Small samples of DNA (or RNA) are added to an electrophoresis gel that contains a denaturing agent. The denaturing gel induces melting of the DNA at various stages. As a result of this melting, the DNA spreads through the gel and can be analyzed for single components.
DGGE (Muyzer et al. 1993) analyses are employed for the separation of double-stranded DNA fragments that are identical in length, but differ in sequence.
In practice, the DNA fragments are usually produced via PCR amplification. The DGGE technique exploits (among other factors) the difference in the stability of G-C pairing (3 hydrogen bonds per pairing) as opposed to A-T pairing (2 hydrogen bonds). A mixture of DNA fragments of different sequence is separated by electrophoresis on an acrylamide gel containing a linearly increasing gradient of DNA denaturants (usually urea and formamide). In general, DNA fragments richer in GC will be more stable and remain double-stranded until reaching higher denaturant concentrations. Double-stranded DNA fragments migrate better in the acrylamide gel, while denatured DNA molecules slow down or stop in the gel. In this manner, DNA fragments of differing sequence can be separated in an acrylamide gel. DGGE is commonly performed for partial 16S rRNA gene, but also functional genes may be used. A GC (guanine plus cytosine) rich sequence can be incorporated into one of the primers used in the PCR to modify the melting behaviour of the fragment of interest and to improve the separation of the fragments. The DGGE gels can be stained with DNA binding fluorescent dyes, such as SYBR Green and visualized under UV light. Known standards may be used for comparing the samples on different gels. Ideally one band on the gel corresponds to one species, and therefore the number of bands gives an idea of the diversity of the sample. The gene fragments can be excised from the gel, eluted e.g. into sterile water and amplified for sequencing. The relative abundance of various microorganisms can be estimated by measuring the intensity of their bands relative to the intensity of all bands in the corresponding sample.
Small samples of DNA (or RNA) are added to an electrophoresis gel that contains a denaturing agent. The denaturing gel induces melting of the DNA at various stages. As a result of this melting, the DNA spreads through the gel and can be analyzed for single components.DGGE (Muyzer et al. 1993) analyses are employed for the separation of double-stranded DNA fragments that are identical in length, but differ in sequence.In practice, the DNA fragments are usually produced via PCR amplification. The DGGE technique exploits (among other factors) the difference in the stability of G-C pairing (3 hydrogen bonds per pairing) as opposed to A-T pairing (2 hydrogen bonds). A mixture of DNA fragments of different sequence is separated by electrophoresis on an acrylamide gel containing a linearly increasing gradient of DNA denaturants (usually urea and formamide). In general, DNA fragments richer in GC will be more stable and remain double-stranded until reaching higher denaturant concentrations. Double-stranded DNA fragments migrate better in the acrylamide gel, while denatured DNA molecules slow down or stop in the gel. In this manner, DNA fragments of differing sequence can be separated in an acrylamide gel. DGGE is commonly performed for partial 16S rRNA gene, but also functional genes may be used. A GC (guanine plus cytosine) rich sequence can be incorporated into one of the primers used in the PCR to modify the melting behaviour of the fragment of interest and to improve the separation of the fragments. The DGGE gels can be stained with DNA binding fluorescent dyes, such as SYBR Green and visualized under UV light. Known standards may be used for comparing the samples on different gels. Ideally one band on the gel corresponds to one species, and therefore the number of bands gives an idea of the diversity of the sample. The gene fragments can be excised from the gel, eluted e.g. into sterile water and amplified for sequencing. The relative abundance of various microorganisms can be estimated by measuring the intensity of their bands relative to the intensity of all bands in the corresponding sample.
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