Schematic of bacterial 16S rDNA showing conserved and hypervariable regions. Detailed information about the primers and their superposition on the bacterial 16S rDNA can be found at http://rrna.uia.ac.be/primers/data/BS/sec_model_fw.html. Bact27F (5' AGA GTT TGA TCM TGG CTC AG 3') corresponds to positions 9–27 of the E. coli 16S rDNA and is similar to BSF8/20. Bact517 (5' ATT ACC GCG GCT GCT GG 3') corresponds to positions 517–534 of the E. coli 16S rDNA and is similar to BSF517/17. Bact1492R (5' TAC GGY TAC CTT GTT ACG ACT T 3') corresponds to positions 1492–1514 of the E. coli 16S rDNA. The approximate sites for hypervariable regions (V1-V3) are shown as shaded boxes.