Micro-Editorial: MICROBIOTA

One Health Newsletter: Volume 10 Issue 2

October 2018

Every surface of all multicellular organisms, including animal and plants, exposed to the environment, are colonized by a diverse microbial community of bacteria, archaea, protists, fungi and viruses that constitute an ecological community of microbes called the microbiota.

All microbiota members largely outnumber host eukaryotic cells, acting for their host as commensal (e.g., Mammalian gut and Escherichia coli, Aspergillus spp., Staphylococcus), symbiotic (e.g., Mammalian gastrointestinal tract and Lactobacillus, Bacteroides fragilis), probiotic microorganisms (e.g., Human central nervous system vs. Bifidobacterium spp. and Lactobacillus spp.) and/or pathogenic (e.g., Helicobacter pylori vs. stomach microbiota) microorganisms. Moreover, members of this microbial community interact with each other, potentially having direct consequences on their host. Such types of inter-microbial dynamics can eventually occur as: synergistic (e.g., intestinal microbiota supporting healthy digestive and immune function), antagonistic (e.g., immune cross protection of two close related microorganisms), or independent or having interaction not yet demonstrated. In order to survive the microbiota, microorganisms are in equilibrium (pathocenosis) or not competing, mostly because they are in different host biological compartment (e.g., blood parasites and ecto-parasites: plasmodium and skin fungus).

As much as Microbiota has been studied in several hosts for more than a century, such ecological communities of microbes have been found to be critical for immunologic, hormonal and metabolic homeostasis of their host including, among others, mammals (e.g., human, herbivores), but also amphibians, insects and plants.

Collectively, the viruses constitute the virome and microbes (bacteria and fungus) constitute the microbiome. In addition, the microbiome generally describes either the collective microorganism genomes or, the microorganisms themselves that reside in an environmental niche. Altogether, virome, microbiome and host, refer to holobiont, with a collective genomic nucleotide called, hologenome.

The hologenome theory, a phenomenon of co-evolution, considers that microbiota and host (i.e., hologenome) emerged during evolution as a synergistic unit of concurrent long-term microorganisms and eukaryotic co-existence, as well as relentless interactions between microbiota members with direct effects on their host. Among others, the co-evolution of coral reef microbiota has been instrumental to develop the theory concept. Ultimately, this theory considers that natural selection of individual organisms is the totality of all organisms associated in the same eco-system, including its microbial communities.

The following examples of host and microbial community interaction presented in this OHNL issue give some insight into such mechanisms of interaction. Indeed, we will see that members of the microbiota compete with pathogens for colonization sites and surviving resources, and therefore, can potentially alter host’s homeostasis.

Next story: Antimicrobial Compounds and the Gastrointestinal Microbiome: Implications for Health and Disease

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