Of Microbes and Art The Role of Microbial Communities in the Degrada
Microbial defacement and degradation of artistic or historic artifacts is a worldwide problem affecting all countries regardless of their history, geographical location, or economic conditions. This is the first comprehensive study of the role of microbia
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Key words:
climatic factors, bacteria, biodeterioration, stone
Abstract:
Climate is recognised to play an important part in influencing the activity of microorganisms on stone in monuments and other objects of cultural value. In the UK and Greece, the numbers and distribution of heterotrophic bacteria were not strongly related to seasonal changes in temperature and rainfall. At Portchester Castle, qualitative changes in bacterial populations have been observed; actinomycetes were found only on decayed stone and dominant on stone from Tell Basta, in semi-arid Egypt. In the Minoan Palace at Petras and the fortifications ofKhania, higher counts of halotolerant heterotrophic bacteria were found in sheltered areas on stone showing other biological growths and salt effiorescence. For all monuments, stones oflower mechanical strength supported higher bacterial counts and electron microscopy showed extensive sheets ofbiofilm. Estimations of carbohydrate in stone could also be related to whether the sites were exposed or protected. There is evidence to suggest that variations in the nature of bacterial popUlations may be dependent on season in temperate regions and in the Mediterranean climate related to the location within the monument. Biofilm production and perhaps halotolerance provide means by which bacteria resist adverse changes in moisture levels. Extreme fluctuations in moisture may induce major shifts in bacterial populations selecting filamentous, sporeforming types that penetrate deeper into the stone.
49 O. Ciferri et al. (eds.), Of Microbes and Art © Springer Science+Business Media New York 2000
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Comparative studies of microbial communities
INTRODUCTION
Climate is recognised to play an important part in influencing the activity of microorganisms on stone in monuments and other objects of cultural value. Biodeterioration is a process involving several types of microorganisms, notably bacteria, fungi and algae in combination with lichens or mosses. Early workers suggested that the very presence of living organisms on stone increased its susceptibility to damage through their water-binding capacity. It has recently been suggested that the mineralogy, porosity, surface roughness and capacity to collect water and organic materials will control its bioreceptivity (Guillitte, 1995) and tendency to biodeterioration (Krumbein and Gobushina, 1995). However, environmental factors such as temperature, light intensity, pH and relative humidity will affect the number and types of colonising species (Tiano et aI., 1995) and hence the progress of the colonisation. Water is very important in causing the mechanical degradation of stone, controlling mainly porosity and bulk density (Turk and Dearman, 1986), while its circulation through stone is controlled by its porosity size, distribution, specific surface and capacity (Appolonia et aI., 1996). It promotes salt movement resulting in crystallisation and expansion due to changes in relative humidity (Puehringer, 1996) causing high shear strength forces (Fookes et
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