This is from Elizabeth Pennisi (Science Magazine, 2010)
This past decade has seen a shift in
how we see the microbes and viruses in
and on our bodies. There is increasing
acceptance that they are us, and for
good reason. Nine in 10 of the cells
in the body are microbial. In the gut
alone, as many as 1000 species bring
to the body 100 times as many genes as
our own DNA carries.
Their genes and ours make up a
metagenome that keeps the body
functioning. This past decade we’ve
begun to see how microbial genes
affect how much energy we absorb from
our foods and how microbes and viruses
help to prime the immune system.
The ideas of a microbiome and a virome
didn’t even exist a decade ago. But
now researchers have reason to hope
they may one day manipulate the body’s
viral and microbial inhabitants to
improve health and fight sickness.
From Discover Magazine (2011)
There are 20 times as many of these
microbes as there are cells in the
body, up to 200 trillion in an adult,
and each of us hosts at least 1,000
... a person is not so much an individual
human body as a superorganism made up
of diverse ecosystems, each teeming
with microscopic creatures that are
essential to our well-being.
Two of the largest efforts [to use genetic sequencing to explore how the diversity of the microbiome impacts our health] are the
Human Microbiome Project, funded by
the National Institutes of Health, and
the European Union’s Metagenomics of
the Human Intestinal Tract.
these groups have only just begun to
publish their findings, it is already
clear that the microbiome is much
more complex and very likely more
critical to human health than anyone
To clarify a possible point of confusion, microbial biomass is only a small portion of a human body's mass, due to the small size of bacterial cells relative to human cells.
From San Francisco Chronicle (2012):
The human body carries more than 100 trillion bacteria - up to five pounds of the tiny >single-celled organisms.