Biology Now, 2e

Navel Gazing ■ 271

Rob Dunn is an applied ecologist at North

Carolina State University. His fascination with

species around us in our everyday lives has led

him to research projects on microbes in our belly

buttons, armpits, homes, and more.

ROB DUNN

Archaea likely split from Eukarya much later,

around 2.7 billion years ago. The microbes that

make up Bacteria and Archaea display many

small but significant differences in their DNA,

plasma membrane structure, and metabolism.

They also share several important characteris-

tics and so they are traditionally lumped under a

common label: prokaryotes.

Prokaryotes are single-celled organisms,

with a single loop of DNA floating free in the

cytoplasm of the cell (review Figure 4.8 for a

comparison of prokaryotic and eukaryotic cells).

Unlike cells found in the Eukarya, prokary-

otes do not have membrane-enclosed organ-

elles. Prokaryotic cells are not only simpler

than eukaryotic cells; they are smaller—almost

exclusively microscopic, and invisible to the

naked eye because of their diminutive size. The

simple structure and single loop of DNA enable

prokaryotes to reproduce at a much more rapid

rate than eukaryotes, doubling in number every

10–30 minutes (Figure 15.3).

Prokaryotes in both domains are widespread

and extremely abundant, and they display an

astonishing diversity in metabolism. The vast

majority of life on Earth is single-celled and

prokaryotic. Scientists estimate that the number

of prokaryotes on Earth is about 5,000,000,000,

000,000,000,000,000,000,000 (5 nonillion, or

5 3 1030 ). For example, prokaryotes—not fishes

or algae—are the most abundant organisms in

the open ocean, where they play a crucial role in

the ecology of our biosphere.

The success of prokaryotes is due in part to

how quickly a prokaryotic population repro-

duces, and also to the fact that they can live

practically anywhere, including many places

where few other forms of life can, such as deep,

hot thermal vents or the acidic environment of

the human intestine. Humans are saturated in

microbes. We are each a zoo.

Menninger was so intrigued by Dunn’s proj-

ect that when a job became available in his lab

a few months later, she immediately applied for

and got the position. By then, the team had gath-

ered about 60 swabs at local events, including

the aforementioned conference, and now they

had bigger ambitions: Dunn hired Menninger

to spearhead a massive public outreach effort to

acquire belly button swabs from all around the

country. In citizen science projects such as this,

the public participates in research by collecting

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Generation

Population

Q1: If an individual prokaryote divides every 20 minutes, how many

individuals will there be after an hour?

Q2: If the generation time is 20 minutes, how much time will have

gone by when the final generation shown has doubled?

Q3: Many bacteria are able to reproduce more quickly in warmer

conditions. What does this suggest to you about the importance of

refrigerating foods?

Figure 15.3

Prokaryotes are capable of extremely rapid population growth

An individual prokaryote is able to divide in two within 10–30 minutes. Those

two can each divide in two in the same amount of time. This means that even

a single bacterium or archaean can become a large population in a very short

period of time.

and sometimes even analyzing data in cooper-

ation with professional scientists (Figure 15.4).

“At the time, we were right at the forefront

of an explosion in research, learning about how

important the microorganisms that live on and in

our bodies are to our health and well-being,” says

Menninger. “And this was a really great project

to get people talking about the skin microbiome.”