A Tiny Mutation Makes Fish Immune to PCB Poisoning

By Veronique Greenwood | October 31, 2011 12:07 pm

tomcod
Because of two missing amino acids, this tomcod can swim through PCBs—and survive.

PCBs are nasty pollutants—they mess with hormones and have been linked to cancer—but until they were banned in 1977, dumping them in US rivers was a common practice for companies like GE. While plenty of wildlife suffered from ingesting PCBs, some fish in the Hudson and other be-sludged rivers evolved an immunity to the poisons, a intriguing example of quick adaptation that scientists have been watching with interest. A recent Economist article focusing on this research describes the fascinating genetic ju-jitsu that allows fish in the Hudson and in the harbor at New Bedford, MA, to keep themselves alive in PCB-contaminated waters.

PCBs do their damage by binding to a protein called the aryl hydrocarbon receptor, or AHR, thus stopping it working properly. AHR is a transcription factor, meaning that it controls the process by which messenger molecules are copied from genes. These messenger molecules go on to act as the blueprints for protein production, so preventing a transcription factor from working can cause all sorts of problems. Both Hudson tomcod and New Bedford killifish, however, have unusual AHR molecules. And it is this that seems to explain their immunity.

A protein is a chain of chemical units called amino acids. In tomcods, AHR is composed of 1,104 such units. Except that in Hudson tomcod it frequently isn’t. These fish generally have 1,102 amino acids in their AHRs. The two missing links in the chain (a phenylalanine and a leucine, for aficionados) are encoded in the gene for ordinary tomcod AHR by six genetic “letters” that are missing from the DNA found in PCB-resistant Hudson tomcod. The shortened version of AHR does not bind nearly so easily to PCBs. It still, however, seems to work as a transcription factor. The result is fish that are more or less immune to PCB poisoning.

Read more at the Economist.

Image courtesy of Mark Mattson, Normandeau Associates, Inc. / Woods Hole Oceanographic Institute

CATEGORIZED UNDER: Health & Medicine, Living World
  • http://oto-env.com/blog Jim Okun

    Could you please provide a citation to a scientific study that supports your statement that “plenty of wildlife died from ingesting PCBs”? Since Discover presents itself as a scientific based magazine, supporting your claims should be part of writing up articles.
    Thanks.

  • Sam

    This reminds me of when we tried to eliminate malaria, the mosquito reproduced so quickly that it only took one to save the entire race. when you think about evolution it is pretty clever (or should I say lucky) it uses a brute force method for survival and this is exactly why its so effective and I suppose… why we’re still around today.

  • Amos Zeeberg (Discover Web Editor)

    @Jim: We can’t put in scientific references to everything in every article—it’d take too long and make the articles unwieldy. But since you asked, I just did a quick search for articles on PCBs and fish mortality. Here are a couple results:

    Great Lakes embryo mortality, edema, and deformities syndrome (GLEMEDS) in colonial fish-eating birds: similarity to chick-edema disease.
    http://www.ncbi.nlm.nih.gov/pubmed/1875430

    Egg mortality of lake geneva charr (Salvelinus alpinus L.) contaminated by PCB and DDT derivatives
    http://www.springerlink.com/content/x450033740223j20/

  • http://oto-env.com/blog Jim Okun

    Amos – Thank you for making the effort to locate the two citations. The first one actually addresses harm caused by DDT (and it metabolites DDE and DDD) and does not directly speak to harm to wildlife from PCBs, it only speculates on possible harm. The second is a laboratory study where fish were exposed to PCBs in an experimental setting; so this again does not document harm to wildlife.

    It is my general impression that PCBs have gotten a very bad reputation, but when you look at the science of how dangerous they really are, there is not much to support the exaggerated claims. PCBs just got lumped in to the highly dangerous category based on incomplete or erroneous scientific studies.

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