〔報告〕虎塚古墳公開保存施設の管理方法変更による微生物汚染状況の推移

The exhibition facility of Torazuka Tumulus constructed in October 1980 was recently contaminated by microbial colonization on the walls and ceiling even though periodic fungicidal treatment had been performed. Although there is no clear scientific researchabout the cause of the microbial contamination, it can be inferred that the increase of fungicide-resistant microbes may have been associated with the long-time use of fungicide. Because of this unfavorable situation, the committee for the conservation of historic sites in Hitachinaka city decided to change the fungicidal treatment for controlling microbes to exhaustive cleaning in November 2011 according to the concept of integratedpest management. In the present study, we aimed to monitor the changes of microbial contamination, more specifically of air-borne fungal concentration, in indoor air at the exhibition facility of Torazuka Tumulus. The culturable air-borne fungal concentration in indoor air of the facility gradually increased until March 2013 after discontinuing fungicidal treatment. However, air-borne fungi decreased in October 2013 and were lowest in March 2014.Exhaustive cleaning wasperformed two times (October 2013 and March 2014) and air-borne fungal concentration significantly decreased after the cleaning. From these results it is considered that periodic cleaning for removing the microbes and organic substances supporting microbial growth is one of the effective countermeasures for controlling microbial contamination in the exhibition facility of TorazukaTumulus although further monitoring of the microbial contamination is still necessary

〔報告〕虎塚古墳石室の扉石表面に形成したバイオフィルムの微生物群集構造解析とその制御

A processing trace left on the door stone of the Torazuka Tumulus at the time it was made is conserved in the exhibition facility built inside the burial mound of the tumulus. Although a periodic fungicidal treatment had been performed, the surface of the door stone was recently covered with microbial biofilms and fungal mycelium. Microbial colonization may cause not only biodeterioration of valuable stone surface but also disturbance of appreciation for viewers. For these reasons, culture-independent analysis was performed to reveal microbial communities in the biofilm. Furthermore, the respiration rate was measured before and after UV irradiation to assess the effect of the biofilm sterilization.From the result of culture-independent analysis, it was found that the DNA in the biofilm contained bacterial sequences related to those of Chryseolinea sp. (14%) and Methylacidiphilum sp.(9%)and fungal sequences related to those of Exophiala sp.(95%)and Cladophialophora sp.(7%).It was found that UV irradiation treatment had almost no effect on the biofilm sterilization because the respiration rate was increased after the treatment.Physical removal by manual labor was eventually chosen for removing the biofilm on the door stone. It was an effective method for decreasing the biofilm directly and for microbiological control in the long term by depleting the source of nutrition for heterotrophic microbes. On the other hand, repeated physical treatment has possibilities for artificial deterioration of the surface of the door stone. It will therefore be necessary to argue studiously about the tool, method, and frequency

〔報文〕虎塚古墳の壁画剥落片の微生物群集構造解析

The present research conducted microbial community analysis on small fragments collected from the Torazuka Tumulus to clarify the structure of microbial communities on wall paintings without biodeterioration by using molecular biological methods.As a result of quantitative PCR using the DNA solution extracted from the small pieces of wall paintings, the number of fungal 18S rRNA genes within all samples were less than that of bacterial 16S rRNA genes.The results from the next-generation sequencing of viruses have shown that the following phyla have appeared frequently in all samples: Proteobacteria (relative abundance 27.9%-50.9%), Bacteroidetes (8.8%-46.9%), Planctomycetes (3.2%-15.1%) and Acidobacteria (2.2%-3.7%). Genus Reyranella in phylum Proteobacteria and genus Chryseolinea in phylum Bacteroidetes have shown the highest relative abundance within all samples.Results from the clone library analysis have shown that the genus Exophiala had the highest relative abundance within all samples. As Exophiala has also been isolated from the Takamatsuzuka Tumulus, Kitora Tumulus, and Lascaux cave, it was suggested that stone surfaces such as burial mounds are favorable habitats for Exophiala.In the future, it is necessary to clarify the interaction between the bacteria and fungi from small fragments using the culturing methods. Furthermore, basic research such as the abundance of bacteria and fungi in stone chambers, and their interaction with biological communities, including soil animals, is needed. These studies are expected to provide important knowledge to understand local conservation methods for wall paintings in the Torazuka Tumulus

〔報告〕結露が古墳壁画に及ぼす影響に関する基礎実験

In recent years, it has been reported that the mural paintings of Torazuka Tumulus in Ibaraki prefecture might have faded. Dew condensation can be one of the reasons for this degradation phenomenon. In order to investigate the influence of dew condensation on mural paintings, laboratory experiments were conducted in the present study.For the experiments, test pieces reproducing the structure of Torazuka mural paintings were prepared. A test piece was composed of a tuff stone, white substrate layer and red pigments. Two test pieces were set in a closed space where the relative humidity was kept at 100%, and one of the test pieces was cooled by using a Peltier module device to make dew condensation occur on its surface. Dew condensation on the surface of the test piece was identified by measuring weight and water content of the test piece as well as the water transfer in the vicinity of the surface of the test piece.The influence of dew condensation on the substrate layer and pigment was investigated by comparing photographs taken before and after the experiments. However, no influence was recognized in these experiments