Applied and Environmental Microbiology, November 1999, p. 4799-4807, Vol. 65, No. 11
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Laboratoire d'Ecologie et Physiologie du
Système Digestif,
Received 12 April 1999/Accepted 31 August 1999
The human intestinal tract harbors a complex microbial ecosystem
which plays a key role in nutrition and health. Although this
microbiota has been studied in great detail by culture techniques, microscopic counts on human feces suggest that 60 to 80% of the observable bacteria cannot be cultivated. Using comparative analysis of
cloned 16S rRNA gene (rDNA) sequences, we have investigated the
bacterial diversity (both cultivated and noncultivated bacteria) within
an adult-male fecal sample. The 284 clones obtained from 10-cycle PCR
were classified into 82 molecular species (at least 98% similarity).
Three phylogenetic groups contained 95% of the clones: the
Bacteroides group, the Clostridium coccoides
group, and the Clostridium leptum subgroup. The remaining
clones were distributed among a variety of phylogenetic clusters. Only
24% of the molecular species recovered corresponded to described
organisms (those whose sequences were available in public databases),
and all of these were established members of the dominant human fecal flora (e.g., Bacteroides thetaiotaomicron,
Fusobacterium prausnitzii, and Eubacterium
rectale). However, the majority of generated rDNA sequences
(76%) did not correspond to known organisms and clearly derived from
hitherto unknown species within this human gut microflora.
*
Corresponding author. Mailing address: UEPSD, bat. 405, INRA, Domaine de Vilvert, 78352 Jouy-en-Josas Cedex, France. Phone: 33 (0) 1 34 65 27 09. Fax: 33 (0) 1 34 65 24 92. E-mail:
suau{at}biotec.jouy.inra.fr.
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