1st Student's Major

Biological Sciences

1st Student's College

Science, Engineering and Technology

Students' Professional Biography

Peter Weber grew up in LeCenter, MN and graduated from LeCenter Highschool in May of 1999. He started attending Minnesota State University, Mankato in the fall of 1999. He is currently majoring in Microbiology with a minor in Chemistry.

Mentor's Name

Dorothy Wrigley

Mentor's Email Address


Mentor's Department

Biological Sciences

Mentor's College

Science, Engineering and Technology


Nisin is a peptide that is made by the bacterium Lactococcus lactis. Nisin is a small molecule that kills gram positive bacteria by binding to their membrane and by disrupting the proton motive force. When food is processed it is heated to kill bacteria, but some bacteria still survive. Adding nisin to the food provides a second barrier for the growth of the bacteria. Purified nisin has become quite expensive in the current marketplace. Therefore this study is directed at producing nisin and purifying it. L. lactis was grown in five different media (BHI, BHI + 1% glucose, BHI + 1% sucrose, BHI + 3% yeast extract, and skim milk medium). Samples of nisin from these media were filter-sterilized and tested for their ability to inhibit the growth of Lactobacillus viridescens, which is susceptible to nisin. It was found that nisin from the media BHI + 3% yeast extract after 8 hours of growth has a similar concentration as the standard, which was 1000 μg/ml. The nisin was then purified. An extraction process using ammonium sulfate was used to precipitate nisin out of the media. It was found that a 50% ammonium sulfate concentration precipitated out all of the nisin. The nisin was dialyzed against distilled water to remove the salts. The Minimal Inhibitory Concentration (MIC) of the extracted nisin, using Bacillus cereu and endospores was equivalent to a commercial nisin preparation at 1000μg/ml.

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.