One of the major challenges in microbial ecology for the future is to establish links between structural and functional biodiversity. This is particularly difficult when one is interested in a phylogenetically diversified function such as denitrification. The data banks are very rich in functional gene sequences (nirS in this study), but most of them were obtained from not yet cultivated bacteria, and thus must be supplemented by sequences of organisms from the environment for which we could associate a taxonomic position and physiological characteristics. Combined analysis including molecular (16S-rRNA or nirS genes), physiological, and biochemical approaches was carried out on a bacterial set of 89 strains isolated from marine sediment. The denaturing gradient gel electrophoresis (DGGE) technique was successfully applied on unclamped polymerase chain reaction (PCR) products of nirS genes to compare the picture of the biodiversity obtained with 16S rRNA and nirS genes. The diversity of nirS genes and denitrifier characteristics were found within several of the 16S rDNA phylotypes. In contrast, the nirS phylotypes were no diverse both with respect to 16S rDNA and to physiology and biochemistry of denitrification. Sequences of the nirS PCR products were very close to marine environmental clones and were analyzed within the same phylogenetic tree.