To analyze metabolically active thermophilic bacteria, a high-temperature direct viable count (HT-DVC) method was developed and applied to sewage sludge compost made by a hyperthermal composting method. When the HT-DVC method was conducted at 60 ℃ and 80 ℃, maximum numbers of 23.3×108 and 2.62×108 cells/(g of dry sample) of elongated cells (length >4 μm), respectively, were detected. These results indicate that the HT-DVC method can be used to enumerate even metabolically active extreme thermophiles. Strain TH, a Gram-negative, spore-forming, and extremely thermophilic bacterium, which showed growth at 55-78 ℃, was isolated from the sewage sludge compost. Strain TH is closely related to Caldaterra satsumae YMO81. The HT-DVC method could detect strain TH inoculated into sewage sludge compost with autoclaving, but could not selectively detect the strain inoculated into the compost without autoclaving.
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