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Overview | In this lesson, students learn about how and why scientists are studying the biodiversity of previously unexplored places, such as the insides of homes and the surface of the human body. They then sample the microbes living in their own belly buttons and consider the implications of this newly discovered microbial diversity.



Materials | Computers with Internet access, sterile spreaders, sterile swabs or new box of Q-tips, tryptic soy agar plates (for a more economical approach, you may instead prepare your own plates ahead of time), micropipettor (that can measure 20 microliters) and corresponding plastic tips or disposable transfer pipette, 10 percent phosphate buffered saline solution, microcentrifuge tubes, sterile spreaders or glass beads, 70 percent ethanol, paper towels, permanent markers and tape.

Warm-Up | Ask your students what kinds of organisms, other than people, live in their homes with them. If students only offer examples of pets, such as dogs or cats, prompt them by asking about invertebrate animals they might have seen, such as insects or spiders. Where have they seen them? Where else in their homes do they think they might find invertebrates hiding? Jot their answers on the board, then ask them how many different species of invertebrates they think might live in their homes; record these responses on the board as well.

Next, have your students take the “The Bugs in Your Home” quiz. Talk about the quiz in the context of students’ own lives. What surprised them about the indoor habitats of some of these organisms? Have they heard of any of these organisms?

Then, have your students read “The Bugs in our Homes,” which highlights research on the arthropods — insects, spiders and their relatives — living in a sample of 50 homes in Raleigh, North Carolina. Ask students: Were they surprised to learn that many homes in the study had over 100 different species of arthropods living in them? What does this story, and this research, tell us about biodiversity? Wrap up by talking about the other kinds of organisms — not just animals, but also bacteria, fungi and archaea — that researchers have found in our homes and on our bodies, once they started to look for them.

Related | In the Times Matter column “The Great Indoors: The Next Frontier,” Carl Zimmer explores the largely unknown biodiversity and ecology of the organisms that live inside our homes:

When humans began building shelters about 20,000 years ago, we unrolled a welcome mat for other species. Over the past few thousand years, the indoor biome has grown to colossal proportions as cities and suburbs spread across the continents. More recently elevators and other technology have lifted the indoor biome into the sky. We humans are whittling down coastal wetlands, tropical forests and other biomes. But not the indoor biome: Globally, it’s already more than 247,000 square miles, bigger than France and growing rapidly. Ours is a biome with a future. And yet the indoor biome remains at science’s frontier. “We know virtually nothing about it,” said Laura J. Martin, an ecologist at Cornell University.

Read the entire article with your class, using the questions below.

Questions | For discussion and reading comprehension:

What is the “indoor biome?” Why has it been so little studied until now? In the article, Mr. Zimmer writes, “It’s possible that some species already were adapted for living indoors when they first turned up on our doorsteps.” Name two species found in many homes, and identify the features that make these organisms adapted to life indoors. In what ways are our homes similar to caves? How are some of the organisms that inhabit homes similar to those in caves, and how are these traits advantageous to the organisms in each setting? Jack Gilbert, a research scientist at Argonne National Laboratory, says that in the future, it might be possible to design and engineer homes to keep out pathogens. How might this be possible? Is it necessarily a good idea to keep all microbes out of our homes? Why or why not?

Activity

Note: In advance of this activity, prepare one microcentrifuge tube containing 0.5 milliliter of 10 percent phosphate buffered saline solution for each student.

One of the most fascinating aspects of current research into the indoor biome and the human microbiome is the vast number of species scientists have found, and continue to find, that are completely new to science. It is this discovery of the unknown that pushes scientists to search for microbes in new and unexplored places.

In this activity, students replicate some of the work these scientists are doing to better understand what lives with us in our homes, our schools, our hospitals, our transportation systems and even on our bodies. Students will sample microbes living in their belly buttons in an experiment modeled after The Belly Button Biodiversity Project, a citizen science project conducted by Rob Dunn, an associate professor in the Department of Biological Sciences at North Carolina State University, and his colleagues that sampled the belly buttons of hundreds of volunteers.

As a class, watch the video “Belly Button Biodiversity,” and then ask the following questions:

What do Robert Dunn and his research group hope to learn by sampling the microbes that live in the belly button? What are possible roles that microbes living on human skin play? What questions do you have about this video?

Then, explain to students that they will replicate the Belly Button Biodiversity Project in your class. Have students:

Wipe down their stations with ethanol. Distribute the materials and have students put on gloves, write their names on the bottom of their agar plates, and set their micropipettes to 20 microliters;

Open the swab and swirl it around in their belly buttons three times, using constant pressure;

Swirl the swab in the phosphate buffer for 10 seconds, then cap the vial and shake it gently for 10 seconds;

Place a new tip on the micropipettor and draw up 20 microliters of the phosphate solution. If using a disposable pipette, place 2 drops on the plate;

Squirt the solution slowly onto the agar;

Carefully spread the solution around the plate using either sterile glass beads or a sterile spreader;

Cover the plate, tape the top and bottom together, and place the plate on a heating pad upside down (so the agar is on the top), or, if you have access to one, an incubator.

