7th Activity: Fartin' Microbes

posted Aug 23, 2010, 3:44 AM by Beth Orcutt
Greetings, microbe adopters! We hope that you all had a great weekend, and that you are enjoying the start of a new school year. Our research cruise has another two weeks to go before we head back to Victoria, Canada. The scientists are very busy preparing for another CORK installation and more sediment and rock coring. 

This week’s adoption activity is all about fartin’ microbes! Before you turn up your nose, have no fear – while some of the following information will explain to you the science of gas production, there is no human farting required in making this activity work!! 

First, a little background - When some microbes eat sugars and other organic material, they generate different gases as waste products. These gases can include carbon dioxide, hydrogen, methane, gaseous alcohols like ethanol and methanol, hydrogen sulfide and other sulfurous compounds (which smell like rotten eggs), and gaseous fatty acids like acetic acid (what vinegar smells like), formic acid (the stuff that makes ant bites sting), and butyric acid (really stinky stuff that kind of smells like throw-up – yuck!). In humans and other animals, the gases that your gut microbes make from eating up sugars contribute to the gas released in flatulence (a.k.a. farts, although the majority of fart gas is actually swallowed air, or, in the case of soda drinkers, the swallowed fizzy carbon dioxide bubbles). Contrary to popular belief, the methane gas in farts is odorless! Most of the smelliness of farts actually comes from the gaseous sulfur compounds that are generated from food digestion. Some foods, like cauliflower, eggs and meat have more sulfur compounds in them, so they lead to stinkier farts. 

What does this have to do with the microbes from the deep dark ocean that you have adopted?!? Well, in a similar style to the microbes in your guts, some microbes living in the deep dark ocean also generate gas. For instance, the adopted microbes Methanococcus and Methanopyrus both generate methane gas, and Desulfovibrio makes stinky hydrogen sulfide gas from all of the sulfate that it eats. We like to think of this gas production as “microbe farts” :) 

During our research expedition, some of the scientists have deployed special gas samplers down into the ocean crust to analyze which kinds of gas are found down there, and how concentrated the gases are. You can learn all about those samplers in the recent Giant Microbe Video about OsmoSamplers. While a lot of the gases in the hard oceanic crust are produced during the hydrothermal interaction of the fluids and the rocks, some of the gases might also come from fartin’ microbes! By analyzing those gas samples, the scientists will hopefully get a better idea of which types of microbes are living down in the oceanic crust by the types of gases that are generated. It’s kind of similar to someone guessing what you ate for dinner by the smell of your farts! 

As promised, though, this week’s activity isn’t about your farts. Instead, we will use some hardy yeast microbes to examine gas production. Yeast – the stuff that you need for making bread and other fermented products – are actually microscopic eukaryotes. They are different from the microbes you have adopted, which are all bacteria or archaea, because they actually have a cell nucleus like animal and plant cells. Because of their tiny size, we’ll consider them to be honorary “microbes” for this activity :) 

The purpose of this week’s activity is to examine the amount and type of gas that yeast makes when it grows on different sugars. 

What you’ll need: 
  • measuring spoons (1/8 teaspoon, 1 teaspoon) 
  • about 1 teaspoon of dry yeast (you can find this in the baking section of the grocery store) 
  • about 1 tablespoon of sugar 
  • a small vessel with a narrow mouth for holding about 2 teaspoons worth of liquid – common things you might have around the house that would work include empty travel-size lotion or shampoo bottles 
  • A few balloons 
  • A few rubber bands 
  • Some electrical tape 
  • Some water 
  • A marker 
  • An oven set to 120-160 degrees Fahrenheit, and a baking dish 


1) Check that your balloon will fit around the opening of your small vessel. 

2) Inside your small vessel, mix 1/8 teaspoon of sugar with 2 teaspoons of water. Then add 1/8 teaspoon of dry yeast. Mix well. 

    a. Variation: Instead of adding simple sugar water to your vessel, you could also try filling a vessel with fruit juice. 

3) Carefully attach the balloon to the top of the vessel, trying to keep the balloon as air-free as possible. Use a rubber band to hold the balloon tightly in place, then wrap some electrical tape around the base of the balloon to attach it tightly to the bottle. This will help any gas from leaking out. 

4) Place your balloon and bottle into the baking dish and place it all in the oven. The yeast become activated once they warm up to about 120 degrees Fahrenheit. As the yeast spring into action and begin eating the sugar, they will start to generate carbon dioxide and other gases – and the balloon should slowly start to fill up. 

5) After 2 hours, check on your balloon – has it started to fill up yet? Gently shake up the bottle to remix the yeast. 

6) Take a picture of your balloon on the bottle. 

7) After 2 more hours have gone by, check on your balloon again – does it seem any bigger now? 

8) Carefully remove the balloon from the vessel and then gently squish out some of the gas trapped inside to do a smell test. Record what you think it smells like. If you used different sugars/juices – how do the smells compare? 

9) Please send an email by Thursday, 26 August, 2010 with a picture of your yeast balloon and a few sentences about what your yeast farts smelled like and if there was any differences in smell depending on which sugars were used.