It should be noted that in two previous DGGE gels where just samples from the phases II and III were loaded, we observed other bands that did not appear in the gel shown in Fig 3. All of these extra bands retrieved in preliminary DGGE analysis represented the GAO population and appeared in the down part of the DGGE gel, meaning that these bacteria had a lower GC content than the others. Therefore, it is possible that the bands representing the GAO population have run out of the gel depicted in Fig. 3. However, even though they were not retrieved in the DGGE gel displayed in Fig. 3, the bands retrieved in previous DGGE analyses representing the GAO population were taken into account in the phylogenetic analysis.