Occurrence of Extreme Thermophiles, Thermaerobacter spp., in Sewage Sludge

We isolated an extreme thermophilic bacterium strain SS, which grew between 55 and 82°C (optimum 70°C), from sewage sludge in Kagoshima City, Japan. Morphological and physiological properties, as well as 16S rRNA gene sequence indicated that strain SS belongs to the genus Thermaerobacter. To confirm the distribution of Thermaerobacter spp. in sewage sludge, genus-specific detection by nested PCR of 16S rRNA gene was performed. As a result, the existence of Thermaerobacter spp. in six sewage sludge samples including composted sludge was demonstrated by sequencing of the nested PCR products. However, enrichment cultures with sewage sludge were needed to detect the target products, indicating that population of Thermaerobacter spp. may be significantly low. As far as we know, this is the first report on occurrence of extreme thermophilic bacteria in a municipal wastewater treatment process under mesophilic condition.