Cultivation characteristics of denitrification by thermophilic Geobacillus sp. strain TDN01

Nine thermophilic denitrification bacteria were isolated from field soil, mud, and spa samples. The alignment of 16S rDNA showed that all were identical to the genus Geobacillus. Two of the bacteria produced N₂O and N₂ gas and the other seven strains produced N₂ gas from nitrate. We examined the growth substrates for Geobacillus TDN01 and determined that sodium succinate, pyruvate, formate, acetate, glycerol, glucose, sucrose, and cellobiose well supported growth of the isolate. Growth occurred under the following concentration of NO₃^- and phosphate: 10-60 mmol/L, and 0.1-50 mmol/L, respectively. Thermophilic TDN01 grown on sodium succinate accumulated nitrite. A time course of denitrification by Geobacillus TDN01 in a jar fermentor revealed that maintaining a pH of around 7 is important for denitrification without accumulating NO₂. The NO₃^- and NO₂^- consumption ratios of Geobacillus were 44-75 and 9-41 times higher, respectively, than those of Pseudomonas stutzeri JCM 5965^T.