When we want to extract a DNA sequence from a mixture of sequences coming from a core sediment sample, for example, we must use techniques in order to succeed in pinning down this sequence. DGGE is one of these techniques. It is a method of separation and isolation of DNA sequences based on their denaturation characteristics (see Polymerase Chain Reaction).

Each DNA is different. What differentiates them is the chain of nucleotides. The As are linked to Ts, and the Gs are linked to Cs. The AT links are less solid than GC links and these denature more easily. 

In the case of DGGE, the denaturation is not done by means of an increase in temperature but with the help of a chemical denaturant placed in an electrically charged gel. The nearer to the positive pole of the gel the more the solution is concentrated in chemical denaturant. When placed on the gel, the negatively charged DNA migrates towards the positive pole. The DNA having more AT connections denatures more quickly and become immobilised in the gel. Conversely, the DNA composed of more GC connections migrates further in the gel where the denaturant is more concentrated. 

The different DNA chains will therefore be isolated. It only remains to extract the required DGGE bandand apply the PCR to amplify and analyse its sequence, and finally to know to which species the sequence belongs, thanks to the ribosomal 16S rRNA sequence.

DGGE is only one method among many others. DNA sequencing has been constantly evolving over the last thirty years or so. Effective high-throughput sequencing techniques are being born and are becoming widely accessible.