Abstract
In order to investigate the mechanism of microbial growth at elevated temperatures, it was tried to isolate different thermophilic microorganisms from wide origins, such as soils, composts, manure piles and hot spring waters. As the result, 5 strains of extremely thermophilic bacteria, the maximum, the optimum and the minimum temperatures for growth of which were 80, 70_??_75, and 40°C, respectively, were isolated from Izu-Atagawa hot spring and Beppu hot springs. These bacteria were gram-negative, yellow-pigmented, non-motile and non-sporulating rods of 0.5_??_0.7μ in diameter and 2_??_5μ in length. They were heterotrophs requiring several amino acids (such as glutamate, aspartate, et al.) and vitamins (such as biotin, folic acid and p-aminobenzoic acid) and grew well at neutral to slight alkali pH. The content of GC pairs of DNAs from the 5 strains was 69_??_70%, and this seemed to be one of the highest values in bacteria so far known. Among the 5 strains, strain AT-62 was named as Thermus flavus sp. _??_ AT-62 from its morphological and physiological characteristics. Comparison between Thermus flavus and other extremely thermophilic bacteria as Thermos aquaticus and Flavobacterium thermophihum is described and discussed in reference to classification of extremely thermophilic bacteria.
