Summary auto-generated
Researchers isolated a novel anaerobic, thermophilic bacterium designated strain JMT from a submarine hydrothermal vent in the Okinawa Trough at 1395 m depth. The organism grows chemolithotrophically on carbon monoxide (CO), converting it to equimolar quantities of hydrogen and carbon dioxide according to the reaction: CO + H2O → CO2 + H2. It can also grow organotrophically on various substrates including peptone, yeast extract, glucose, and galactose, producing acetate, hydrogen, and carbon dioxide. Cells are long, thin, non-motile branching rods with Gram-positive cell walls surrounded by an S-layer. The isolate grows optimally at 70°C (range 50-80°C) and pH 6.8-7.2, with a generation time of 7.1 hours under optimal conditions. Phylogenetic analysis of 16S rRNA sequences shows the organism clusters within the Thermoanaerobacter group but represents a distinct branch with sufficient differences to warrant designation as a new genus. Based on morphological, physiological, and genetic characteristics, researchers propose the new genus Carboxydobrachium with the type species Carboxydobrachium pacificum, representing the first pure culture of an anaerobic marine CO-utilizing hydrogen-producing thermophile.
Key findings
- Strain JMT oxidizes CO to CO2 and H2 in equimolar ratios, making it only the third known thermophilic bacterium capable of this anaerobic lithotrophic metabolism
- It is the first marine CO-utilizing thermophilic bacterium isolated in pure culture, demonstrating obligate seawater requirements unlike previously known CO-oxidizing thermophiles from freshwater vents
- The organism exhibits metabolic versatility by growing both chemolithotrophically on CO and organotrophically on fermentable substrates like glucose and galactose
- 16S rRNA sequence analysis shows 92.3-93.5% similarity to Thermoanaerobacter species but lacks characteristic secondary structures and signature nucleotides, supporting its classification as a separate genus
- The bacterium was recovered from a deep-sea hydrothermal environment at 1395 m depth in the Okinawa Trough, expanding knowledge of microbial diversity in marine vent ecosystems
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Abstract
A new anaerobic, thermophilic, CO-utilizing marine bacterium, strain JM(T), was isolated from a submarine hot vent in Okinawa Trough. Cells of strain JM(T) were non-motile thin straight rods, sometimes branching, with a cell wall of the Gram-positive type, surrounded with an S-layer. Chains of three to five cells were often observed. The isolate grew chemolithotrophically on CO, producing equimolar quantities of H(2) and CO(2) (according to the equation CO+H(2)O -> CO(2)+H(2)) and organotrophically on peptone, yeast extract, starch, cellobiose, glucose, galactose, fructose and pyruvate, producing H(2), acetate and CO(2). Growth was observed from 50 to 80 degrees C with an optimum at 70 degrees C. The optimum pH was 6.8--7.1. The optimum concentration of sea salts in the medium was 20.5--25.5 g l(-1). The generation time under optimal conditions was 7.1 h. The DNA G+C content was 33 mol%. Growth of isolate JM(T) was not inhibited by penicillin, but ampicillin, streptomycin, kanamycin and neomycin completely inhibited growth. The results of 16S rDNA sequence analysis revealed that strain JM(T) belongs to the Thermoanaerobacter phylogenetic group within the Bacillus--Clostridium subphylum of Gram-positive bacteria but represents a separate branch of this group. On the basis of morphological and physiological features and phylogenetic data, this isolate should be assigned to a new genus, for which the name Carboxydobrachium is proposed. The type species is Carboxydobrachium pacificum; the type strain is JM(T) (=DSM 12653(T)).