More on How Little We Know About Archaea

Twice ever, I have gotten to write about archaea, some of the least studied members of the human biome.  These sort-of bacteria (they are kind of like bacteria but their cell walls are different and they have no defined nucleus) are actually pretty remarkable in that they have adapted to live in the most extreme environments, like high heat, high acidity, high salt.  Right now, very little is known about how they affect human health but we are all chock full of ‘em.

In my April 2, 2019 post about archaea, I wrote about a study which looked at their potential role in the development of childhood asthma. Researchers found that a high level of a species called Methanosphaera stadtmanae appears to be protective for not only the development of asthma in children, but also possibly eczema, airborne and food allergies.  I also mention, in that post, another recent paper that discussed the impact of methanogens (which are archaea that produce methane) on health:  “Methanobrevibacter smithii and Methanosphaera stadtmanae are specifically recognized by the human innate immune system, and it is considered that these species contribute to immune responses in the body, including inflammatory responses.”  It is suspected they play a role in the development of inflammatory bowel disease, obesity, irritable bowel syndrome, metabolic diseases, and more.  In other words –  research on this family of organisms is desperately needed.

And thus, I was very glad to spot a new paper this past weekend by researchers at Kiel University in Germany.[i]  They note that as little as is currently known about the methane producing archaea, it’s a lot compared to other kinds, about which we really know nothing.  Here are a few things we do know:  1. Methanogenic archaea are dependent on their bacterial neighbors to provide them substrate (food) – which obviously points to a major co-dependency that has yet to be comprehensively explored; 2. We know that archaea are recognized by the human immune system, and that the levels of pro-inflammatory cytokines released differ for different archaeal species.  3.  Differing levels of Methanobrevibacter smithii and Methanosphaera stadtmanae are associated with different diseases, although the mechanism of action is unknown.

We also apparently know that some archaea seem to break down trimethylamines, those molecules from the consumption of animal products that cause arteriosclerosis.  In fact, clinical trials are actually underway to test the use of these archaea.  On the other hand, increased levels of other archaea seem to be associated with the development of colon cancer and IBD.  These scientists plan on studying the involvement of archaea in human disease in further research.[ii]

A few other highlights of this article:

1. We know that several factors seem to influence the “…presence, abundance and diversity of archaea in the human gut” including geography, ethnicity, genetics, age, life history, gut microbiota composition and diet.
2. Back to bacteria/archaea interactions, just a couple of known examples: M.smithii correlates to certain types of Firmicutes, and Christensenellaceae species positively correlate to a different kind of archaea, Methanobrevibacter. Candida fungi also tend to co-occur with M.smithii.  So much more work needs doing in this!
3. Because the methane producing archaea are so plentiful, they seem to be the best studied. The production of methane gas in the intestines can be measured in breath tests, available since the 1970s, and in studies, has been tested in colon cancer, diverticulosis, diabetes, obesity and anorexia, inflammatory bowel diseases, and many more.  Unfortunately, the data are a mess – full of contradictions, inconsistent techniques for measurement, etc., so are essentially useless:  thus, “…the involvement of archaea in human health and disease often remains blurry.”
4. An interesting finding: “…several sites of the human body are known to present a higher prevalence and abundance of methanogenic archaea.  For example, M.smithii was reported in the vagina only in patients suffering from vaginosis and was absent in healthy individuals.”  And another example: “M.smithii was found in individuals with muscle abscesses, pneumonia and urinary tract infections…”  Weird, right?
5. The prevailing explanation for #4 is that by consuming H2, they promote the growth of fermentative bacteria involved in inflammation: “Thus, methanogenic archaea might participate in such polymicrobial diseases through syntrophic interactions, representing one component of a ‘unit of pathogenicity’ in addition to bacterial partners.”  In other words, in infection, microorganisms work together synergistically…while making us sick.
6. There may also be multiple ways archaea directly affect our health. Here’s one example:  methane gas has a physiological effect.  For example, it appears to affect gut motility, potentially leading to constipation.   On the other hand, methane may also be crucial in beneficial processes, such as enhanced exercise capacity, and have anti-inflammatory and neuroprotective effects.  The role played by these archaea has to be studied.
7. Pathogenic archaea have yet to be identified.

To summarize:  “…it is evident that archaea are abundant, diverse and active components of numerous microbiomes in plants, animals and humans.  The current literature indicates that their presence has a substantial influence on their hosts and on other members of the microbiome.   However, it is still unclear whether these interactions rely on archaea-specific traits or on properties shared with and/or acquired from other microbiome components.”  This is a really exciting, brand new field of research that someday, may lead to a vast array of new treatments.  As always, I will stay on top of any new developments!

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[i] Guillaume Borrel et al. The host-associated archaeome, Nature Reviews Microbiology (2020). DOI: 10.1038/s41579-020-0407-y

[ii] https://phys.org/news/2020-08-scientists-probe-role-archaea-human.html