Methylocaldum marinum sp. nov., a thermotolerant, methane-oxidizing bacterium isolated from marine sediments, and emended description of the genus Methylocaldum

Abstract

An aerobic, methane-oxidizing bacterium (strain S8T) was isolated from marine sediments in Kagoshima Bay, Japan. Phylogenetic analysis based on 16S rRNA gene sequences indicated that this strain is closely related to members of the genus Methylocaldum (97.6–97.9 % similarity) within the class Gammaproteobacteria . Strain S8T was a Gram-staining-negative, non-motile, coccoid or short rod-shaped organism. The temperature range for growth of strain S8T was 20–47 °C (optimum growth at 36 °C). It required NaCl (>0.5 %), tolerated up to 5 % NaCl and utilized methane and methanol. The major cellular fatty acid and major respiratory quinone were C16 : 0 and 18-methylene ubiquinone 8, respectively. The DNA G+C content was 59.7 mol%. Strain S8T possessed mmoX, which encodes soluble methane monooxygenase, as well as pmoA, which encodes the particulate methane monooxygenase. On the basis of this morphological, physiological, biochemical and genetic information, the first marine species in the genus Methylocaldum is proposed, with the name Methylocaldum marinum sp. nov. The type strain is S8T ( = NBRC 109686T = DSM 27392T). An emended description of the genus Methylocaldum is also provided.