DGGE patterns of natural samples are very complex, often because of the abundance of uncultured or—by present techniques—uncultivable bacteria.To simplify DGGE patterns, specific primer sets for 16S rRNA genes or for other functional genes of selected bacterial groups which focus the DGGE on accessible subsets of the natural bacterial population can be designed . DGGE analysis and sequence identification of novel or previously uncultured groups of bacteria give no hints as to the culture conditions and physiology of the respective bacteria.