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

Abstract

An analysis of the universal target (UT) sequence from the <i>cpn60</i> gene was performed in order to evaluate its usefulness in phylogenetic and taxonomic studies and as an identification marker for the genus <i>Aeromonas</i>. 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 <i>Aeromonas</i>. 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 <i>cpn60</i> and <i>gyrB</i>, <i>rpoD</i> and 16S rRNA gene sequences were carried out from the same <i>Aeromonas</i> strain collection. Sequences of the <i>cpn60</i> UT region showed similar discriminatory power to <i>gyrB</i> and <i>rpoD</i> sequences. The phylogenetic relationships inferred from <i>cpn60</i> sequence distances indicated an excellent correlation with the present affiliation of <i>Aeromonas</i> species with the exception of <i>Aeromonas hydrophila</i> subsp. <i>dhakensis</i>, which appeared in a separate phylogenetic line, and <i>Aeromonas sharmana</i>, which exhibited a very loose phylogenetic relationship to the genus <i>Aeromonas</i>. Sequencing of <i>cpn60</i> from 33 additional <i>Aeromonas</i> 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 <i>A. sharmana</i>. In this study, <i>cpn60</i> UT sequencing was shown to be a universal, useful, simple and rapid method for the identification and phylogenetic affiliation of <i>Aeromonas</i> strains.