PCR products recovered with the CTO primers were subjected to
DGGE according to the protocol of Muyzer et al. [20] as adapted by
Kowalchuk et al. [17] for the study of ammonia-oxidising bacteria.
Gels contained a 38-50% gradient of denaturing chemicals with
100% denaturant defined as 7 M urea and 40% formamide. DNA was
visualized after ethidium bromide staining by UV transillumination,
and gel images were stored using `The Imager’ system. DNA in the
polyacrylamide gels was blotted to Hybond-N. Nucleic Acid Transfer
Membranes (Amersham, UK), using a Transblot SD (Bio-Rad)
according to Muyzer et al