Humans in the developed world spend more than 90
percent of their lives indoors, where they breathe
in and come into contact with trillions of life
forms invisible to the naked eye: microorganisms.
Buildings are complex ecosystems that are an
important source of microbes that are good for us,
and some that are bad for us. What determines the
types and distributions of microbes indoors?
Buildings are colonized by airborne microbes that
enter through windows and through mechanical
ventilation systems. And they are brought inside
by humans and other creatures. The fate of
microbes indoors depends on complex interactions
with humans, and with the human-built environment.
And today, architects and biologists are working
together to explore smart building design that
will create healthy buildings for us.
We spend an extraordinary amount of time in
buildings that are extremely controlled
environments, like this building here --
environments that have mechanical ventilation
systems that include filtering, heating and air
conditioning. Given the amount of time that we
spend indoors, it's important to understand how
this affects our health. At the Biology and the
Built Environment Center, we carried out a study
in a hospital where we sampled air and pulled the
DNA out of microbes in the air. And we looked at
three different types of rooms. We looked at rooms
that were mechanically ventilated, which are the
data points in the blue. We looked at rooms that
were naturally ventilated, where the hospital let
us turn off the mechanical ventilation in a wing
of the building and pry open the windows that were
no longer operable, but they made them operable
for our study. And we also sampled the outdoor
If you look at the x-axis of this graph, you'll
see that what we commonly want to do -- which is
keeping the outdoors out -- we accomplished that
with mechanical ventilation. So if you look at the
green data points, which is air that's outside,
you'll see that there's a large amount of
microbial diversity, or variety of microbial
types. But if you look at the blue data points,
which is mechanically ventilated air, it's not as
diverse. But being less diverse is not necessarily
good for our health. If you look at the y-axis of
this graph, you'll see that, in the mechanically
ventilated air, you have a higher probability of
encountering a potential pathogen, or germ, than
if you're outdoors.
So to understand why this was the case, we took
our data and put it into an ordination diagram,
which is a statistical map that tells you
something about how related the microbial
communities are in the different samples. The data
points that are closer together have microbial
communities that are more similar than data points
that are far apart. And the first things that you
can see from this graph is, if you look at the
blue data points, which are the mechanically
ventilated air, they're not simply a subset of the
green data points, which are the outdoor air.
What we've found is that mechanically ventilated
air looks like humans. It has microbes on it that
are commonly associated with our skin and with our
mouth, our spit. And this is because we're all
constantly shedding microbes. So all of you right
now are sharing your microbes with one another.
And when you're outdoors, that type of air has
microbes that are commonly associated with plant
leaves and with dirt.
Why does this matter? It matters because the
health care industry is the second most energy
intensive industry in the United States. Hospitals
use two and a half times the amount of energy as
office buildings. And the model that we're working
with in hospitals, and also with many, many
different buildings, is to keep the outdoors out.
And this model may not necessarily be the best for
our health. And given the extraordinary amount of
nosocomial infections, or hospital-acquired
infections, this is a clue that it's a good time
to reconsider our current practices.
So just as we manage national parks, where we
promote the growth of some species and we inhibit
the growth of others, we're working towards
thinking about buildings using an ecosystem
framework where we can promote the kinds of
microbes that we want to have indoors. I've heard
somebody say that you're as healthy as your gut.
And for this reason, many people eat probiotic
yogurt so they can promote a healthy gut flora.
And what we ultimately want to do is to be able to
use this concept to promote a healthy group of
There are no notes for this quiz.