Chapter 14, Problem 8P

Recently, scientists tested the possibility that human gut bacteria may play a role in determining body weight.

The study subjects were four sets of twins (one set of identical twins and three sets of fraternal twins), where one twin was of normal weight and the other was obese. Samples of their gut bacteria were collected and transplanted into bacteria-free mice. Mice with the different bacterial transplants were all fed the same diet and monitored over the course of about one month. For each of the four twin pairs, the mice with the bacteria from the obese twin gained significantly more weight and fat than the mice transplanted with the bacteria from the normal twin.

a.	What would you conclude about the relationship between the human gut microbiome and body weight?
b.	Why were twins used in the study?
c.	Do the results of this study mean that human genes (genes in the nuclei of human cells) do not play a role in body weight and fat content? Explain.
d.	Mice are coprophagic, meaning that they eat feces. How could you test whether a certain bacterial species associated with leanness or obesity could successfully invade the gut microbiome of an animal in which that bacterial species was not previously found?
e.	One problem with using bacteria-free mice in experiments such as this is that the mouse gut is not equivalent to the human gut as a bacterial host: Different bacterial species thrive in mice and humans. Explain how this fact could affect the experiment discussed in this problem.