International Biodeterioration最新文献

Microorganisms contribute substantially to the degradation of ceramic materials such as natural stone, concrete, ceramics and glass. Active attack is caused by excreted mineral or organic acids. Passive biodeterior results from excreted hydrophilic slimes of heteropolysaccharides and/or protein (biofilm).

All microorganisms may be of importance in biodeterioration - chemolithotrophic and chemoorganotrophic bacteria, cyanobacteria, algae, fungi and lichens. Recently it has become possible to test the resistance of ceramic materials to microbial attack. Using a simulation apparatus it is possible to demonstrate the interactions between a microorganism and its ceramic substratum. Purely chemical and/or physical testing of materials is not sufficient to determine their resistance to a biologically induced attack. Biogenic sulphuric acid corrosion and nitric acid corrosion simulation experiments have demonstrated differences in the resistance of various concretes, which chemical testing failed to reproduce.

Thus, biotest systems allow selection from many different materials so as to find the most appropriate.

A number of national and international methods developed during the last 15 years for evaluating the wet-state microbiological resistance of a wide range of aqueous formulations are compared and critically reviewed. General principles for testing the efficacy of biocidal additives in industrial aqueous-based products have been drawn from them and described. These principles were validated by the testing of five commonly available biocides in five different products. An emulsion paint, a metalworking fluid and a starch-based adhesive were tested for resistance to wet-state bacterial infection, and a bituminous emulsion and a ready-mixed ceramic tile adhesive were examined for resistance to wet-state surface fungal growth. The results not only indicate relative differences in the susceptibility of such products to microbiological infection but emphasise the effect of preconditioning the biocide in the test formulation prior to inoculation with the challenge organisms.

Fungal deteriogens occurring on the copper-chrome-arsenate treated service timber packing of two water cooling towers in Madras were studied over a period of 108 weeks. The present investigation adds 19 more species to the list of cooling tower soft rot fungi reported so far.

An account is presented of work undertaken to investigate the ability of sixteen bacteria to degrade polyester polyurethane. The results of liquid shake culture experiments using a mineral salts medium, incorporating the polyurethane as the sole carbon source, indicated that none of the bacteria were able to degrade the polyurethane over a 12-week period.

The addition of supplementary organic nutrients at a low level, achieved by the addition of 1 ml aliquots of overnight broth cultures of the bacteria to the shake cultures, was found to be sufficient to effect significant degradation in two isolates; a species of Corynebacterium and Pseudomonas aeruginosa (ATCC 13388) over a 12-week incubation period. The provision of higher levels of organic nutrients in the form of yeast extract (1% w/v) to the liquid shake cultures was found to effect significant degradation by a further five bacterial isolates.

Results are presented which indicate that four bacterial isolates could degrade the polyester polyurethane within 2 weeks in the presence of yeast extract.

Sporotrichum thermophile Apinis, was the most active carboxymethyl-cellulose (CMC)-ase producer among seven thermophilic and four thermotolerant fungal species isolated from Egyptian soil and screened for their ability to produce extracellular cellulase in culture media containing CMC as a sole carbon source. The fungus also efficiently hydrolysed filter paper cellulose. Comparison of various untreated and alkali-treated cellulosic and lignocellulosic materials as substrates for cellulase production by S. thermophile revealed the most easily degraded substrate was sugarcane bagasse at 2% concentration. This substrate when alkali treated was the most susceptible to enzymic hydrolysis by culture filtrates of S. thermophile grown on untreated bagasse. Optimum hydrolysis was obtained after 18 h incubation with the filtrate at pH 3·5–4 and 45°C. Alkali treatment of bagasse reduced its lignin content significantly and the culture filtrate of S. thermophile grown on untreated bagasse was found to contain xylanase and polygalacturonase in addition to cellulase and cellobiase.

A number of recently developed techniques which may be used for rapid quantification of total microbial activity or of specific microorganisms involved in corrosion are reviewed. These include viable counts using dip slides, microscope methods (epifluorescence), analysis of cell components (ATP, ergosterol, phospholipids), immunological methods (fluorescent antibody staining, ELISA), activity measurements (respiration, esterases, sulphate reduction) and the use of gene probes. The methods are discussed with reference to their simplicity, sensitivity, economics and applications.

Two moulds — Aspergillus flavus and Alternaria tenuissima — were isolated from wheat-based fast foods in Nigeria and their cultural conditions determined. A warm ascorbic acid environment is preferred by A. flavus but aeration enhances the growth of both organisms. At 45°C, Al. tenuissima is unaffected by vitamins. The minimum inhibitory concentrations of sodium chloride for A. flavus and Al. tenuissima are 5% and 10% w/v respectively. Lysine, casein hydrolysate, phenylalanine, raffinose, rhamnose and stachyose enhance growth in both species.

Mild steel and stainless steel samples were assayed in laboratory experiments against two different microbial strains isolated from cutting-oil emulsions: one strain of Pseudomonas fluorescens and a sulphate-reducing bacterium. The relationship between the corrosive attack and the formation of bacterial biofilms was assessed in each case by using electrochemical experiments complemented with scanning electron microscopical observation of the samples.