Microbial growths causing discoloration on the Roman wall paintings of the Servilia tomb at the necropolis of Carmona (Spain) and the medieval wall paintings of the Saint-Catherine chapel at Castle Herberstein (Austria) were investigated and from four different samples, a group of ten strains with similar characteristics was isolated. The isolates were characterized in a polyphasic taxonomic study, including 16S rDNA sequence analysis, (GTG)5-PCR genomic fingerprinting, DNA-DNA hybridization, DNA base ratio, fatty acid analysis, morphological and biochemical characterization. The data obtained attribute the isolates to a novel species of the genus Bacillus, for which the name Bacillus decolorationis sp. nov. is proposed. The type strain is strain LMG 19507T (=DSM 14890T).