Evolving as a holobiont

During this past decade, scientists have come to realize the importance of all the bacteria, fungi, and other single-celled microorganisms living in our gastrointestinal (GI) tract. As mentioned before on these GEITP pages, total DNA content of a human includes 8% of his/her own DNA and 92% derived from the enormous numbers of bacteria..!! Termed “the holobiont,” the microbiome (DNA of all symbiotic bacteria living inside each host and its organs) forms a close functional entity (symbiosis) having evolutionarily-designed interactions that support nutritional intake, defense mechanisms, and reproduction. And it’s not just humans or mammals, but insects and other invertebrates (i.e. anything having a “gut” or tube that food passes through).

This evolutionary symbiosis is reminiscent of DNA sequencing studies over the past 3 decades, showing that animal-plant symbiosis has been occurring for hundreds of thousands of years, e.g. ant or some insect feeding on a particular plant leaf, etc.

From the way we eat, to the way we think, to our susceptibility to diseases (just to name a few examples), the microbiome has a huge impact on human physiology. The composition and function of microbiomes are critical for most animals and plants, so much so that many scientists believe hosts and their microbiomes should be considered as single ecological unit –– the holobiont. The attached paper provides an overview of the ubiquity and importance of the holobiont, and how researchers are now investigating this symbiotic relationship between hosts and microbes has evolved over evolutionary time.

A subset of the holobiont (predicted to become much more studied in the near future) has been named the “brain-gut-microbiome.” Implications now are that functions of the central nervous system (CNS) –– including behavior, hunger, CNS diseases, even the mindset to become successful) –– are all influenced by the GI tract and microbiome of these microorganisms living within.

PloS Biol 2o17 15: e2002168 

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