An extremely haloalkaliphilic archaeon, strain AD2(T), was isolated from Aiding salt lake in Xin-Jiang, China. Strain AD2(T) required at least 12 % NaCl for growth. MgCl(2) was not required. The isolate was able to grow over a pH range of 8.0-10.0 and temperature range of 20-55 degrees C, with optimal growth at pH 8.7-9.2 and 44-47 degrees C. The major polar lipids of strain AD2(T) were phosphatidylglycerol and phosphatidylglycerol phosphate methyl ester; glycolipids were not detected. Analysis of its 16S rRNA gene sequence indicated that strain AD2(T) was phylogenetically related to members of the genus Natronorubrum, with sequence similarities to the type strains of Natronorubrum bangense, Natronorubrum tibetense and Natronorubrum aibiense of 97.1, 95.9 and 96.1 %, respectively. The G+C content of its DNA was 60.9 mol% (T(m)). Levels of DNA-DNA relatedness between strain AD2(T) and the type strains of Nrr. bangense, Nrr. tibetense and Nrr. aibiense were 49, 38 and 41 %, respectively. It was concluded that strain AD2(T) represents a novel species of the genus Natronorubrum, for which the name Natronorubrum sulfidifaciens sp. nov. is proposed. The type strain is AD2(T) (=CGMCC 1.6307(T)=JCM 14089(T)).