A novel thermophilic actinomycete, designated AG2-7 T , was isolated from mushroom residue compost in Guangxi University, Nanning, China. The strain grew optimally at 45-60 6C, at pH 7.0 and with 0-3.0 % (w/v) NaCl. Vegetative mycelia were branched and whitish to pale yellow without fragmentation. Aerial mycelium was abundant, whitish and differentiated into long chains of spores, with a membranous structure or tunica partially covering the surface of aerial hyphae. The non-motile spores were oval in shape with a ridged surface. Strain T contained mesodiaminopimelic acid as the diagnostic diamino acid, and the whole-cell sugars were galactose and ribose. Major fatty acids were iso-C 16 : 0 (27.51 %), iso-C 17 : 0 (10.47 %) and anteiso-C 17 : 0 (12.01 %). MK-9(H 4 ) was the predominant menaquinone. The polar phospholipids were diphosphatidylglycerol, ninhydrin-positive glycophospholipid, phosphatidylinositol, phosphatidylinositol mannoside, phosphatidylethanolamine, phosphatidylmethylethanolamine, an unknown phospholipid and unknown glucosamine-containing phospholipids. The G+C content of the genomic DNA was 63.6 mol%. 16S rRNA gene sequence analysis showed that the organism belonged to the family Pseudonocardiaceae, suborder Pseudonocardineae and showed more than 5 % divergence from other members of the family. Based on the phenotypic and phylogenetic data, strain AG2-7 T represents a novel species of a new genus in the family Pseudonocardiaceae, for which the name Thermotunica guangxiensis gen. nov., sp. nov. is proposed. The type strain of the type species is AG2-7 T (5ATCC BAA-2499 T 5CGMCC T ).The family Pseudonocardiaceae was established by Embley et al. (1988) (Hayakawa & Nonomura, 1987) and incubation at 50 u C in the dark for 3 days under aerobic conditions. The isolate was maintained on modified Sauton's agar (Mordarska et al., 1972) at 4 u C and as suspensions of mycelial fragments in 20 % (v/v) glycerol at 220 u C.Cultural characteristics of strain AG2-7 T were tested on ISP2, ISP3, ISP4, ISP5, ISP6 and ISP7 media (Shirling & Gottlieb, 1966), Gause's asparagine agar (Gause et al., 1983), Bennett's agar (Jones, 1949), Czapek solution agar, potato agar (Waksman, 1961), Sauton's agar, HV medium and water agar (15.0 g agar, 1 l tap water) after incubation for 7 days at 50 u C. Morphological characteristics were observed under a light microscope (80i; Nikon) and a scanning electron microscope (VEGA3 SBU; TESCAN) after incubation for 3-7 days on HV media at 50 u C. Growth temperature and resistance to NaCl was tested on modified Bennett's agar at 4, 16, 28, 37, 40, 45, 50, 55, 60, 65 and 70 u C and observed after 7 and 14 days. Tolerance to NaCl between 0 and 15 % (at intervals of 1 %) was read after 3 and 7 days at 50 u C. The pH range and the optimum pH for growth were examined on Sauton's agar with the pH range between pH 4.0 and 11.0 (in intervals of 1.0 pH unit) using the following buffer systems: for pH 4.0-6.0, 0.1 M citric acid/0.1 M sodium citrate; pH 7.0-9.0, 0.1 M Tris/0.1 M HCl; pH 9.5-10.0, 0...