the influence of carbon steel surfaces on the yield and composition of exopolymers (EPS) secreted by two different isolates of marine sulphate-reducing bacteria (SRB) recovered from severe corrosion failures and to establish whether the yield and the type of EPS varied between these isolates. SRB were purified and grown in the laboratory as static batch cultures with and without the presence of carbon steel surfaces. Characterisation of EPS harvested from the bulk phase of the cultures revealed the presence of carbohydrates, proteins and nucleic acids. Colorimetric and gas chromatographic analysis of EPS polysaccharides showed that although their composition was similar for both SRB isolates, they were synthesised in different quantities. Furthermore, the presence of carbon steel surfaces influenced the type of polysaccharide produced by the SRB. Examination of the EPS protein profiles has revealed the appearance of new bands in exopolymers harvested from bacterial cultures grown with carbon steel. The amount and type of nucleic acid in the EPS varied between the cultures. The results demonstrate the difference in EPS composition between SRB isolates and the ability of SRB to modify their physiological response in the presence of a carbon steel surface. The implication of such modification for the phenomenon of SRB influenced corrosion of carbon steel is discussed.

Study of the interaction of sulphate-reducing bacteria exopolymers with iron using X-ray photoelectron spectroscopy and time-of-flight secondary ionisation mass spectrometry.

Time-of-flight secondary ionisation mass spectrometry and X-ray photoelectron spectroscopy were employed to determine the interaction of crude extracellular polymeric substances recovered from static batch cultures of two isolates of marine sulphate-reducing bacteria of the genus Desulfovibrio, grown in the presence of and without mild steel surfaces, with Fe ions released from steel. The results demonstrated that exopolymers synthesised by different strains of sulphate-reducers varied in their ability to bind iron originating from steel. Based on the X-ray photoelectron spectroscopy analysis it is proposed that Fe released from steel was associated with bacterial exopolymers such as Fe(III) ion. The application of surface science techniques to study exopolymer/metal interaction allowed quantitative evaluation of Fe binding using small sample size.

The development of a method to evaluate bioreceptivity of indoor mortar plastering to fungal growth

The aim of this work was to develop and standardise an accelerated laboratory test for detecting bioreceptivity of indoor mortar to fungal growth. To determine which fungal species were predominant under field conditions, isolation was carried out using mortar samples collected from 41 buildings in two cities of Sao Paulo State in the South East of Brazil. Cladosporium was found to be the genus most frequently recovered from field specimens. Based on the results of laboratory trials strain C. sphaerospermum was chosen as a test microorganism. Four different mortars, two laboratory-manufactured mortars composed of ordinary Portland cement, high calcium hydrated lime and standardised sand, and two different ready-mixed building mortars from the Brazilian market, were investigated for their susceptibility to colonisation by C. sphaerospermum. Several parameters were tested to determine factors influencing fungal bioreceptivity. The type of mortar, degree of carbonation and pH values of mortars, as well as relative humidity of environment effected colonisation of C. sphaerospermum. All except one mortar samples showed significant fungal growth, however, the growth occurred only at 100% relative humidity. Interaction of C. sphaerospermum with mortar specimens was studied using techniques of scanning and environmental scanning electron microscopy combined with energy dispersive X-ray analysis.

MASE1 and MASE2: Two Novel Integral Membrane Sensory Domains

Escherichia coli proteins YegE and YaiC contain N-terminal integral membrane regions, followed by the putative diguanylate cyclase (GGDEF, DUF1) domains. The membrane domains of these proteins, named MASE1 (membrane-associated sensor) and MASE2, respectively, were found in other bacterial signaling proteins, such as histidine kinases (MASE1) and an adenylate cyclase (MASE2). Although the nature of the signals sensed by MASE1 and MASE2 is still unknown, MASE1-containing receptors appear to play important roles in bacteria, including iron and/or oxygen sensing by hemerythrine-containing proteins in the sulfate-reducing bacterium Desulfovibrio vulgaris.

An atomic force microscopy study of the biodeterioration of stainless steel in the presence of bacterial biofilms

Atomic Force Microscopy (AFM), a technique requiring little or no preparation of biological samples prior to viewing and allowing observation of bacteria and bacterial expolymers in their hydrated forms, has been used to elucidate the phenomena of stainless steel corrosion due to the development of bacterial biofilms. Biofilms formed by pure and mixed cultures of Pseudomonas aeruginosa, the sulphate-reducing bacterium Desulfovibrio gigas and a consortium isolated from a corroding, cast iron pipe carrying potable water were grown for 7 and 14 days in batch cultures at 25°C on surfaces of stainless steel (316) coupons, polished to obtain a 1 μm finish. Surfaces with biofilms present and removed were examined by AFM and by scanning electron microscopy (SEM). The study revealed that the greatest deterioration of steel, in a form of pitting corrosion, occurred in the presence of an isolated pipe consortium. The degree of corrosion observed in mixed cultures of P. aeruginosa and D. gigas was higher than that recorded in pure cultures of these bacteria. The advantage of using AFM as a qualitative method of biocorrosion assessment and its potential for quantitative analysis of microbially influenced corrosion are emphasised.