Reviews in Basic and Clinical GastroenterologyMicrobes in Gastrointestinal Health and Disease
Section snippets
Evolutionary History of the Gut and Its Associates
Eukaryotes existed in close alliance with microbes even before the appearance of multicellular life.2, 3, 4 Indeed, the very nature of the ancestral eukaryotic animal cell was radically changed by the capture and co-option of endosymbiotic prokaryotes that had the biochemical/metabolic capacity for oxidative phosphorylation, resulting in the formation of the mitochondria, intracellular organelles that are vital and defining features of eukaryotic animal cells.5 Symbiotic relationships, by
Overview of Human Microbiota
The human normal flora, or microbiota, is vast, both in its absolute quantitative mass and its qualitative diversity. A detailed inventory of the normal microbiota was long considered nearly unattainable by conventional microbiologic techniques; however, recent initiatives utilizing high-throughput sequencing and molecular taxonomic methodologies have greatly increased our understanding of the population composition, dynamics, and ecology of the gut microbiota (reviewed in several reports6, 49,
The Hygiene Hypothesis
Although it is important to consider the evolution of prokaryotic-eukaryotic interactions in understanding the mechanisms of gut-microbe interactions, clinical and epidemiologic studies have revealed the importance of this relationship to human health. Although great improvements in human health and longevity stem largely from 19th-century advances in sanitation and public health that reduced mortality from epidemics of infectious disease, recent observations have indicated that not all
Probiotics
There is currently much interest in deliberately manipulating the normal microbiota to accrue health benefits through an approach known as “probiotics.” Probiotics are defined as “live microorganisms which when administered in adequate amounts confer a health benefit on the host.”151 Clearly, the conceptual basis of probiotics is well grounded.121, 137, 152 Therapeutic bacteria could presumably provide the same beneficial functions and activities that have evolved for the normal microbiota. For
Summary
An intricate symbiotic relationship has evolved between humans and microbes. We more fully understand the degree to which gastrointestinal biology is intertwined with microbiology, that the relationship between host and microbe is required for health, and that this relationship might be manipulated therapeutically (Table 2). Perhaps one day, an optimal microbiota will be considered one aspect of nutrition that is as amenable to intervention. Finally, with a fuller understanding of the
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The authors disclose the following: Supported by National Institutes of Health grants DK071604 and AI064462.