Christine C. Gaylarde

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.

Microbial Deterioration of Stone Monuments : An Updated Overview

Cultural heritage monuments may be discolored and degraded by growth and activity of living organisms. Microorganisms form biofilms on surfaces of stone, with resulting aesthetic and structural damage. The organisms involved are bacteria (including actinomycetes and cyanobacteria), fungi, archaea, algae, and lichens. Interactions between these organisms and stone can enhance or retard the overall rate of degradation. Microorganisms within the stone structure (endoliths) also cause damage. They grow in cracks and pores and may bore into rocks. True endoliths, present within the rock, have been detected in calcareous and some siliceous stone monuments and are predominantly bacterial. The taxonomic groups differ from those found epilithically at the same sites. The nature of the stone substrate and the environmental conditions influence the extent of biofilm colonization and the biodeterioration processes. A critical review of work on microbial biofilms on buildings of historic interest, including recent innovations resulting from molecular biology, is presented and microbial activities causing degradation are discussed.

CONSIDERATION OF SOME IMPLICATIONS OF THE RESISTANCE OF BIOFILMS TO BIOCIDES

Abstract Biofilms are considered as the growth of cells at a surface with the production of extracellular polymeric substances. Biofilm formation has serious implications in industrial, environmental, public health and medical situations. There is now a large body of evidence and thus concern that microorganisms within biofilms (including certain pathogenic microorganisms) are less susceptible to the activity of biocides than their planktonic counterparts. The mechanisms of bacterial resistance to some antibacterial agents such as many antibiotics are reasonably well-understood. The extensive exopolysaccharide polymer associated with biofilms is considered as a potential barrier which can hinder or prevent biocides from reaching target organisms within the biofilm, but the actual physical barrier properties of the biofilm may be of less importance and it now seems that perhaps the intrinsic (phenotypic) resistance to biocides, shown by cells within a biofilm, is of primary concern to researchers in the field. Nutrient limitation and reduced growth rates resulting from the position of bacteria within a biofilm are considered to influence the physiology of bacteria which in turn alters their sensitivity to biocides. When these phenomena are coupled with the ability of both Gram-positive and Gram-negative bacteria to communicate with each other in a cell-density-dependent or growth phase manner via diffusible communication molecules, it is becoming obvious that individual biofilm organisms may be able to behave as sociable, collective communities to regulate their gene expression in order to control various physiological processes and responses, in aid of the ‘common good’. Since most antimicrobial agents have been developed as a consequence of their activities against relatively fast-growing planktonic organisms, this approach is unlikely to be entirely suitable for the development of biocides against sessile biofilm organisms. Thus, the generation of biofilms which are representative of their true nature in the environment and which are suitable for the evaluation of the effects of biocides is essential in biocide research and development but it is not an easy task, as every application involving problematic biofilm formation will probably represent a unique niche which will require individual solutions. Disruption of a biofilm prior to assessing the viability of individual members by conventional microbiological methods is not considered ideal for the evaluation of biocides. There is a need for the development of non-disruptive methods for the measurement of biofilm formation.

Deteriogenic biofilms on buildings and their control : A review

Concrete, stone, brick, plaster, wood, plastic, painted surfaces and metal are all colonised by bacteria, algae and fungi which accelerate theirdeterioration. The mechanisms of deterioration, the main microbial genera involved and factors which may affect the degree of colonisation and attack are discussed. The chief factor determining microbial growth on constructional materials is moisture. Thus it is important for architects and engineers to consider critical points in the humidity profile of a building at the design stage. Damp surfaces are readily colonised by microbial cells settling from the air. This leads to the formation of a biofilm, which can trap dust and other particulate materials, increasing its disfiguring effect. In addition, the biofilm can act as a reservoir for potentially dangerous microorganisms such as the bacteria responsible for legionnaires’ disease and allergenic fungal and actinomycete spores. Materials may be protected against microbial growth by the use of biocides. The use ...

Algal and cyanobacterial biofilms on calcareous historic buildings.

Major microorganisms in biofilms on external surfaces of historic buildings are algae, cyanobacteria, bacteria, and fungi. Their growth causes discoloration and degradation. We compared the phototrophs on cement-based renderings and limestone substrates at 14 historic locations (47 sites sampled) in Europe and Latin America. Most biofilms contained both cyanobacteria and algae. Single-celled and colonial cyanobacteria frequently constituted the major phototroph biomass on limestone monuments (32 sites sampled). Greater numbers of phototrophs, and especially of algae and of filamentous morphotypes, were found on cement-based renderings (15 sites), probably owing to the porosity and small pore size of the latter substrates, allowing greater entry and retention of water. All phototrophic groups were more frequent on Latin American than on European buildings (20 and 27 sites, respectively), with cyanobacteria and filamentous phototrophs showing the greatest differences. The results confirm the influence of both climate and substrate on phototroph colonization of historic buildings.

Biodeterioration of stored diesel oil: studies in Brazil

Abstract The problems of hydrocarbon fuel storage in Brazil are particularly acute for diesel fuel. Visits to bus depots showed that many foremen did not understand the importance of draining water bottoms regularly and most systems were microbially contaminated. Common fungal isolates from refineries and distribution systems, Hormoconis resinae , Aspergillus niger , Aspergillus fumigatus , Paecilomyces variotii , and Candida silvicola , grew equally well in laboratory diesel/water systems with or without a chemical additive mixture, showing that this package of compounds neither promoted nor retarded fungal growth. Non-sterilised diesel was stored for 450 days over a water bottom, with or without an isothiazolone biocide, in the laboratory. The fungi most frequently detected in the non-biocide treated systems were H. resinae , A fumigatus , P. variotii , a Penicillium sp., and the yeasts, Rhodotorula glutinis and Candida silvicola . Bacterial isolates included oxidative Gram negative rods, sulphate-reducing bacteria and a Micrococcus sp. Biocide at 0.1 ppm maintained the systems clean for up to 30 days, and at 1 or 10 ppm for 400 days. After 400 days, the biomass (dry weight) from non-additive-containing diesel in control, 1 and 10 ppm biocide-containing systems was 24.6, 4.6 and 3.3 mg, respectively. The system treated with 0.1 ppm biocide yielded 38.2 mg biomass, indicating that sub-effective doses may lead to increased microbial growth. Within 24 h of addition of 10 ppm biocide to a highly contaminated control flask (145 days storage) there was a 2-log reduction in total aerobic bacterial and yeast population and the filamentous fungal count was >5 ml −1 .

