Extremely thermophilic gram-negative bacteria from hot tap water.

Two strains of heterotrophic, non-motile, Gram-negative extreme thermophiles have been isolated from hot tap water. These strains (NH and DI) have been characterized and compared with strains of genus Thermus. Few of the single organic compounds tested supported growth in the presence of ammonium salts, and, like Thermus strains, growth on undefined media was restricted to dilute tryptone-yeast extract-mineral salt solutions. Nutrients agar and similar common laboratory media did not support growth. The growth rate was similar to that of Thermus strains, as was the unusual pattern of antibiotic resistance. Mean base composition of NH was 61-4% guanine plus cytosine (G+C), and DI was 62-0 to 62-2% G+C, which are several per cent lower than the G+C contents of other strains so far described.