Ask the Expert: Biome 101

Ask the Expert: Biome 101

March 2022

We are pleased to continue our new series here on The Biome Blog called Ask the Expert with Chief Science Officer Elizabeth DuPriest, Ph.D. 

Q: What exactly is a biome?

A: “Biome” as we are using it here is short for “microbiome”. Whether on a planet-wide scale (a true ecological “biome” such as tundra or rainforest), or as a microenvironment within the body (“microbiome”), a biome is the whole of all the living organisms within a particular location and the environment they interact with.

In our case, we are discussing the vagina (the environment) and the microbial organisms – like bacteria, yeasts, viruses, and even protozoa – that live there. Whether on a large scale or microscopic, living organisms are able to modify their environment to ensure their own success. In the case of the vaginal microbiome, the “environment” also happens to be its own living organism, which may benefit or be harmed by the presence of microbes.

Over 500 microorganisms have been identified in human vaginas[1], though any individual vagina hosts only a small number of species. Healthy vaginal microbiomes consist primarily of Lactobacillus species, especially L. crispatus; and in these healthy biomes, the dominant species may represent 90% or more of the microbial abundance in the vagina[2].

Lactobacillus bacteria interact with the vaginal environment in which they live.

  • First, the food they eat is glycogen, a polysaccharide consisting of repeating glucose units. Glycogen is produced by the cells of the vaginal epithelium (lining) in response to the presence of estrogen and is released through bacterial action as the cells naturally exfoliate. As the lactobacilli metabolize glycogen to obtain energy and carbon, they produce lactic acid, which acidifies the vaginal environment, contributing to the health of the biome.
  • Second, the vaginal surface epithelial cells serve as binding sites for the bacteria, giving them a place to attach.

Unhealthy microbiomes are those which consist of relatively few lactobacilli, and typically have many other species of bacteria present[2]. Yeast, protozoa, and viruses may also be found in an unhealthy biome. The presence of large numbers of these organisms modifies the vaginal tissues, sometimes increasing pH (de-acidifying it), sometimes increasing rate of loss of epithelial layers, and nearly always eliciting an unhealthy response by the host immune system.

These responses can result in inflammatory symptoms like swelling, redness, pain, itchiness, and cause changes in tissue structure and function that increase risk of infections like HIV[3], HPV, HSV, trichomonas, Staphylococcus, Streptococcus, and many others.

Clearly, supporting a healthy microbiome is critical to maintaining health of the vagina and the whole body.


Diop K, Dufour J-C, Levasseur A, Fenollar F. Exhaustive repertoire of human vaginal microbiota. Human Microbiome Journal. 2019;11:100051.

Ravel J, Gajer P, Abdo Z, Schneider GM, Koenig SSK, McCulle SL, et al. Vaginal microbiome of reproductive-age women. Proceedings of the National Academy of Science. 2011;108(Suppl1):4680-4687.

Gosmann C, Anahtar MN, Handley SA, Farcasanu M. Abu-Ali G, Bowman BA, et al. Lactobacillus-deficient cervicovaginal bacterial communities are associated with increased HIV acquisition in young South African women. Immunity. 2017;46(1):29-37.

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