Phylogeny of the family Moraxellaceae by 16S rDNA sequence analysis, with special emphasis on differentiation of Moraxella species

Thirty-three strains previously classified into 11 species in the bacterial family Moraxellaceae were subjected to phylogenetic analysis based on 16S rRNA sequences, The family Moraxellaceae formed a distinct clade consisting of four phylogenetic groups as judged from branch lengths, bootstrap values and signature nucleotides. Group I contained the classical moraxellae and strains of the coccal moraxellae, previously known as Branhamella, with 16S rRNA similarity of greater than or equal to 95 %. A further division of group I into five tentative clusters is discussed. Group II consisted of two strains representing Moraxella atlantae and Moraxella osloensis. These strains were only distantly related to each other (93.4 %) and also to the other members of the Moraxellaceae (less than or equal to 93 %), Therefore, reasons for reclassification of these species into separate and new genera are discussed. Group III harboured strains of the genus Psychrobacter and strain 752/52 of [Moraxella] phenylpyruvica. This strain of [M.] phenylpyruvica formed an early branch from the group III line of descent, Interestingly, a distant relationship was found between Psychrobacter phenylpyruvicus strain ATCC 23333(T) (formerly classified as [M.] phenylpyruvica) and [M.] phenylpyruvica strain 752/52, exhibiting less than 96% nucleotide similarity between their 165 rRNA sequences, The establishment of a new genus for [M.] phenylpyruvica strain 752/52 is therefore suggested. Group IV contained only two strains of the genus Acinetobacter, Strategies for the development of diagnostic probes and distinctive sequences for 165 rRNA-based species-specific assays within group I are suggested. Although these findings add to the classificatory placements within the Moraxellaceae, analysis of a more comprehensive selection of strains is still needed to obtain a complete classification system within this family.