Resolving the mummification enigma of Baroness Zsófia Serédy-Andrássy (1663–1710?) entombed in Krásna Hôrka Castle, Slovakia

Microbiological investigations of skin, hair, and intra-corporeal tissue of the mummified body of Zsófia Serédy-Andrássy, who had been laid to rest in a glass coffin in the Krásna Hôrka Castle in southeastern Slovakia, revealed necrobiome dominated by the phylum Firmicutes followed by representatives of the phyla Actinobacteria and Proteobacteria . Optically visible bright-to-yellow mineral precipitates on the skin and organs are dominated by potassium sulphate (the mineral arcanite), with a minor admixture of chlorides (probably halite). Only a very rare calcium carbonate has been identified on the hair surface. The high concentrations of potassium in both tissue and hair, together with the 34 S-rich isotope compositions of keratin sulphur (δ 34 S = 11.6–11.7‰ CDT) and skin leachate (δ 34 S = 7.1–8.5‰ CDT), suggest either the excessive use of K 2 SO 4 during medical treatment or intentional embalming – the first such documented case in Europe for the period. Biogenic microbial or fungal origin of essentially pure K 2 SO 4 is highly unlikely. The high residual levels of non-excreted salts, combined with the dry microclimatic environment of church crypt, resulted in the body mummification and crystallization of potassium sulphate on the skin surface and internal organs. The commonly accepted conjecture regarding the natural mummification of Zsófia's corpse, which is believed to be caused by calcium hydrogen carbonate or calcium bicarbonate-rich drip water and subsequent desiccation, should be rejected. • K 2 SO 4 (Arcanite) occurs on the mummy of Baroness Zsófia Serédy-Andrássy. • Necrobiome consists of Firmicutes , Actino- and Proteobacteria , fungi and yeasts. • Isotope ratio 34 S/ 32 S in K 2 SO 4 inconsistent with the biogenic origin. • Increased K content in hair indicates intoxication or specific embalming procedure. • Assumption about mineralized drip water as mummification agent is invalid.