The degradation of methanethiol (MT) at 30 degrees C under saline-alkaline (pH 8-10, 0.5 M Na+) conditions was studied in a lab-scale Upflow Anaerobic Sludge Blanket (UASB) reactor inoculated with estuarine sediment from the Wadden Sea (The Netherlands). At a sodium concentration of 0.5 M and a pH between 8 and 9 complete MT degradation to sulfide, methane and carbon dioxide was possible at a maximum loading rate of 22 mmol MT L-1 day(-1) and a hydraulic retention time of 6 h. The presence of yeast extract (100 mg/L) in the medium was essential for complete MT degradation. 16S rRNA based DGGE and sequence analysis revealed that species related to the genera Methanolobus and Methanosarcina dominated the archaeal community in the reactor sludge. Their relative abundance fluctuated in time, possibly as a result of the changing operational conditions in the reactor. The most dominant MT-degrading archaeon was enriched from the reactor and obtained in pure culture. This strain WR1, which was most closely related to Methanolobus taylorii, degraded MT, dimethyl sulfide (DMS), methanol and trimethylamine. Its optimal growth conditions were 0.2 M NaCl, 30 degrees C and pH 8.4. In batch and reactor experiments operated at pH 10, MT was not degraded. (C) 2008 Elsevier Ltd. All rights reserved.