Taking a bacterial census

This exercise is a part of Educator Guide: Where Bacteria Live On Our Tongues / View Guide

Directions for teachers: After your students read the online Science News article “Here’s where bacteria live on your tongue cells,” ask them to answer the following questions. A version of the story, “Where bacteria live on our tongues,” can be found in the April 25, 2020 issue of Science News.

1. What does the image at the top of the article show? What do the different colors represent?

The main image shows a single human tongue cell coated in different types of bacteria. The tongue cell is gray, and the types of bacteria are represented by different colors including red, yellow, blue, green and purple.

2. The author says that bacteria on tongue cells build “neighborhoods.” What are bacterial neighborhoods? What literary device is the term an example of?

Bacterial neighborhoods are clusters of different types of bacteria on the surface of human tongue cells. The author’s use of “neighborhoods” to describe these clusters is an example of a metaphor.

3. How did scientists map bacterial neighborhoods on human tongue cells?

Scientists attached differently colored fluorescent markers to each type of bacteria in samples scraped from people’s tongues. Under a microscope, the colors let scientists see where on a cell’s surface different bacteria were found.

4. Paraphrase (restate in your own words) the article’s second paragraph, which describes the main research finding.

On the surface of human tongue cells, various types of bacteria form distinct groups. As these groups grow, they create microenvironments where bacterial species can flourish.

5. How was the distribution of bacteria on different tongue cells similar? Be as specific as possible in terms of bacteria type and location on tongue cell.

The patchwork pattern of neighborhoods was consistent across cells from different samples and people. And three types of bacteria were common across samples: Actinomyces bacteria tended to form groups close to the human tongue cell. Rothia bacteria clustered away from the human cell. Streptococcus bacteria formed a thin outer layer.  

6. How was the distribution of bacteria on different tongue cells different?

The specific type and placement of bacteria differed from cell to cell.

7. Why are scientists interested in understanding bacterial neighborhoods?

Scientists are interested in how groups of bacteria arrange themselves on the tongue because it could shed light on how the bacteria work together to maintain healthy environments — in this case, the environment is a person’s mouth.