Tepidicaulis marinus gen. nov., sp nov., a marine bacterium that reduces nitrate to nitrous oxide under strictly microaerobic conditions

A moderately thermophilic, aerobic, stalked bacterium (strain MA2(T)) was isolated from marine sediments in Kagoshima Bay, Japan. Phylogenetic analysis of 16S rRNA gene sequences indicated that strain MA2(T) was most closely related to the genera Rhodobium, Parvibaculum, and Rhodoligotrophos (92-93% similarity) within the class Alphaproteobacteria. Strain MA2(T) was a Gram-stain-negative and stalked dimorphic bacteria. The temperature range for growth was 16 48 degrees C (optimum growth at 42 degrees C). This strain required yeast extract and NaCI (>1%, w/v) for growth, tolerated up to 11% (w/v) NaCl, and was capable of utilizing various carbon sources. The major cellular fatty acid and major respiratory quinone were C-18:1 omega 7c and ubiquinone-10, respectively. The DNA G + C content was 60.7 mol%. Strain MA2(T) performed denitrification and produced N2O from nitrate under strictly microaerobic conditions. Strain MA2(T) possessed periplasmic nitrate reductase (Nap) genes but not membrane-bound nitrate reductase (Nar) genes. On the basis of this morphological, physiological, biochemical and genetic information a novel genus and species, Tepidicaulis marinus gen. nov., sp. nov., are proposed, with MA2(T) (=NBRC 109643(T)=DSM 27167(T)) as the type strain of the species.