Team:iTesla-SoundBio/Description

Description

What are PCBs?
Polychlorinated biphenyls (PCBs) are a class of man-made chemicals that contaminate many of the world’s lakes and waterways1. They were originally produced for industrial and commercial applications, and although their manufacture has been banned since the 1970s, these deadly toxins are still present in the environment today, mainly due to bioaccumulation, as well as due to the improper disposal of old electrical equipment. It has been known for several decades that PCBs do eventually break down, but because they are highly nonreactive and resistant to acids, bases, and heat, their rate of decomposition in the environment is slow. The pathway by which they are broken down was only recently discovered. A bacterium called Dehalococcoides mccartyi has been observed to break down PCBs with a variety of enzymes, the genes for three of which (pcbA1, pcbA4, and pcbA5) were sequenced in 2014 by Wang2. The figure below depicts the dechlorinating mechanism of these three genes on PCB and PCE (tetrachloroethene) molecules.



Image courtesy of PNAS2


Why is this an issue?
PCBs are probable human carcinogens, have acute toxic effects, and can cause significant impairment of the immune system and thyroid. They are also known to disrupt hormone functions and generate developmental issues - women exposed to PCBs can give birth to children with significant neurological and motor control problems1. Compared to other waterways, the Washington Puget Sound has a considerably high level of PCBs, which bioaccumulate in organisms over the years. For native predators such as the orca, the biomagnification of PCBs up the food chain has been severely detrimental3.

As stated before, the bacterium Dehalococcoides mccartyi has the ability to dechlorinate PCBs, thereby reducing their toxicity. However, D. mccartyi is an anaerobic species, and can only obtain energy through organohalide respiration. This makes them difficult to work with in terms of practical applications.


What is our solution?
In our project, we aim to transfer pcbA1, pcbA4, and pcbA5 - the genes responsible for producing the PCB-dechlorinating enzymes - into E. coli bacteria. Unlike D. mccartyi, E. coli is able to thrive in aerobic environments such as oceans and waterways, making them a much more suitable species to use in potential PCB cleanup operations. Our end goal is the production of a technology that uses the E.coli-produced dechlorinating enzymes to facilitate PCB cleanup, or the development of a process containing this genetic pathway that can be executed in PCB-contaminated environments.



References:

  1. Hudson River Sloop Clearwater. http://www.clearwater.org/news/pcbhealth.html (accessed August 7, 2017).
  2. Bedard, Donna L. PCB dechlorinases revealed at last. PNAS 2014, 111(33), 11919-11920. http://www.pnas.org/content/111/33/11919.full
  3. B.C. Cetacean Sightings Network. http://wildwhales.org/threats/toxins/ (accessed August 7, 2017).