A heterotrophic and thermotolerant marine bacterium, designated strain T5054, was isolated from a hot spring on the coast of Lutao, Taiwan. It was a strictly aerobic, Gram-negative rod. Cells grown in broth cultures were non-spore-forming and motile by means of one to several polar flagella. It seems that pilus-like structures were produced from both poles of the cells. Strain T5054 required Na+ for growth and exhibited optimal growth at about 45 degrees C, pH 7, and 3-5% NaCl. It contained iso-C15:0 as the most abundant fatty acid and ubiquinone-8 as the only isoprenoid quinone. Its genomic DNA G+C content was 63.5 mol%. The strain did not require vitamins or other organic growth factors, and it grew on glucose, mannitol, and a variety of organic acids and amino acids as sole carbon sources. Characterization data, together with the results of a 16S rDNA-based phylogenetic analysis, indicated that strain T5054 could be classified as a new species in the genus Marinobacter. The name Marinobacter lutaoensis sp. nov. is proposed for this new bacterium. The type strain is T5054 (CCRC 17087; JCM 11179).