Microbial deterioration of tsunami-affected paper-based objects: A case study

•We described a unique microbial discoloration on the tunami-affected paper.•We identified a total of 48 strains isolated from the tunami-affected paper.•We could isolate the pigment-producing microbes from the discolored paper.•Most of the isolates showed a salt tolerance and cellulose-utilizing ability.•Initial responses to conserve the tunami-affected paper documents were proposed.

Huge numbers of cultural objects were damaged by microorganisms after having been soaked with seawater from the tsunami that followed the Great East Japan Earthquake on March 11, 2011. Among the cultural objects that were damaged, paper-based objects in the tsunami area were severely affected. In the present study, a culture-based analysis and on-site investigations were carried out to determine the extent of the microbial deterioration of paper-based objects (i.e., administrative documents and historical documents). Dark-colored fungi were isolated from black-spotted paper as Stachybotrys chartarum, which was observed to grow significantly in mineral salt medium supplemented with cellulose as the sole nutrient source; growth was shown in 10% NaCl. Two isolates from light red-spotted paper were related to Streptomyces sp. and Myxotrichum sp., respectively. These isolates generated red pigments in the mycelia and on the culture plates. Penicillium-related isolates were dominant in the sample tested, and they showed a higher level of NaCl tolerance. From the results of our on-site investigations, a unique discoloration, mainly black- and light red-spotted alterations caused by microbes, was observed on many paper-based objects that had been left wet for several months. The adhesive tape method applied to the black-spotted and red-spotted areas on damaged documents, Stachybotrys, Chaetomium and Cladosporium, and Actinomycetales bacterium were observed, respectively. With regard to the discoloration found on tsunami-affected paper-based objects, Stachybotrys and Streptomyces sp. seem to be responsible for the black- and red-spotted paper alterations, respectively.