Denaturing gradient gel electrophoresis (DGGE) is a gel electrophoresis method used to separate DNA fragments of the same length, but containing different base — pair sequences; it is used to determine the presence and abundance of different microbial species in a mixed population [12]. It is based on the principle that increasing the denaturant concentration will melt double-stranded DNA in distinct domains. When the melting temperature (Tm) of the lowest domain is reached, the DNA will partially melt, creating branched molecules with reduced mobility in a polyacrylamide gel [13]. DGGE analysis is able to compare many samples at the same time and to analyze them more easily than clone analysis and is thus suitable to reveal microbial community succession.