Summary auto-generated
This study evaluated the recA gene as an alternative phylogenetic marker for identifying and classifying bacteria in the family Vibrionaceae, particularly the genus Vibrio. Researchers sequenced a 739 bp fragment of the recA gene from 62 Vibrionaceae strains and compared the results with 16S rDNA sequences. The analysis revealed that the genus Vibrio is polyphyletic, with significant heterogeneity among species. RecA sequences proved much more discriminatory than 16S rDNA for distinguishing closely related species. For example, strains with >98% 16S rDNA similarity showed recA similarities ranging from 83-99%. The study found that strains of the same species shared at least 94% recA sequence similarity. Photobacterium species nested within vibrios despite only 84% recA similarity, while Grimontia hollisae was distantly related. Specific species groups, such as Vibrio cholerae and Vibrio mimicus, clustered separately, and the V. splendidus-related group appeared highly homogeneous. The moderate correlation (0.58) between recA and 16S rDNA data, combined with recA's superior discriminatory power, suggests it represents a valuable complementary tool for rapid and reliable identification of Vibrionaceae species alongside existing methods.
Key findings
- RecA gene sequences are significantly more discriminatory than 16S rDNA for distinguishing closely related Vibrio species, with 16S similarity >98% corresponding to recA similarities ranging from 83-99%
- The genus Vibrio is polyphyletic, with distinct clustering of V. cholerae/V. mimicus, V. harveyi-related species, and V. splendidus-related species forming separate groups
- Strains of the same Vibrio species share at least 94% recA sequence similarity, suggesting this threshold can be used for species identification
- Photobacterium species are apparently nested within vibrios despite lower recA similarity (maximum 84% to Vibrio), indicating complex phylogenetic relationships within Vibrionaceae
- RecA sequences show no evidence of horizontal gene transfer or recombination and correlate well with previous polyphasic taxonomic studies and AFLP analysis
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Abstract
This study analysed the usefulness of recA gene sequences as an alternative phylogenetic and/or identification marker for vibrios. The recA sequences suggest that the genus Vibrio is polyphyletic. The high heterogeneity observed within vibrios was congruent with former polyphasic taxonomic studies on this group. Photobacterium species clustered together and apparently nested within vibrios, while Grimontia hollisae was apart from other vibrios. Within the vibrios, Vibrio cholerae and Vibrio mimicus clustered apart from the other genus members. Vibrio harveyi- and Vibrio splendidus-related species formed compact separated groups. On the other hand, species related to Vibrio tubiashii appeared scattered in the phylogenetic tree. The pairs Vibrio coralliilyticus and Vibrio neptunius, Vibrio nereis and Vibrio xuii and V. tubiashii and Vibrio brasiliensis clustered completely apart from each other. There was a correlation of 0·58 between recA and 16S rDNA pairwise similarities. Strains of the same species have at least 94 % recA sequence similarity. recA gene sequences are much more discriminatory than 16S rDNA. For 16S rDNA similarity values above 98 % there was a wide range of recA similarities, from 83 to 99 %.