Leave the plates incubating for two days at 37 degrees Celsius. After two days, have students retrieve their plates and record the following observations:

How many colonies are on the plate?

How big are the colonies?

What color and shape are the colonies?

What other observations can you make — can you describe the colonies’ texture? Do they have clearly defined edges, or margins?

Have students trade with a partner and make the same set of observations. Ask: How are their plates similar? How do they differ?

When students have finished, talk about their results in the context of biodiversity. How many different types of colonies did they see on their plates? Did they see similar types of colonies on their partners’ plates? Then, show them the images of the four most common microbial types identified in the Belly Button Microbiome Project, and ask them if they can classify any of their colonies as one of these types. What characteristics of the colonies on their plates led them to this conclusion?

[The above protocol is adapted from the Belly Button Biodiversity Lab by Students Discover and yourwildlife.org.]

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Belly Button Alternatives: If you think your students might not be comfortable with swabbing their belly buttons, or as a possible extension activity, have them collect samples from locations around the school, following the above protocol. If you choose to do this, have a quick discussion, asking the following questions:

Which surfaces in the school would you expect to harbor the highest level of microbe diversity? Why?

Which would you expect to have the lowest level? Why?

Why do most of us only get sick a few times a year if microbes are living on every surface we encounter?

To wrap up, circle back to the beginning of the lesson and Carl Zimmer’s article about the indoor biome. Given what students have learned, what are some places in their homes students might like to explore for microbial diversity? Why, and what do they expect to find there?

Extending the Conversation: You may choose to extend the conversation further by reading more about the human microbiome. How many different species make up our microbiome, and why have they been rarely studied until now? What is the Human Microbiome Project, and what were some challenges researchers in the project faced when looking for volunteers from whom to sample bacteria?

Then, talk about how all of this microbial diversity interacts with or otherwise affects us:

Ask students to provide at least three specific examples of ways in which our microbiome positively affects our health. Conversely, what are some possible consequences of disrupting the microbiome? For example, high levels of antibiotic use may predispose children to developing allergies and asthma. How does the human body differentiate between beneficial microbes and pathogens? That is, how does the immune system “know” not to attack helpful microbes? [If students struggle with this question, point out that scientists actually don’t have a solid understanding of this yet — one of many questions that remains to be answered by exploring the human microbiome.]

Going Further

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1. Participate in a Citizen Science Project: Your class might participate in a currently running citizen science project that aims to better understand the indoor biome, the ecology of the organisms living on our bodies, or microbes in our environment. Your Wild Life at North Carolina State University currently has studies underway that aim to better understand what lives in armpits and on your face; the start-up company uBiome has citizen scientist kits that allow people to sample their own microbiomes; and SciStarter hosts a searchable database of citizen scientist projects across the country.

2. Express the Joy of Discovery: In Invisible Life, Robert Dunn writes about Antonie van Leeuwenhoek, one of the first scientists to document the existence of microbes:

What really marked Anton was not the specifics of what he saw but the avidness with which he saw it, the joy with which he greeted the life around him, tiny life, unknown life, life of near infinite possibilities, a shimmering diversity of mystery in every swab of spit or emulsion of pepper. I bring the story of Anton up here because we are, right now, for the first time since Anton, in a time in which scientists are, joyously, using their tools to study the life around us. Dozens of scientists are now, like Anton, standing in their living rooms and kitchens awe-struck by what they are seeing as they study their (and our) daily lives (even though they are not quite seeing it). Unlike Anton, modern scientists study the small life-forms around them by studying their genes. We can wipe a swab across your tongue to collect the cells of the tiny life-forms living in your spit. By breaking open the cells, we can examine the genes of those creatures and within a few days even determine who exactly is living there. What we are finding is thousands of species on your body, even more thousands around the house and even more thousands in the backyard. Just 3000 species of bacteria are named and yet in a single study of just nine habitats in houses we found 8000 species, most of them without names. I will not very boldly speculate that there are more unnamed species of microbes in a single house than there are named species in the world.

Have you ever thought about science as being “joyful?” Why or why not? Why do you think scientists today would be “joyously” studying the life around them? Choose one of the narratives listed in the table of contents on Invisible Life, and show how the authors share their joy in discovery and learning. How do many use the tools of storytelling — descriptive language, plot and metaphor — to reflect their enthusiasm for their subjects? Could looking at science from the perspective of joyful discovery change how people view science?

Then, reflect on a time when you have experienced the joy of discovery, perhaps even in exploring your own belly button’s microbiome. What words would you use to describe how you felt? What was your discovery? Write your own narrative essay detailing your scientific experience, and then share your work with your classmates in some way – through a live reading or gallery walk, or by publishing them on a class website.