| Scientist - News - 11-12-2007: Stability of the human gut microbiota Rajiliæ-Stojanoviæ, Mirjana The human gut microbiota is a complex ecosystem that inhabits the entire digestive system. The gut microbiota is tremendously important since it performs numerous functions that are essential for the host’s well-being. Despite its importance, the gut microbiota, is nowadays one of the most poorly understood parts of the human body. Some of the remarkable already established findings about the microbiota were described by E.G. Zoetendal, who showed by using a fingerprinting technique, that the microbiota of each person is individual-specific, stable in time and strongly influenced by the host’s genotype. These findings have been confirmed in a number of subsequent studies. However, not everybody in the scientific community agrees on the importance that genotype plays in establishment of a specific gut microbiota. There is a number of scientists that speculated that the individual specific microbiota composition is a mere result of a series of stochastic events that a person experiences. Supporting evidence for this hypothesis was published earlier this year when S. Palmer and co-workers showed, using a phylogenetic microarray approach, that the microbiota of infants develops from a simple community into an adult like microbiota, which has equal similarity to the gut microbiota of their parents and unrelated adults. To shed some more light on this problem and to try to reveal the influence of genotype, environment and stochastic factors on the gut microbiota, a series of experiments that employed another recently developed phylogentic microarray platform (the HITChip), was performed at Wageningen University. M. Rajiliæ-Stojanoviæ and colleagues have assessed the gut microbiota profiles of five individuals over a time span of four years. Despite the four years, during which these individuals lived an active life which included traveling overseas, antibiotic therapies, pregnancies and changing eating habits, the microbiota preserved its unique composition which could be easily distinct from the gut microbiota of other subjects. This remarkable finding shows that the microbiota has a potential to preserve its unique composition regardless the strong environmental triggers. Nevertheless, environmental parameters do play an active role in shaping the intestinal microbiota, which is supported by the fact that the individual gut microbiota is more alike when samples are taken in shorter time intervals. Furthermore, scientists at Wageningen University have shown that not all members of the intestinal microbiota resist the environmental triggering in the same manner. For instance Bifidobacterium spp. and some Bacteroidetes spp. were almost entirely preserved in composition and quantity even during a period of four years. Interestingly, these specific bacteria represent the subpopulations of the gut microbiota that are most alike in monozygotic twin pairs, which suggests that the host’s genotype is most actively influencing these specific groups within the gut microbiota. Active cross-talk between intestinal bacteria and the host, mediated via Toll-like receptors has already been described. There is no evidence available that the host is able to discriminate between specific groups of intestinal bacteria. However, the fact that the Bifidobacterium spp. and some Bacteroidetes spp. are being selectively preserved throughout years, and that these bacterial groups are the pioneering colonizers of the human digestive tract, that promote health of the host by vitamin production or protection against intestinal diseases, are indirectly suggesting that these subpopulations of the gut microbiota might be specifically recognized and conserved by the host. Mechanisms by which the gut microbiota recovers after it has been severely disturbed by environmental factors (e.g. by antibiotics) are still not known. Recently R.R. Bollinger and co-workers proposed that the vermiform appendix serves as a “safe house” of intestinal bacteria. According to their hypothesis, microbes that form a stable biofilm in the appendix are used for the re-inoculation of the intestine after an event in which the commensal microbiota was seriously compromised. If this is the mechanism by which individual-specific and long-term gut microbiota composition is maintained remains to be shown. Nevertheless, many novel findings and novel hypothesis about the human gut microbiota, which have been reported only during the past decade, continue to expand our knowledge about the “forgotten organ” of the human body. Recommended literature [1-13]:
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