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Project Abstract

Ionizing radiation and radiation pollution is an important environmental problem that affects many. It affects those working around radiation facilities, as well as, those who are exposed to it due to widespread nuclear disasters such as those at the Fukushima Daiichi nuclear reactor or the Chernobyl reactor. Penn State’s team project will focus on using a genetic circuit introduced into E. coli bacterial cells, in order to rapidly detect and report the presence of harmful ionizing radiation. We are working to develop a robust and reliable biosensor which utilizes the lambda phage lytic-lysogenic switch coupled with a fast-acting reporter capable of producing an easily visible effect. We believe that the final construct may have the potential to rival current radiation detection methods, such as digital dosimeters.
Our hope is that the basis of our biological dosimeter system will prove to be an effective genetic system capable of detecting harmful levels of radiation and relaying it to those working in the field or an affected area. We envision our system to not only be useful in such applications, but also be capable of further expansion and evolution through the expanding field of synthetic biology.

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Design

Our project focuses on detecting the degradation and damage of DNA associated with ionizing radiation. The initial proposed design is shown below. It consists of two parts: a sensor based on a lambda phage bistable switch, and a fast-acting reporter similar to the reporter designed by the Imperial College of London 2010 iGEM team. Additionally a modified version of the RecA protein is introduced into the system in order to provide efficient activation of the sensor circuit.

Many of the genes for detecting radiation used in this bacterial system have homologous counter-parts in Eukaryotic cells. For instance the RecA protein used in our system is part of a larger family of strand-exchange proteins involved in homologus recombination and DNA repair. Some other examples of this family include the Eukaryotic proteins Rad51 and Dcm1. For this reason it can be thought that a system similar to ours could one-day be used in self-replicating in vivo biosensors for radiation pollution bioremediation purposes and other important applications.

Click below to view more about each part of our project

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Team

Mike Speer

Graduate Student

Dr.Tom Richard

Advisor
Professor of Agricultural and Biological Engineering

Dr. Howard Salis

Advisor
Assistant Professor of Agricultural Engineering

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Brainstorming

In the first few days of summer, we began discussing ideas for our project. Some of our first initial thoughts were to modify bacterial photosynthesis using the BCHM gene or to engineer a serotonin sensor. We thought about making a bacterial fuel cell by using Geobacter as a sacrificial anode. We also liked the idea of using bacteria to perform intelligent tasks, like mathematical arithmetic. The last idea we developed was to engineer a bacteria that would be able to detect radiation. The team spent a few days researching these topics to determine how plausible they would be and after a few days of background research unanimously agreed upon the bacterial radiation detector. As we dug deeper into our topic we narrowed our focus. We discovered that the Penn State 2007 iGEM team had used the lambda phage system to also develop a bacteria that would test for radiation and thought this would be a great area to expand. They were not able to fully assemble their device or test it so we came to the conclusion that we could build upon their initial foundation and develop a great project.

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Research

After deciding to follow up on the bacterial dosimeter idea for our project, we as a team we had to first do some research on the effects of ionizing radiation in order to better determine what exactly we would be detecting.

Currently all living organisms are exposed to a relatively low dose of radiation; this amount is so negligible that the negative effects are unnoticeable. The problem with ionizing radiation occurs when one is exposed to a high dose for a short period and/or low doses over an extended period of time. The International Commission on Radiological Protection (ICRP) recommends nuclear industry employees to limit ones yearly exposer to 50 mSv, or 100 mSv over 5 years.¹ One international study, composing 15 countries and encompassing 598,068 nuclear industry workers, found that an increased risk of cancer exists. Specifically, 99% of those tested were exposed to less than 50 mSv of radiation per year, and 1-2% of these cancer related deaths may be attributable to this exposer. It’s also estimated that 100 mSv of cumulative radiation exposer would result to a 5.9% increase chance of mortality. Therefore it is important to be aware of exposure to radiation especially when working in a nuclear facility or when exposed unintentionally.²


1. Cardis, E. "Risk of Cancer after Low Doses of Ionising Radiation: Retrospective Cohort Study in 15 Countries." Bmj 331.7508 (2005): 77. Print.
2. Shapiro, B. "1990 Recommendations of the International Commission on Radiological Protection." European Journal of Radiology 15.1 (1992): 93. Print.

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Acknowledgments

All work and research was performed by members of the Penn State 2011 iGEM Team under the direction of Mike Speer, Tom Richard, and Howard Salis. We would like to thank the following sponsors of our team:

Affymetrix
Life Technologies
Penn State Institutes of Energy and the Environment
Huck Institutes of Life Sciences