A metagenomic analysis of the dynamic changes of the composition of the
intestinal microbiome of five participants of the MARS-500 experiment was
performed. DNA samples were isolated from the feces of the participants taken
just before the experiment, upon 14, 30, 210, 363 and 510 days of isolation in
the experimental module, and two weeks upon completion of the experiment. The
taxonomic composition of the microbiome was analyzed by pyrosequencing of 16S
rRNA gene fragments. Both the taxonomic and functional gene content of the
microbiome of one participant were analyzed by whole metagenome sequencing
using the SOLiD technique. Each participant had a specific microbiome that
could be assigned to one of three recognized enterotypes. Two participants had
enterotype I microbiomes characterized by the prevalence of
Bacteroides, while the microbiomes of two others, assigned to
type II, were dominated by Prevotella. One participant had a
microbiome of mixed type. It was found that (1) changes in the taxonimic
composition of the microbiomes occurred in the course of the experiment, but
the enterotypes remained the same; (2) significant changes in the compositions
of the microbiomes occurred just 14-30 days after the beginning of the
experiment, presumably indicating the influence of stress factors in the first
stage of the experiment; (3) a tendency toward a reversion of the microbiomes
to their initial composition was observed two weeks after the end of the
experiment, but complete recovery was not achieved. The metagenomic analysis of
the microbiome of one of the participants showed that in spite of variations in
the taxonomic compositions of microbiomes, the “functional” genetic composition
was much more stable for most of the functional gene categories. Probably in
the course of the experiment the taxonomic composition of the gut microbiome
was adaptively changed to reflect the individual response to the experimental
conditions. A new, balanced taxonomic composition of the microbiome was formed
to ensure a stable gene content of the community as a whole without negative
consequences for the health of the participants.
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