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An orange-black, Gram-positive, aerobic and gamma-ray resistant actinobacterium was isolated from the ruins of a Roman aqueduct located in Northern Tunisia. The optimal growth for the strain was found to be at 25-35 A degrees C and at pH 6.0-9.5. Chemotaxonomic and molecular characteristics of the isolate matched those described for members of the genus Geodermatophilus. The peptidoglycan was found to contain meso-diaminopimelic acid as diagnostic diaminoacid. The main polar lipids were identified as phosphatidylcholine, diphosphatidylglycerol, phosphatidylinositol, phosphatidylethanolamine, an unidentified glycolipid and an unidentified aminophospholipid; MK-9(H-4) was found to be the dominant menaquinone and galactose was detected as the diagnostic sugar, with glucose, ribose and mannose also present. The major cellular fatty acids were identified as branched-chain saturated acids iso-C-16:0, iso-C-15:0 and iso-H-C-16:0. The 16S rRNA gene showed 95.4-99.6 % sequence identity with the type strains of the genus Geodermatophilus. DNA-DNA relatedness values with closely related species were 39.9 +/- A 4.9, 33.9 +/- A 1.9, 27.0 +/- A 2.5 and 13.2 +/- A 1.35 % with Geodermatophilus amargosae, G. normandii, G. saharensis and G. tzadiensis respectively. Based on phenotypic results and 16S rRNA gene sequence analysis, strain BMG801(T) (=DSM 46834(T) = CECT 8822(T)) is proposed to represent the type strain of a novel species, Geodermatophilus aquaeductus sp. nov.