I. A. IVANOVA and D. Y. POPOVA
University of Sofia “St. Kliment Ohridski”, Faculty of Biology, BG – 1164 Sofia, Bulgaria
IVANOVA, I. A. and D. Y. POPOVA, 2014. Pigmented yeasts survived 20 kGy gamma irradiation. Bulg. J. Agric. Sci., Supplement 1: 31–36
The cultural heritage deposited in museums, galleries, castles, libraries and private collections is subject to devastation caused by insects, bacteria and fungi. It is beyond the capacity of the small number of restorers, conservation workers and private collectors to combat those hazards using the classic methods. For that reason a radiation laboratory at the Sopharma JSC, Bulgaria, was used to study the biocidic effects of ionising radiation emitted by radioactive isotope of cobalt. That technique is particularly useful for books, as it is highly effective for the entire volume of paper under attack, and as it does not use any chemicals, it does not harm the fi nishes of the objects treated – binding, book cover, leather, etc. The biocide effects of the applied irradiation on the microorganisms populations on paper were estimated with classic method using cultivation in different nutrient media before and after the irradiation. The obtained results showed signifi cant decrease of the total number of microorganisms in all the paper samples after the lowest applied irradiation dose – 4 kGy. Only several heterotrophic bacteria, fungi and oligotrophic microorganisms survived this dose. Similar data were obtained after 10 kGy. Irradiation with 20 kGy led to highest degree of disinfectation of the papers, only single mixed culture of bacilli and yeast survived such dose. This is the fi rst report about the such kind of irradiated isolate presenting an association of yeasts and bacilli.
The present study showed that the gamma-irradiation of 4 kGy can be successfully applied for effi cient disinfection of the library archives, if higher dose is to be avoided to prevent structural changes of the paper like depolymerization of the cellulose, decrease of their mechanical strength etc. Further studies on the identifi cation of the microbial isolates have to be performed.