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From 2012hs.igem.org

eCOlfactory: An olfactory test for the detection of carbon monoxide

According to the National Conference of State Legislatures [1], 25 states have statutes requiring residential carbon monoxide detectors. Currently, the common household CO detectors sold on the market are only sound-based. However, as people age, their senses become less acute. We are investigating the development of a genetic circuit for an indole-free E. coli chassis that converts the odorless carbon monoxide into an indole output - the naturally produced smell of bacteria. Coupled with the common household detector, we might be able to greatly reduce the number of CO-related deaths. Our cell could help save even more lives with another sensory warning of the hidden danger.

A colorless, odorless, and soundless killer takes the lives of nearly 2,100 unsuspecting United States citizens every year; that translates to an average of three people every day. Carbon monoxide poisoning is the leading cause of unintentional poisoning deaths in the United States, and one in every 2,400 people falls victim to CO poisoning, unaware of the invisible attacker. People over the age of 65 have the highest risk of falling victim to this silent killer [2]. Only by being aware of the grave danger, and understanding the structure and function of this gas, we can create a circuit that produces a scent to CO and a warning before it's too late.

The mechanism for CO detection in our system is derived from the bacterium Rhodospirillum rubrum that naturally metabolizes CO as an energy source. This photosynthetic bacterium accomplishes this task in the following chemical reaction: CO + H2O --> CO2 + H2

The enzyme carbon monoxide dehydrogenase (CODH) is a peripheral membrane protein that carries out the primary oxidation of CO to CO2 and then passes the products through a ferredoxin-like sub-unit. R. rubrum also has a carbon monoxide-sensing protein called CooA that activates the gene expression of oxidation enzymes. In our research of R. rubrum, we found that a Turkey iGEM team in the 2010 college division developed CooA and CooA-responsive promoter BioBricks they wanted to make to transform into E. coli. They were able to successfully build these parts, and now our goal is to try and put them into our own genetic circuit that, in the presence of carbon monoxide, will output an unpleasant warning smell.