A Gram-positive, rod-shaped, non-endospore-forming, mycelium-forming actinobacterium (04-St-002 T ) was isolated from the wall of an indoor environment colonized with moulds. On the basis of 16S rRNA gene sequence similarity studies, strain 04-St-002 T was shown to belong to the family Pseudonocardiaceae, and to be most closely related to Pseudonocardia antarctica (99.2 %) and Pseudonocardia alni (99.1 %). The major menaquinones were MK-8(H 4 ) and MK-8(H 2 ), the phospholipid type was PIII, and the polar lipid profile consisted of the major lipids diphosphatidylglycerol, phosphatidylmonomethylethanolamine and phosphatidylcholine. Moderate amounts of phosphatidylglycerol and an unknown polar lipid, L1, small or trace amounts of phosphatidylinositol, phosphatidylinositol-mannoside, three unknown lipids, two unknown phospholipids and four unknown glycolipids were also detected. The major fatty acids iso-C 16 : 0 , iso-C 16 : 1 , C 16 : 0 and C 16 : 1 v7c supported the affiliation of strain 04-St-002 T to the genus Pseudonocardia. The results of DNA-DNA hybridization, and physiological and biochemical tests allowed genotypic and phenotypic differentiation of strain 04-St-002 T from the two most closely related species, P. alni and P. antarctica. Strain 04-St-002 T represents a novel species, for which the name Pseudonocardia parietis sp. nov. is proposed. The type strain is 04-St-002 T (5DSM 45256 T 5CCM 7582 T ).The genus Pseudonocardia, originally proposed by Henssen (1957) for nocardioform actinomycetes that lack mycolate and have a type IV cell wall, reflected by the presence of meso-diaminopimelic acid and the sugars arabinose and galactose (Lechevalier & Lechevalier, 1980), comprises 28 species at the time of writing (Gu et al., 2006; Huang et al., 2002;Lee et al., 2000Lee et al., , 2001Lee et al., , 2002Lee et al., , 2004 Kämpfer & Kroppenstedt, 2004;Liu et al., 2006; Mahendra & AlvarezCohen, 2005;Qin et al., 2008).Strain 04-St-002 T was isolated from a wall colonized with moulds. After extraction of 1 g material sample for 15 min in 10 ml 0.9 % NaCl solution containing 0.01 % (v/v) Tween 80 and dilution on M79 agar (containing 10 g glucose, 10 g Bacto peptone, 2 g casein hydrolysate, 2 g yeast extract, 6 g NaCl, 15 g agar) for 2 weeks at 28 u C, the strain was maintained on M79 at 28 u C and showed a brown-coloured substrate mycelium. After a few days, a white aerial mycelium formed.Morphological properties, Gram-staining and cell morphology were observed by phase-contrast microscopy as described by Kämpfer & Kroppenstedt (2004). DNA isolation was performed with a commercial DNA extraction kit (GenElute Plant Genomic DNA kit; Sigma). Initially, the sample was prepared by a 1 min bead-beating step with 1 g 0.1 diameter Zirconia beads.Multiple sequence alignment and analysis of the data were performed using the software package MEGA version 4 (Tamura et al., 2007). Genetic distance calculations (distance options according to the Kimura two-parameter model), and clustering with the neighbour-joining (Fig. 1...