Analytical pyrolysis evidences the presence of granaticins in the violet stains of a Roman tomb

•The walls of the Circular Mausoleum tomb, Spain, are deteriorated by microorganisms.•Violet stains are produced by a strain of Streptomyces isolated from the walls.•The Streptomyces strain produces granaticin A in the laboratory.•Analytical pyrolysis shows the presence of granaticin A in the violet-colored walls.

The walls of the Circular Mausoleum tomb (Roman Necropolis of Carmona, Spain) exhibit an important number of violet stains of unknown origin. Analytical pyrolysis detected in the tomb walls granaticin A, a violet pigment with an isobenzochromanequinone structure, as well as in the extracts of two bacterial strains isolated from the walls. The bacterium was tentatively identified as Streptomyces sp. High performance liquid chromatography confirmed that this Streptomyces synthesized as major pigments dihydrogranaticin A, granaticin A and granaticin B.