Vibrios commonly possess two chromosomes

Abstract

The prevalence of the two-chromosome configuration was investigated in 34 species of vibrios and closely related species. Pulsed-field gel electrophoresis of undigested genomic DNA suggested that vibrios commonly have two chromosomes. The size of the large chromosome is predominantly within a narrow range (3.0 to 3.3 Mb), whereas the size of the small chromosome varies considerably among the vibrios (0.8 to 2.4 Mb). This fact suggests that the structure of the small chromosome is more flexible than that of the large chromosome during the evolution of vibrios.

FIG. 1.

PFGE of intact genomic DNAs of bacterial species belonging to the genus Vibrio. Lanes: 1 and 2, Schizosaccharomyces pombe and Hansenula wingei PFGE markers, respectively; 3, V. hollisae; 4, V. metschnikovii; 5, V. cholerae (El Tor); 6, V. anguillarum; 7, V. furnissii; 8, V. orientalis; 9, V. parahaemolyticus (RIMD2210633); 10, V. splendidus; 11, V. vulnificus; 12, V. alginolyticus; 13, V. harveyi; 14, V. nigripulchritudo; 15, H. wingei PFGE marker.

FIG. 2.

Phylogenetic tree based on 16S rRNA genes showing the relationships of the strains listed in Table 1. Strains possessing one chromosome are indicated in red, and strains possessing two chromosomes are shown in blue. This tree is based on a 1,152-bp alignment of 16S rRNA gene sequences and was constructed by using the neighbor-joining method. Accession numbers for the sequences are given in parentheses. To estimate the root position of the tree, Halomonas elongata ATCC 33173^T (accession no. X67023) and Pseudomonas aeruginosa PAO1 (accession no. NC002516) were used as an outgroup. Numbers at the nodes indicate the levels of bootstrap support (percentages) based on a neighbor-joining analysis of 1,000 resampled data sets; only values above 50% are shown. Asterisks indicate branches that were also recovered by using the maximum-parsimony and maximum-likelihood methods. Bar, 0.01 substitution per nucleotide position.