Isolation and characterization of small naturally occurring plasmids from Desulfovibrio spp.

Abstract

These results suggest that these strains have different genomic organization. The presence of plasmid DNA was only detected in Desulfovibrio SR-1. On the basis of distinct phenotypic and genotypic characteristics, strain Desulfovibrio SR-1 represents a novel subspecies of D. africanus . Molecular techniques applied to microbial taxonomy were used for the discrimination between Desulfovibrio SR-1 and Desulfovibrio africanus. Desulfovibrio SR-1 has a single polar flagellum and ferments pyruvate. D. africanus has lophotrichus flagella and pyruvate does not support its growth in sulfate-free media. The 16S rRNA gene and the ITS sequence analyses showed the same phylogenetic affiliation for both strains. The DNA sequences of the ITS region of Desulfovibrio SR-1 and D. africanus contain two transfer RNA genes (tRNAIle, tRNAAla), and they are 300 and 299 bases in length, respectively. The analysis of dsrAB sequences showed a better discrimination power than the 16S rRNA sequences in defining their phylogenetic affiliation. The 72% DNA-DNA similarity value did not conclusively resolve whether these strains should be considered as members of one species. The 62.4 mol% G+C content of Desulfovibrio SR-1 differs from the 63.1 mol% G+C of D. africanus. Significant differences in the genomic fingerprints (16S rDNA, PmeI-PFGE and BOX-PCR) between both strains were observed.