キトラ古墳における菌類等生物調査報告（2）

Excavation of Kitrora Tumulus started at the end of January 2004. As some parts of its plaster walls with beautiful mural paintings had become detached, it was decided to relocate such parts from their stone support and to restore them in a safe environment. This report describes the biological issues encountered during restoration work. In the course of the excavation of the tumulus and the restoration of the mural paintings in early 2004, some moulds such as Trichoderma sp., Penicillium sp. and Fusarium sp. were seen inside the tumulus. Phialocephala sp., which is a very tough mould, was also found on stones in the front room. At the end of 2004, dark coloured moulds such as Cylindrocarpon sp. also started to be seen in the tumulus. A bacterium, Bacillus megaterium, which secreted brown coloured substances, was isolated from a piece of paper which had been used to consolidate fragile parts on the plaster. In early 2005, small colonies of viscous gel started to be seen on some parts of the walls. Such gel was a mixture of some bacteria and fungi, Acremonium sp., etc. Therefore, such colonies were treated with about 70% volume ethanol – 0.3% formalin. Insects were also found often in the tumulus during spring and early summer. In the summer of 2005, the viscous gel suddenly increased to form "biofilm" on the plaster walls. It was very viscous, covering parts of the walls, and 70% volume ethanol was not effective to remove it. In September 2005, investigation of such substances inside the tumulus was performed with the help of specialists on microbes or microbial control. With their advice, the bilfilm was removed, where it was possible, with a low concentration of hydrogen peroxide solution, then treated with about 70% of isopropyl alcohol. Such method was effective on some parts where plaster was relatively intact and robust, but it could not be applied to places where plaster was very fragile, for example on the south wall that had a very precious painting of aphoenix. Furthermore, in the fall of 2005, small holes with black substances inside became obvious on the plaster walls. It seemed that the hole had developed from the back side of the plaster. By investigation, a specialist on microbes in concrete suggested that such holes might have been caused by some activity of microbes at places with small spaces on the back side of the plaster. It is very important to relocate the mural paintings as soon as possible and to keep them in a safe environment in order to protect such paintings from quick break down by microbial attack.