Fungal colonization and succession on newly painted buildings and the effect of biocide

This report describes the sequence of fungal colonization and the influence of biocide incorporation on paint films, determined using quantitative methods. Two buildings were painted with an acrylic paint, with and without an experimental biocide formulation containing a carbamate (carbendazin), N-octyl-2H-isothiazolin-3-one and N-(3,4-dichlorophenyl)N,N-dimethyl urea (total biocide concentration 0.25% w/w). One week after painting, the major groups of organisms detected were yeasts and Cladosporium. The yeast population fell to undetectable levels after the third week and this microbial group was not detected again until the 31st week, after which they increased to high levels on the 42nd week. Aureobasidium showed a pattern similar to the yeasts. The main fungal genera detected over the 42-week period were Alternaria, Curvularia, Epicoccum, Helminthosporium, Coelomycetes (mainly Pestalotia/Pestalotiopsis), Monascus, Nigrospora, Aureobasidium and Cladosporium. The latter was the main fungal genus detected at all times. The physiological factors controlling colonization are discussed. Cladosporium, Aureobasidium, Tripospermum and yeasts on the painted surfaces were all able to grow on mineral salts agar containing 10% sodium chloride. This is the first time that the genus Tripospermum has been reported on painted buildings. The fungal population on biocide-containing surfaces was significantly lower than on non-biocide-containing paint after 13 weeks and continued so to 42 weeks after painting, but there was no statistically significant difference in the level of fungal biodiversity.

Algae and cyanobacteria on painted buildings in Latin America

The algal and cyanobacterial types present on discoloured surfaces of painted buildings in five Latin American countries, Argentina, Bolivia, Brazil, Mexico and Peru, were examined. The biofilms were found to contain algae, cyanobacteria, protozoa, fungi, slime moulds, actinomycetes and other bacterial groups. A total of 1363 different morphotypes were detected at 88 sites. Of these, 63.4% were non-filamentous genera and 61.9% of the total phototrophs were cyanobacteria. Synechocystis-like forms were the most biodiverse, often comprised the major biomass and were present in 64.8% of sites. Oscillatoriales were the next most diverse group. The algal genus, Chlorella, showed the most widespread occurrence (68.2% of sites). A significantly lower percentage of the population (55.8%) was composed of cyanobacteria in residential as compared with urban and rural locations, probably because of better building maintenance in the former. The implications of the results for standard algicide testing are discussed.

Phototrophic biofilms on ancient Mayan buildings in Yucatan, Mexico.

Abstract. Buildings at the important archaeological sites of Uxmal and Kabah, Mexico, are being degraded by microbial biofilms. Phospholipid fatty acid (PLFA) and chlorophyll a analyses indicated that phototrophs were the major epilithic microorganisms and were more prevalent on interior walls than exterior walls. Culture and microscopical techniques showed that Xenococcus formed the major biomass on interior surfaces, but the stone-degrading genera Gloeocapsa and Synechocystis were also present in high numbers. Relatively few filamentous algae and cyanobacteria were detected. The fatty acid analysis also showed that complex biofilms colonize these buildings. Circular depressions observed by scanning electron microscopy (SEM) on stone and stucco surfaces beneath the biofilm corresponded in shape and size to coccoid cyanobacteria. SEM images also demonstrated the presence of calcareous deposits on some coccoid cells in the biofilm. Phototrophic biofilms may contribute to biodegradation by (1) providing nutrients that support growth of acid-producing fungi and bacteria and (2) active “boring” behavior, the solubilized calcium being reprecipitated as calcium carbonate.

Biodegradation of the herbicide trifluralin by bacteria isolated from soil

Trifluralin (alpha,alpha,alpha-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine; TFL) is a pre-emergence, soil-incorporated herbicide that has been in agricultural use since the early 1960s and is moderately persistent in soil. The purpose of this study was to isolate and characterise TFL-resistant bacteria from a soil in which this pesticide has been used for the last four decades and to determine their ability to degrade TFL using HPLC. Eight bacteria were isolated by repeated subculture in liquid medium with TFL as carbon source and a ninth (isolate 9) from growth around TFL crystals on solid medium. The bacteria from enriched liquid culture were identified by biochemical tests and 16S rDNA sequencing. In a mineral salts medium with 0.1% succinate, 0.1% yeast extract and 50 mg l(-1) TFL, reductions in the level of pesticide of 24.6% for Klebsiella sp., 16.4% for Herbaspirillum sp., 25.0% and 16.0% for two strains of Bacillus sp. and 21.0% for unidentified isolate number 9 were obtained after 30 days. These were similar to the level obtained using a known TFL-degrading bacterium, Brevundimonas diminuta (NCIMB 10329). Three Pseudomonas sp. and one Bacillus sp. reduced levels by less than 5%. The five positive isolates can be used to study the biochemical and molecular biology of TFL biodegradation with the aim of optimising the degradative ability of one or more of the isolates for future use in bioremediation processes.