Archaea in and on the Human Body: Health Implications and Future Directions

Although they are abundant and even dominant members of animal microbiomes (microbiotas), from sponges and termites to mice and cattle, archaea in our own microbiomes have received much less attention than their bacterial counterparts. The fact that human-associated archaea have been relatively little-studied may be at least partially attributed to the lack of any established archaeal human pathogens [1,2]. Clinically oriented microbiology courses often do not mention archaea at all, and most medical school and biology students are only aware of archaea as exotic extremophiles that have strange and eukaryotic-like molecular machinery. Since archaea have been known to be associated with the human gut for several decades, one would think that human microbiome studies may unravel new facets of archaea–human interactions. However, adequate universal primers that amplify both bacterial and archaeal small 16S rRNA genes but not any host rRNA genes were only published in mid-2011 [3], and thus, many studies chose to focus on bacteria alone rather than multiply effort and expense to cover taxa that are considered secondary in importance, if not altogether rare. Here, we provide a brief overview of what is currently known about archaea in and on the human body and their potential effects on human health (for additional reviews on archaea and their potential involvement in human disease, see [4–8]).