High intragenomic heterogeneity of 16S rRNA genes in a subset of Vibrio vulnificus strains from the western Mediterranean coast.

Heterogeneity among ribosomal operons in Vibrio vulnificus is purported as a probabilistic indicator of strain virulence and classifies V. vulnificus strains as 16S rRNA genes type A and B. In this study, 16S rRNA genes typing of V. vulnificus strains isolated from the Valencia city coast, in the western Mediterranean, showed that 24 out of 30 isolates were type A, one was type B and five could not be typed. Single strand conformation polymorphism (SSCP) analysis of this gene region revealed complex patterns indicative of intragenomic ribosomal operon sequence heterogeneity. The 16S rRNA genes of three untypeable isolates C27, C30, and C34, along with type A (ATCC 27562) and B (C7184) reference strains, were amplified, cloned and sequenced. The number of unique 16S rRNA gene sequences was 4, 3, and 4 for the environmental isolates. The type strain of the species (ATCC 27562) presented only two 16S rRNA gene types, while the reference isolate C7184 of clinical origin had only one 16S rRNA gene type. Sequences differed from five to 35 bp (99.6% to 97.6% sequence similarity). Areas of variability concentrated in helices 10, 18, and 37 and included variants with short intervening sequences in helix 10. Most of the substitutions showed compensatory mutations suggesting ancient sequence divergence generated by lateral gene transfer.