An excellent educational series entitled ‘Intimate Strangers:
Unseen Life on Earth’ was recently aired on public television
in the US (see [1]). The series was designed to introduce
viewers to the world of microbiology, and emphasized the
diversity of microbial life, pointing out many ways in
which the activities of microbes in the global biosphere,
and their impacts on human health, remain poorly understood.
Two papers [2,3], published about the same time as
the series was being shown, drive home the concept of
microbes as ‘intimate strangers’ to humankind. Comparative
analysis of amplified 16S ribosomal RNA sequences
was used to examine bacterial diversity in the subgingival
crevice in the mouth [2], and in human feces [3]. The
results show that the microbial communities we all carry
within us contain many unrecognized bacterial species,
perhaps comprising the bulk of these populations. So
despite the fact that the human commensal flora has been
studied for many decades, we clearly still have a lot to
learn about it. Fortunately, this work also suggests
approaches to characterizing the structure and dynamic
behavior of these microbial communities, and ultimately
understanding their ecology.