Characterization of the algal flora growing on ancient Roman frescoes

Abstract

The walls of some rooms of the Domus aurea in Rome (Italy) have several remarkable paintings of the Roman age, which are attributed by the archaeologists to a painter named Fabullus (Bor­ da 1958). This monument was opened to the visitors from 1950 to 1981, and during that time green crusts of biological nature developed on some frescoes. In order to stop the biodeterio­ ration, the incandescent lamps within the rooms were switched off. Nevertheless the crusts re­ mained and became larger and the frescoes were further damaged. At the request of the Istituto Centrale del Restauro of Rome we have carried out research in order to determine the charac­ teristics of the algal biocenosis that is growing on the walls with and without frescoes. For the investigation, we chose the eighty-fifth room of the Domus aurea where the relative hu­ midity approaches 95%, the temperature is ap­ proximately 18°C, and natural light intensity is less than 10 lux. The air comes from the outside through holes in the ceiling of the neighbouring room, since room 85 has no outside door. The artificial lighting previously used had an intensity of 145-150 lux at the surface with frescoes, and of 1 10 lux below the lamp on the walls without frescoes. Corresponding with the lighted areas there are several crusts, 1-2 mm deep, different in colour and causing different degrees of dete­ rioration. Samples were collected to the right (sample 1, blue-green), above (sample 2, dark green) and to the left of the lamp (sample 3, blue­ green). The last sample (sample 4, grey-brown) was taken below the lamp from an area without frescoes where the crust was hardly visible (Fig. 1). Samples 1 and 3 were soft and moist, while sample 4 was drier and rich in mineral compo­ nents. The various algal taxa were very difficult to identify in the fresh samples because of the compact structure formed by the com penetration of microorganisms and due to the necessity to squeeze the material in order to reveal the char­ acteristic structures of single organisms. Obser­ vations were made with a Leitz Laborlux D light microscope and a Leitz Orthoplan ft.uorescent microscope Ploemopak 2 with filter set 546 nm, and barrier filter 580 nm. Scanning electron mi­ croscopy was carried out by means of a Scan­ nosan EM on either fresh samples or fixed sam­ ples in 3% glutaraldehyde in 0. 1 M sodium cacodylate buffer pH 6.9, dehydrated, critical point dried with CO2 and gold coated (Favali et al 1978). For cultures, 0.2 g of each sample were ground to a powder, suspended in 0.9% NaCI to a final volume of 10 ml and kept for 24 h at 18°C and 150 lux of light intensity (the correspondent PAR was 2.7 JLmol m-2 S-I). From this suspension I ml was inoculated onto a double series of Petri dishes containing the following media: BD (Bas­ lerova & Dvorakova 1962), BG 11 (Stanier et al 1971), Detmer (Tomaselli et al 1979), Kolkwitz (Tomaselli et aI1979), AN (Albertano et aI 1979), and BN (Albertano et aI1979). The cultures were