primers, R3cd, R3Cu and nosZ1622R. The introduction
of the GC-clamp did not affect the amplification efficiency of either the denitrifying strains or the environmental samples. After amplification, the three different
DGGE methods in our study were optimised regarding
gradient concentration and running time using amplicons from the denitrifying strains as controls. We initially experienced problems with multiple bands, but
once the DGGE methods were optimised, only one band
appeared on the gel from each of the pure cultures
without any smear. After the DGGE optimisations,
partial nirK and nosZ genes from denitrifying pure cultures were clearly separated from each other and covered the whole gradient, but the nirS-gene separation
was not as good (e.g., Fig. 2).