How to Train Your Shewanella

Katherine Mateos, Carleton College

The Approach: In my previous post, I introduced my project, investigating the role of Antarctic bacterium, Shewanella BF02, in the cycling of volatile organic sulfur compounds (VOSCs). 

Sterile technique in action Photo Credit: Peter Lee

The first order of business in this effort is keeping the Shewanella alive and happy. In order to do this in the lab, I make a liquid (known in the biology world as “medium”) for the Shewanella to live in. Our medium is designed to resemble Blood Falls in chemical makeup. In particular, it is very salty, and contains iron and sulfate. I am also careful to remove all the dissolved oxygen in the medium, since the Blood Falls water has very little oxygen. In my medium, I am also careful to keep out any bacteria other than my Shewanella. Since microbes are everywhere, including in the air, on my skin, and on the lab bench, I  use a special set of techniques to avoid unwanted bacteria from infecting my samples. 

Membrane Inlet Mass Spectrometer

Once we have a perfect mix of chemicals for Shewanella, I also add my target organic sulfur compounds. Because I want to see if Shewanella changes these added compounds, I keep track of them using a technique called isotope labeling. Isotope labeling is a clever trick, where the target compounds are tagged with atoms that are the tiniest bit heavier than the ones that we usually see. If Shewanella make the labeled compounds into the VOSC products that I am interested in, those products will also have the same tag, making it easy to identify them.

To identify the tiny differences in mass between tagged and untagged molecules, I use a piece of equipment called a mass spectrometer. A mass spectrometer works kind of like a scale and can determine the mass of each molecule. This allows me to detect isotopically labeled VOSC products. If I see isotopically labeled products, I can be pretty sure that the Shewanella are cycling the labeled compound that I added to their medium. 

Thank you to my mentor, Dr. Peter A. Lee, and our collaborators, Dr. Jill Mikucki and Abigail Jarratt, for their guidance in the research process. This project is supported by the Fort Johnson REU Program, NSF DBI-1757899.

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