Phylogenetic Analysis of Acinetobacter Strains Based on the Nucleotide Sequences of GyrB Genes and on the Amino Acid Sequences of Their Products

Partial nucleotide sequences of the gyrB genes (DNA gyrase B subunit genes) of 15 Acinetobacter strains, including the type and reference strains of genomic species 1 to 12 (A. calcoaceticus [genomic species 1], A. baumannii [genomic species 2], Acinetobacter genomic species 3, A. haemolyticus [genomic species 4], A. junii [genomic species 5], Acinetobacter genomic species 6, A. johnsonii [genomic species 7], A. lwoffii [genomic species 8], Acinetobacter genomic species 9, Acinetobacter genomic species 10, Acinetobacter genomic species 11, and A. radioresistens [genomic species 12]), were determined by sequencing the PCR-amplified fragments of gyrB. The gyrB sequence homology among these Acinetobacter strains ranged from 69.6 to 99.7%. A phylogenetic analysis, using the gyrB sequences, indicates that genomic species 1, 2, and 3 formed one cluster (87.3 to 90.3% identity), while genomic species 8 and 9 formed another cluster (99.7% identity). These results are consistent with those of DNA-DNA hybridization and of biochemical systematics. On the other hand, the topology of the published phylogenetic tree based on the 16S rRNA sequences of the Acinetobacter strains was quite different from that of the gyrB-based tree. The numbers of substitution in the 16S rRNA gene sequences were not high enough to construct a reliable phylogenetic tree. The gyrB-based analysis indicates that the genus Acinetobacter is highly diverse and that a reclassification of this genus would be required.