Phylogenetic analysis and identification of Aeromonas species based on sequencing of the cpn60 universal target

An analysis of the universal target (UT) sequence from the cpn60 gene was performed in order to evaluate its usefulness in phylogenetic and taxonomic studies and as an identification marker for the genus Aeromonas. Sequences of 555 bp, corresponding to the UT region, were obtained from a collection of 35 strains representing all of the species and subspecies of Aeromonas. From the analysis of these sequences, a range of divergence of 0-23.3 % was obtained, with a mean of 11.2 +/- 0.9 %. Comparative analyses between cpn60 and gyrB, rpoD and 16S rRNA gene sequences were carried out from the same Aeromonas strain collection. Sequences of the cpn60 UT region showed similar discriminatory power to gyrB and rpoD sequences. The phylogenetic relationships inferred from cpn60 sequence distances indicated an excellent correlation with the present affiliation of Aeromonas species with the exception of Aeromonas hydrophila subsp. dhakensis, which appeared in a separate phylogenetic line, and Aeromonas sharmana, which exhibited a very loose phylogenetic relationship to the genus Aeromonas. Sequencing of cpn60 from 33 additional Aeromonas strains also allowed us to establish intra- and interspecific threshold values. Intraspecific divergence rates were <= 3.5 %, while interspecific divergence rates fell between 3.7 and 16.9 %, excluding A. sharmana. In this study, cpn60 UT sequencing was shown to be a universal, useful, simple and rapid method for the identification and phylogenetic affiliation of Aeromonas strains.