A Gram-negative bacterium, designated LA33B(T), was isolated from water collected from a hypersaline lake on uninhabited Laysan Atoll in the Northwestern Hawaiian Islands. Cells of strain LA33B(T) are motile, straight rods that grow between 4 and 45 degrees C and in media containing 1-17.5% (w/v) NaCl. The strain oxidizes carbohydrates, nucleosides, amino acids and organic acids presented as sole carbon sources and constitutive lipolytic and proteolytic enzymes are expressed. Over 75% of the fatty acid pool is cis-11-octadecenoic acid (18:1omega7c). Comparative sequence analysis of the 16S rRNA gene indicates that the strain forms a new lineage in the alpha-2 subclass of the Proteobacteria, with the closest recognized strains being Stappia aggregata NCIMB 2208T and Roseibium denhamense JCM 10543T, with which it shares 94-95% sequence similarity. Strain LA33B(T) differs phenotypically from extant Stappia and Roseibium species, however, in that it is a moderate thermophile, it requires NaCl and tolerates higher NaCl concentrations and it does not express beta-galactosidase or oxidize glycerol. On the basis of genotypic data and phenotypic characteristics, we propose that strain LA33B(T) does not belong to the genera Stappia or Roseibium and that it represents the type species of a new genus, Nesiotobacter. Strain LA33B(T) (= ATCC BAA-994T = CIP 108449T) is proposed as the type strain of the type species of this genus, with the name Nesiotobacter exalbescens gen. nov., sp. nov.