Four strains of acetic acid bacteria were isolated from flowers collected in Thailand. In phylogenetic trees based on 16S rRNA gene sequences and 16S-23S rDNA internal transcribed spacer (ITS) region sequences, the four isolates were located in the lineage of the genus Gluconobacter and constituted a separate cluster from the known Gluconobacter species, Gluconobacter oxydans, Gluconobacter cerinus, and Gluconobacter frateurii. In addition, the isolates were distinguished from the known species by restriction analysis of 16S-23S rDNA ITS region PCR products using three restriction endonucleases Bsp1286I, MboII, and AvaII. The DNA base composition of the isolates ranged from 55.3-56.3 mol% G+C. The four isolates constituted a taxon separate from G. oxydans, G. cerinus, and G. frateurii on the basis of DNA-DNA similarities. Morphologically, physiologically, and biochemically, the four isolates were very similar to the type strains of G. oxydans, G. cerinus, and G. frateurii; however, the isolates were discriminated in their growth at 37 degrees C from the type strains of G. cerinus and G. frateurii, and in their growth on L-arabitol and meso-ribitol from the type strain of G. oxydans. The isolates showed no acid production from myo-inositol or melibiose, which differed from the type strains of the three known species. The major ubiquinone homologue was Q-10. On the basis of the results obtained, Gluconobacter thailandicus sp. nov. was proposed for the four isolates. The type strain is isolate F149-1(T) (=BCC 14116(T)=NBRC 100600(T)=JCM 12310(T)=TISTR 1533(T)=PCU 225(T)), which had 55.8 mol% G+C, isolated from a flower of the Indian cork tree (Millingtonia hortensis) collected in Bangkok, Thailand.