Rhodothermus obamensis sp. nov., a Modern Lineage of Extremely Thermophilic Marine Bacteria

Abstract

A novel extremely thermophilic bacterium was isolated from a shallow marine hydrothermal vent environment (depth, 22 m) in Tachibana Bay, Nagasaki Prefecture, Japan. The cells of this organism were gramnegative rods. Growth occurred at temperatures between 50 and 85°C (optimum temperature, 80°C; doubling time at optimum temperature, 90 min), at pH 5.5 and 9.0 (optimum pH, 7.0), and in the presence of 1 and 5% NaCl (optimum NaCl concentration, 3%). The new isolate was an aerobic heterotroph which utilized the following compounds as sole energy and carbon sources: yeast extract, peptone, starch, casein, Casamino Acids, a variety of sugars, some carboxylic acids, and amino acids. As determined by a sequence analysis of the 16s rRNA, the new isolate belongs to the genus Rhodothermus and represents a modern lineage of extreme thermophiles within the domain Bacteria. On the basis of the physiological and molecular properties of the new isolate, we describe a new species, Rhodothermus obamensis. The type strain of R. obamensis is strain OKD7 (= JCM 9785).Over the last 10 years, a number of new genera and species of thermophilic organisms which are capable of growth at temperatures up to 80°C have been isolated. Most of these organisms belong to the domain Archaea (31), but there are a few genera, such as the genera Themus, Thennotoga, and Aquifex, which belong to the domain Bacteria (5, 10, 11). These thermophiles have distinct physiological differences; the members of the genus Themus are strictly aerobic heterotrophs, the members of the genus Thermotoga are strictly anaerobic heterotrophs, and the members of the genus Aquifex are microaerobic chemolithoautotrophs. On the basis of 16s rRNA analysis data, the genera Thennotoga and Aquifex represent the deepest phylogenetic branches in the domain Bacteria (7, 21). Moreover, the genus Thennus also branches deeply on the phylogenetic tree inferred from 16s rRNA sequences (21). These findings and the results of a phylogenetic study of the thermophilic genus Hydrogenobacter support the hypothesis that the ancestors of bacteria were thermophilic species (1,26).The members of the genus Rhodothemus, on the other hand, are marine thermophilic bacteria that have been isolated from sites in Iceland and the Azores (2, 20). Rhodothemus marinus is an aerobic heterotrophic bacterium that has an optimum growth temperature of 65°C and has been used in studies of genetic engineering of thermostable enzymes (28). A 16s rRNA analysis of this organism placed the genus Rhodothermus close to the root of the Flexibacter-Cytophaga-Bacteroides group with affinities to the green sulfur bacteria, fibrobacteria, and spirochetes (3). This phylogenetic position of the genus Rhodothennus differs from the phylogenetic positions of other thermophilic bacteria and suggests that there are thermophilic or extremely thermophilic bacteria which are distant from the universal root of life and that there was another origin of thermophily within the Bacteria (3).In this paper, we describe the isolation and cha...

A novel hydrogen oxidizer amidst the sulfur-oxidizing Thiomicrospira lineage

“…MJ medium was prepared as described before (Sako et al, 1996), without yeast extract and without trypticase peptone, but 10 ml of vitamin solution was added (Balch et al, 1979). A volume of 50 ml of medium was filled into 120 ml serum bottles closed with rubber stoppers and purged with a H 2 :CO 2 :O 2 (79:20:1) gas mixture (Westfalen AG, Mü nster, Germany).…”

Deferribacter desulfuricans sp. nov., a novel sulfur-, nitrate- and arsenate-reducing thermophile isolated from a deep-sea hydrothermal vent

“…MJNS medium consisted of (l 21 MJ synthetic sea water): 1 ml vitamin solution (Balch et al, 1979), 50 mg sodium selenite, 30 mg sodium tungstate, 1 mg resazurin, 10 mM NaNO 3 , 3 % (w/v) elemental sulfur, 20 g NaHCO 3 and 0?5 g Na 2 S.9H 2 O (Sako et al, 1996;Takai et al, 1999). To prepare the supplemented medium, sodium selenite, sodium tungstate, resazurin, yeast extract (1 g) and tryptone (1 g) were dissolved in 1 l MJ synthetic sea water and the pH of the medium was adjusted to around 7?0 with NaOH before autoclaving.…”

“…Each of the sample sections (approx. 10 g each) was suspended in 20 ml sterilized MJ synthetic sea water (Sako et al, 1996;Takai et al, 1999) containing 0?05 % (w/v) sodium sulfide in a 100-ml glass bottle (Schott Glaswerke) tightly sealed with a butyl rubber cap under a gas phase of 100 % N 2 (100 kPa). These suspended portions of the samples were inoculated (0?1 % volume of the medium) with MJNS medium (described below) supplemented with 0?1 % (w/v) yeast extract and 0?1 % (w/v) tryptone under a gas phase of 80 % H 2 and 20 % CO 2 (300 kPa).…”

Balneola vulgaris gen. nov., sp. nov., a member of the phylum Bacteroidetes from the north-western Mediterranean Sea

“…This family is remarkable as all its members described to date exhibit characteristics that are regarded as extremophilic. Species of the genera Rhodothermus (Alfredsson et al, 1988;Sako et al, 1996) and Thermonema (Hudson et al, 1989;Tenreiro et al, 1997) are thermophilic and have optimal growth temperatures between 60 and 80 u C. Isolates of the genus Salinibacter are extremely halophilic and require at least 150 g salt l 21 for growth. In this paper, a novel strain of the family Crenotrichaceae, isolated from the north-western Mediterranean Sea, is described; this strain represents the first member of this family that does not exhibit the extreme characteristics that are found in other members of the family.…”