Biology Now, 2e

Navel Gazing ■ 281

microbes as the bad guys that our bodies were

constantly at war with. But now we recognize that

our ecosystems wouldn’t function without microbes:

we would have no oxygen to breathe, no plants to

eat. And microbes in our gut and on our skin, when

in healthy balance, promote human health.

We emphasize a healthy balance because it is

possible for communities in the human microbiome

to shift out of balance—a phenomenon called dysbi-

osis, which may cause illness. Alternatively, patho-

genic bacteria can make us sick as well. Although

the great majority of bacteria are harmless and

many are actually beneficial to humans, some cause

mild to deadly disease. Interestingly, archaeans are

not known to be pathogens of any organism.

The biodiversity of microbes on our skin actu-

ally helps keep pathogens away. When a danger-

ous microbe lands on your skin, even before

it meets the immune system it meets other

microbes. If the skin has a diversity of microbes,

odds are “one of them has the ability to kick the

butt” of the pathogen, says Dunn.

After the overwhelming response to the

belly button project, the lab kicked off a new

citizen science spectacular: “Armpit-pa-looza”

(Figure 15.12). As with the belly button, the

team began collecting swabs of microbes

living in people’s armpits. In a preliminary

study, the team found that the use of antiper-

spirants or deodorants dramatically inhibits

bacterial growth, affecting the composition

of the microbial populations on the skin more

strongly than any other factor. “It now looks

like one of the biggest things affecting skin

microbes in general is the use of antiperspi-

rant or anti-odor products,” says Dunn.

Now the team is taking a look at microbes on

the skin of dogs. Skin wounds on pet pooches

actually heal about four times faster than human

skin wounds do, says Dunn, and he suspects that

skin microbes are involved. “We’re starting to

figure out if we can predict wound healing rates

as a function of which microbes are there to start

with,” says Dunn. “I’m pretty excited about that.”

Figure 15.12

Sampling armpits for science

Citizen scientists volunteer to have samples taken of the prokaryotes living

under their arms.

● (^) The non-Eukarya, or prokaryotes, fall into two
domains: Bacteria and Archaea.
● (^) All prokaryotes are microbes—microscopic,
single-celled organisms—but the Bacteria and
Archaea differ in significant ways, such as in
their DNA, plasma membrane structure, and
metabolism.
● (^) Prokaryotes can reproduce extremely rapidly and are
the most numerous life-forms on Earth. They also
have the most widespread distribution.
● (^) Many prokaryotes, particularly bacteria, have
specialized structures. Bacteria with a capsule
surrounding the cell wall can avoid detection by

REVIEWING THE SCIENCE

organisms’ immune systems. Short, hairlike pili

help bacteria attach to surfaces and to each other.

Whiplike flagella assist in locomotion.

● (^) Some prokaryotes, particularly archaeans, thrive in
extreme environments. Thermophiles, for example,
live in extremely hot places, and halophiles, in very
salty places.
● (^) Prokaryotes typically reproduce by binary fission,
and they may acquire DNA from each other or their
environment via horizontal gene transfer.
● (^) Some prokaryotes use quorum sensing to
communicate with each other, and some undergo
sporulation for protection.