We describe a new caldoactive bacterium, Dictyoglomus thermophilum, which was isolated from a slightly alkaline hot spring. This organism is a nonsporeforming, nonmotile, obligately anaerobic rod-shaped bacterium that stains gram negative and occurs singly, in pairs, in filaments, in bundles, and as spherical bodies. The cell surface structure is of the complex gram-negative type. Large spherical bodies are formed by associations of separate rods in numbers ranging from a few to perhaps as many as 100; these spherical bodies are surrounded by common outer wall membrane. The temperature range for growth is between 50 and 80°C, with optimum growth at 78°C; the pH range for growth is between 5.9 and 8.3. The doubling time at 73°C and pH 7.2 is about 2.5 h. Growth is inhibited by streptomycin, tetracycline, neomycin, chloramphenicol, vancomycin, tunicamycin, and sodium dodecyl sulfate. The deoxyribonucleic acid base composition is 29 mol % guanosine plus cytosine. The type strain is strain ATCC 35947.Bacteria that grow at temperatures over 70°C are called caldoactive or extremely thermophilic (10, 18). It has been pointed out that volcanic environments such as hot springs may be more conducive for the growth of anaerobes than for the growth of aerobes because of the low solubility of 02 at high temperatures, the presence of H2S, and the high organic content associated with decomposing biomass (20). Extremely thermophilic, anaerobic chemoorganotrophs, including Thermoanaerobium brockii (20), Thermoanaerobacter ethanolicus (19), and Thermobacteroides acetoethylicus (3), have been isolated from hot springs at Yellowstone National Park and from other volcanic environments during the past several years (6,17,(21)(22)(23). We examined hot springs in Japan with the hope of isolating thermophilic anaerobes which may be potentially useful for industrial purposes. One anaerobic isolate is described in this paper. This organism is an extremely thermophilic, nonsporulating, chemoorganotrophic, rod-shaped bacterium which forms large spherical bodies consisting of a few to perhaps 100 separate cells. The properties of this strain do not fit those of any previously described genus.
MATERIALS AND METHODSChemicals. All chemicals were reagent grade. Tetracycline and streptomycin sulfate were obtained from Takeda Chemical Industries Ltd., Osaka, Japan. Actinomycin D, Dcycloserine, ampicillin, and vancomycin were obtained from Sigma Chemical Co., St. Louis, Mo, penicillin G was obtained from Meiji Confectionary Co. Ltd., Kawasaki, Japan, neomycin was obtained from Boehringer Mannheim, Mannheim, Federal Republic of Germany, and chloramphenicol was obtained from Sankyo Co. Ltd., Tokyo, Japan. Tunicamycin was a gift from Akira Takatsuki, University of Tokyo, Tokyo, Japan. Lysozyme (6x crystallized) was purchased from Seikagaku Kogyo Co. Ltd., Tokyo, Japan.
* Corresponding author. t Present address: Alcohol Production Head Office, New EnergyDevelopment Organization, Toranomon 3-5-1, Minato-ku, Tokyo 105, Japan.Polypeptone, yeast extract, a...