Biodiversity of vibrios

Abstract

Vibrios are ubiquitous and abundant in the aquatic environment. A high abundance of vibrios is also detected in tissues and/or organs of various marine algae and animals, e.g., abalones, bivalves, corals, fish, shrimp, sponges, squid, and zooplankton. Vibrios harbour a wealth of diverse genomes as revealed by different genomic techniques including amplified fragment length polymorphism, multilocus sequence typing, repetetive extragenic palindrome PCR, ribotyping, and whole-genome sequencing. The 74 species of this group are distributed among four different families, i.e., Enterovibrionaceae, Photobacteriaceae, Salinivibrionaceae, and Vibrionaceae. Two new genera, i.e., Enterovibrio norvegicus and Grimontia hollisae, and 20 novel species, i.e., Enterovibrio coralii, Photobacterium eurosenbergii, V. brasiliensis, V. chagasii, V. coralliillyticus, V. crassostreae, V. fortis, V. gallicus, V. hepatarius, V. hispanicus, V. kanaloaei, V. neonatus, V. neptunius, V. pomeroyi, V. pacinii, V. rotiferianus, V. superstes, V. tasmaniensis, V. ezurae, and V. xuii, have been described in the last few years. Comparative genome analyses have already revealed a variety of genomic events, including mutations, chromosomal rearrangements, loss of genes by decay or deletion, and gene acquisitions through duplication or horizontal transfer (e.g., in the acquisition of bacteriophages, pathogenicity islands, and super-integrons), that are probably important driving forces in the evolution and speciation of vibrios. Whole-genome sequencing and comparative genomics through the application of, e.g., microarrays will facilitate the investigation of the gene repertoire at the species level. Based on such new genomic information, the taxonomy and the species concept for vibrios will be reviewed in the next years.

FIG. 1.

Phylogenetic tree based on the neighbor-joining method, using the 16S rRNA, recA and rpoA concatenated gene sequences (2,898 bp), showing the different families of vibrios. Distance estimations were obtained by the model of Jukes and Cantor (196). Bootstrap percentages after 1,000 simulations are shown. Bar, 1% estimated sequence divergence. Sequences originated from the type strains of each species. The rpoA and recA gene sequences are from our own databases.

FIG. 2.

Polynomial regression (second degree) of FAFLP versus DNA-DNA homology data. FAFLP pattern pairwise similarities were calculated with the Dice coefficient, and 0.2% band position tolerance was used to allow technical errors. The diagonal (i.e., 100% theoretical values) of the DNA-DNA hybridization matrices was not included, in order to give a more realistic view of the relationship between the two techniques. The dashed line indicates the threshold (70% DNA-DNA similarity) for species-level circumscription.