Separation of DNA fragments in DGGE and TGGE is based on the decreased electrophoretic mobility of partially melted double-stranded DNA molecules in polyacrylamide gels containing a linear gradient of DNA denaturants (a mix- ture of urea and formamide) or a linear temperature gradient, which is created by two water baths attached to a c o o l i n g p l a t e u n d e r t h e g e l . ~Iolecules w i t h d i f f e r e n t sequences may have a different melting behavior, and will, therefore, stop migrating at different positions in the gel (for a more detailed description see Muyzer and Smalla [6°°]).
Since the first publication by Muyzer elof [7J in 1993 an incrcasing number of studies in microbial ecology have used DGGE/TGGE. In this review I describe the recent developments of these techniques and discuss why they are so important for ecological studies.