Two Gram-staining-negative, rod-shaped and non-motile strains, designated CL-CB221T and CL-CB467, were isolated from a Synechococcus culture derived from tropical surface water of the Pacific Ocean. The 16S rRNA gene sequences of the two strains were identical, and it was found that they belonged to the class Gammaproteobacteria, with Spongiibacter marinus HAL40bT as their closest relative (similarity of 96.3%). Both strains grew optimally at 30-35 degrees C and pH 7-8 in the presence of 3-4% (w/v) NaCl. The major cellular fatty acids were C18:1omega7c, C17:1omega8c, C16:0 and summed feature 3 (C16:1omega7c and/or iso-C15:0 2-OH). The genomic DNA G+C contents were 57.7 and 57.8 mol%, respectively. DNA-DNA hybridization experiments revealed high values (97+/-2%) for relatedness between strains CL-CB221T and CL-CB467, which suggested that these two strains belong to a single species. Based on the phylogenetic, chemotaxonomic and phenotypic data presented, it is proposed that strains CL-CB221T and CL-CB467 represent a novel species of the genus Spongiibacter, for which the name Spongiibacter tropicus sp. nov. is proposed. The type strain is CL-CB221T (=KCCM 90065T=DSM 19543T).