- Where do Halobacteria live?
Finding a Link Between Archaea and Disease
Archaea are not known to cause any disease in humans, animals, plants, bacteria, or in other archaea.
Although this makes sense for the extremophiles, not all archaea live in extreme environments. Many genera
and species of Archaea are mesophiles, so they can live in human and animal microbiomes, although they
rarely do. As we have learned, some methanogens exist in the human gastrointestinal tract. Yet we have no
reliable evidence pointing to any archaean as the causative agent of any human disease.
Still, scientists have attempted to find links between human disease and archaea. For example, in 2004, Lepp
et al. presented evidence that an archaean calledMethanobrevibacter oralisinhabits the gums of patients with
periodontal disease. The authors suggested that the activity of these methanogens causes the disease.[28]
However, it was subsequently shown that there was no causal relationship betweenM. oralisand periodontitis.
It seems more likely that periodontal disease causes an enlargement of anaerobic regions in the mouth that
are subsequently populated byM. oralis.[29]
There remains no good answer as to why archaea do not seem to be pathogenic, but scientists continue to
speculate and hope to find the answer.Summary
4.1 Prokaryote Habitats, Relationships, and Microbiomes
- Prokaryotes are unicellular microorganisms whose cells have no nucleus.
- Prokaryotes can be found everywhere on our planet, even in the most extreme environments.
- Prokaryotes are very flexible metabolically, so they are able to adjust their feeding to the available natural
resources. - Prokaryotes live incommunitiesthat interact among themselves and with large organisms that they use as
hosts (including humans). - The totality of forms of prokaryotes (particularly bacteria) living on the human body is called the human
microbiome, which varies between regions of the body and individuals, and changes over time. - The totality of forms of prokaryotes (particularly bacteria) living in a certain region of the human body (e.g.,
mouth, throat, gut, eye, vagina) is called themicrobiotaof this region. - Prokaryotes are classified into domains Archaea and Bacteria.
- In recent years, the traditional approaches to classification of prokaryotes have been supplemented by
approaches based on molecular genetics.
4.2 Proteobacteria
- Proteobacteriais a phylum of gram-negative bacteria discovered by Carl Woese in the 1980s based on
nucleotide sequence homology.
Micro Connections
- P.W. Lepp et al. “Methanogenic Archaea and Human Gum Disease.”Proceedings of the National Academies of Science of the United
States of America101 no. 16 (2004):6176–6181. - R.I. Aminov. “Role of Archaea in Human Disease.”Frontiers in Cellular and Infection Microbiology3 (2013):42.
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