A thermophilic H(2)-producing bacterial strain was isolated from a biohydrogen reactor fed with palm oil mill effluent (POME) and identified as Thermoanaerobacterium thermosaccharolyticum using 16S rRNA gene analysis. The isolated bacterium, designated as T thermosaccharolyticum PSU-2, showed a high yield and production rate of H(2). Temperature optimum, pH optimum and substrate utilization for H(2) production were investigated in batch conditions. All of tested substrate was utilized for H(2) production, while sucrose, xylose and starch were the preferred substrates. The strain produced H(2) within a wide range of pH (4.5-8) and temperature (45-7 degrees C), with the optimal temperature 60 degrees C and optimal initial pH about 6.25. Maximum of H(2) production rate was registered from hour 8 to hour 16 in late exponential phase. The H(2) production was drastically reduced in a prolonged fermentation (24 h) and stopped at pH 4.5 due to the accumulation of organic acids. The maximum H(2) production yield and rate at sucrose concentration of 20 gl(-1), pH 6.25 and temperature 60 degrees C were 2.53 mol H(2) mol(-1) hexose and 12.12 mmol H(2) l(-1) h(-1), respectively. Organic nitrogen amended medium improved the H(2) production with 68% compared to inorganic nitrogen amended medium. The strain performed ethanol-acetate type fermentation in inorganic nitrogen amended medium, while it performed butyrate-acetate type fermentation in organic nitrogen amended medium. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.