Rhodothermus marinus, gen. nov., sp. nov., a Thermophilic, Halophilic Bacterium from Submarine Hot Springs in Iceland

1 Institute of Biology, University of Iceland, IS-108 Reykjavik, Iceland 2 Lehrstuhl für Mikrobiologie, Universität Regensburg, D-8400 Regensburg, FRG ABSTRACT SUMMARY: Thermophilic, reddish-coloured heterotrophic bacteria different from Thermus were isolated from submarine alkaline hot springs in Iceland. The bacteria were obligately aerobic, moderately halophilic, Gram-negative rods, about 0.5 µm in diameter and 2-2.5 µm long. Neither spores, flagella nor lipid granules were observed, but a slime capsule was formed on carbohydrate-rich medium. Optimum growth was at 65°C, pH 7.0, and at about 2% (w/v) NaCl. The bacteria were oxidase negative, catalase positive and contained a carotenoid pigment with the main absorbance peak at 476 nm and shoulders at 456 and 502 nm. The GC content of the DNA was about 64 mol%. Electron micrographs clearly showed an outer membrane, about 9 nm thick, and the cytoplasmic membrane together with the peptidoglycan layer was about 14 nm in thickness. The isolates were nutritionally different from Thermus. They utilized several common sugars but glutamate and aspartate were the only amino acids that most strains used. These bacteria are considered to represent a new genus which we name Rhodothermus , with the type species Rhodothermus marinus. Present address: Biotechnology Laboratory, Icelandic Technology Institute, IS-112 Reykjavik, Iceland.