A Bacillus sp., designated as strain MN-003, was isolated as the dominant cultivatable naphthalene-degrading organism from oil-contaminated tropical marine sediments. Strain MN-003 is strictly aerobic, rod-shaped, Gram-positive, catalase positive, oxidase negative, and forms endospores. Strain MN-003 grew at salinities ranging from 0.28 to 7.00% and temperatures ranging from 15 to 41degreesC. Phylogenetic analyses reveal that strain MN-003 is most similar to Bacillus sp. VAN14, with a 165 rRNA sequence identity of 97.9%. Based on taxonomic and 16S rRNA data, strain MN-003 was named Bacillus naphthovorans sp. nov. When grown with naphthalene as sole carbon source, strain MN-003 had a maximal specific growth rate (mu(max)) of 0.32+/-0.03 h(-1), and a half-saturation constant (K-s) of 22.3+/-4.2 muM. A batch study of the tropical marine sediments enriched with naphthalene showed that cells of the Bacillus genus grew to become dominant members of the microbial community. The bacilli comprised 39.5+/-6.5% of the microbial fraction after 20 days of enrichment.