diversity, in mammals. This approach has demonstrated the pervasive influence of the microbiota over a variety of events in the maturation of the gastrointestinal tract, but it raises further questions regarding the potential for individual developmental variation arising from differences in microbiota from one member of a species to another. In humans, such variation could accrue among contemporaries who live in different environments or have different diets, as well as over the course of history.

Once established, the gut microbiota acts as an exquisitely tuned metabolic “organ” within the host, according to presenter Jeffrey Gordon, senior author of the second paper in this chapter. He and coworkers review current knowledge of the structure and function of the human gut microbiota, as well as recent research that reveals coevolution between humans and gut microbes to their mutual benefit. Over the course of evolution, symbiotic gut bacteria have become, in Gordon’s words, “master physiological chemists,” employing a broad range of strategies to manipulate host genomes.

Details of these microbial strategies are revealed in the final contribution to this chapter, in which presenter Abigail Salyers surveys the microbial activities in the human colon that are influenced by diet and that in turn affect human health. These include genetic exchanges among microbes that occur through transformation, phage transduction, and conjugation—interactions that are known to contribute to antibiotic resistance and which may also influence the evolution and virulence of pathogens. Salyers notes that several basic and longstanding questions regarding the composition, function, and evolution of the human intestinal microflora can now be investigated with the advent of molecular technology.

THE ROLE OF THE INDIGENOUS MICROBIOTA IN ZEBRAFISH GASTROINTESTINAL TRACT DEVELOPMENT

Karen Guillemin, Ph.D.

University of Oregon


Although the anatomy of the human gastrointestinal (GI) tract has been explored since at least the time of Leonardo da Vinci, who secretly produced detailed drawings of human organs at a time when such studies were considered heretical, our understanding of this organ is still largely incomplete. That is because we know so little about its cellular composition, which is dominated by microbes. The bacterial community of the GI tract contains an enormous wealth of unsequenced genomic information, and it raises important questions as to its function in the normal physiology and development of this organ.

My coworkers and I are interested in the role commensal bacteria play in animal development, a phenomenon that has gone largely unexplored by developmental biologists. We are using a model vertebrate, the zebrafish, to study GI tract development in the presence and absence of the microbiota. Here I will



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