Thirty six predominant colonies were iso-lated from the SBR and control reactor sam-ples and reduced to 14 restriction fragment
length polymorphism (RFLP) profiles by
RFLP analysis. Although the colonies isolated
in each bioreactor sample showed different
RFLPs, some appeared in more than one (Ta-ble 2). The most frequent bacteria isolated
from all bioreactors were members belonging
to Paracoccus and Pseudomonas. The most
widely represented phylum (11 members) was
that of the Proteobacteria, with bacteria from
the Alfa proteobacteria (Paracoccus),
Gamma-Proteobacteria (Pseudomonas and
Aeromonas) and Beta-Proteobacteria (Coma-monas) classes. The remaining bacteria are
distributed in equal proportions among the
Bacteroides (Flavobacterium) and Actinobac-teria phyla. PCR amplification experiments
showed that all isolated denitrifying bacteria
harbour the nosZ gene, responsible for the last
step in the denitrification pathway (reduction
of nitrous oxide to molecular nitrogen (data
not shown).