The diversity of the predominant bacteria in the human gastrointestinal tract was studied by using 16S
rRNA-based approaches. PCR amplicons of the V6 to V8 regions of fecal 16S rRNA and ribosomal DNA
(rDNA) were analyzed by temperature gradient gel electrophoresis (TGGE). TGGE of fecal 16S rDNA amplicons
from 16 individuals showed different profiles, with some bands in common. Fecal samples from two
individuals were monitored over time and showed remarkably stable profiles over a period of at least 6 months.
TGGE profiles derived from 16S rRNA and rDNA amplicons showed similar banding patterns. However, the
intensities of bands with similar mobilities differed in some cases, indicating a different contribution to the
total active fraction of the prominent fecal bacteria. Most 16S rRNA amplicons in the TGGE pattern of one
subject were identified by cloning and sequence analysis. Forty-five of the 78 clones matched 15 bands, and 33
clones did not match any visible band in the TGGE pattern. Nested PCR of amplified 16S rDNA indicated
preferential amplification of a sequence corresponding to 12 of the 33 nonmatching clones with similar
mobilities in TGGE. The sequences matching 15 bands in the TGGE pattern showed 91.5 to 98.7% homology
to sequences derived from different Clostridium clusters. Most of these were related to strains derived from the
human intestine. The results indicate that the combination of cloning and TGGE analysis of 16S rDNA
amplicons is a reliable approach to monitoring different microbial communities in feces.