Characterisation of actinomycetes isolated from ancient stone and their potential for deterioration.

Actinomycetes have been isolated from decayed and sound stone samples taken from a tomb site at Tell Basta, Zagazig City, Egypt. A total of 160 isolates have been characterised. The numbers and distribution of actinomycetes were studied during different seasons; during the winter months (18-20 degrees C), actinomycete numbers ranged from 10(3) to 10(4) cfu/g; in the summer (28-38 degrees C) lower counts were recorded. The actinomycete isolates were assigned to 4 different taxonomic groups: 54% belonged to the Streptomyces group, 26% to the Nocardia group, 14% showed the characteristics of the Micromonospora group, while the rest of the isolates analyzed (6%) were assigned to the sporangiate-type group of actinomycetes. The ability of the isolates to produce pigments as well as tolerance to high salinity were determined. It was shown that about 88% of the strains studied had the ability to produce extracellular pigments. Only 25% of the studied isolates showed tolerance to high salinity. The significance of actinomycetes to attack and degrade building stone was shown in laboratory experiments: actinomycetes recovered both from sound and decayed stones were capable of damaging stone under laboratory conditions as an up to 4% weight loss was recorded for some isolates.