International Biodeterioration最新文献

The heterotrophic bacteria population occurring on decaying sandstone from ancient monuments has been examined. Quantitative and qualitative observations are presented for seasonal variation over a period of 1 year. The diversity of heterotrophs occurring on sandstone was assessed on a monthly basis using a range of isolation media. An increase in numbers of bacteria was seen during the winter months: with both Gram-negative and Gram-positive types present. Gram-positive bacteria, especially spore-formers of the genus Bacillus, were found exclusively in the dry summer months. Decay activity, reflecting the potential of natural mixed populations present on the stone, also showed seasonal variation and this was related to the pattern of change for the bacterial species observed.

The efficacy of 4,5-dichloro-2-n-octyl-3(2H) isothiazolone (C9211) was determined using fungi isolated from food and drink processing plants. The anti-fungal performance of urethane oil based paints containing C9211 was tested in (a) laboratory experiments using a humidity cabinet and (b) field trials at a UK maltings establishment and in Singapore.

The surface of the hard glossy paints without biocide proved to be inhospitable for the germination and growth of mould fungi in exposures in the humidity cabinet and reasons for this are discussed. In field trials, paints without biocide developed extensive mould growth after several months exposure whilst all paints containing C9211 remained mould-free throughout the 18 month trial.

In the culture of Vibrio cholerae in saline water containing purified chitin prepared from fresh shrimp and crab shells, it was determined that the solubility of chitin in salin water is influenced more by the salinity than by the pH, with the optimum being pH 8·0 and salinity 15 o/oo. The stimulation of growth by freshly extracted chitins and commercially available preparations was similar. All chitin preparations stimulated growth somewhat less than did alkaline peptone broth (a commonly used culture medium). All chitin sources also stimulated the production of cholera toxin by toxigenic strains to about the same extent as did alkaline peptone broth. The strains were found to be very low toxin producers in filtered bay water alone, thus indicating the need for some nutrient source for this activity.

Polysaccharides were extracted from culture supernatants and biofilms on mild steel surfaces incubated for 7 and 28 days in pure and mixed cultures of Pseudomonas fluorescens and Desulfovibrio desulfuricans P. fluorescens produced the highest quantities of free extracellular polysaccharides (EPS) but yielded the lowest hexose content in biofilms. The major neutral hexoses detected in all extracted polysaccharides were glucose and mannose, glucose being prevalent in biofilms and mannose in free EPS. Uronic acids were found only in biofilm polysaccharides.

Scanning electron microscopy and kinetic polarisation studies showed that little corrosion occurred on mild steel incubated in P. fluorescens cultures. High levels of corrosion were seen in mixed and, to a somewhat greater extent, in pure D. desulfuricans cultures. Extracellular polysaccharides on metal surfaces help to maintain the structure of the biofilm and in this way may serve to facilitate corrosion. There is no correlation between the levels of free EPS and corrosion.

A study of the presence of cyanobacteria and algae in different building materials from Spain (Salamanca, Seville and Toledo Cathedrals) and Sweden (Lund Cathedral) and their possible relation to the stone decay was accomplished. Colonization of stone with the cyanobacterium Microcoleus vaginatus and the chlorophyte Klebsormidium flaccidum was also induced in the laboratory. In both field and laboratory samples, the microbial film, spontaneously detached, showed on its reverse side the presence of grains removed from the stone surface, thus causing mechanical deterioration on the colonized materials.

The mosaics from the Roman remains of Italica, which was founded in 206 BC near present-day Seville, are threatened by the ravages of nature that are destroying these masterpieces from the second century AD. Since the beginning of this century, the exposure of most of the mosaics after excavation has resulted in colonization by pioneering species of lichens and mosses, as well as by subsequent allied plants. The ultimate effect is the complete destruction of the mosaics, with some unfortunate examples being recorded.