tem (Bio-Rad Laboratories Inc.). PCR products from
three denitrifying strains were applied two times to each
DGGE gel as markers to check the electrophoresis run
and to compare fragment migration between gels. For
nirS the strains were (in the order of increasing migration
distance): Pseudomonas fluorescens Mi32, Paracoccus
denitrificans CCUG 13798 and P. denitrificans Pd1222;
for nirK: Alcaligenes faecalis ATCC 8750, Achromobacter cycloclastes ATCC 21921 and Alcaligenes sp. DSM
30128; and for nosZ: Ralstonia eutropha CCUG 13724,
B. denitrificans DSM 1113 and P. denitrificans Pd 1222.
One-mm thick, 16 by 16 cm polyacrylamide gels
(7.0% [v/v] acrylamide-bisacrylamide [37.5:1]; denaturant [urea and formamide]) were poured using a gradient
maker (Bio-Rad Laboratories Inc.). A mixture of 7 M