'Superbug' - a bacteria that chews up herbicides

The biochemist who brought you oil-eating bacteria is now designing one that chews up herbicide. Theoretically, at least, this could help clean up toxic residues in soil.

Ananda M. Chakrabarty and his colleagues S. T. Kellogg and D. K. Chatterjee at the University of Illinois have developed a genetic engineering technique that has produced a mixture of bacteria that feed on the herbicide 2,4,5-T (used in Agent Orange). Now they hope to produce a pure bacterial strain with that valuable capacity.

Among other things, their work has gotten some good out of Love Canal. Some of the bacteria that contributed genetic material for the herbicide-eaters was recovered from that dump, from a dump at Eglin Air Force Base in Florida, and from one in Arkansas.

Their technique grew out of research done by Chakrabarty at the General Electric Company, where he produced oil-eating bacteria. Whether or not such microbes will one day actually help clean up oil spills remains to be demonstrated. But Chakrabarty made legal history when he was awarded the first patent ever granted for a new microbe - a patent grant later upheld by the Supreme Court of the United States.

This means of helping microbes gain new capacity uses a genetic process that occurs naturally and that genetic engineers are now learning to employ. Bacteria contain some of the genetic material that determines their nature and functions on bodies called chromosomes. When bacteria reproduce by dividing in two, their progeny inherit sets of these chromosomes. Many bacteria, however, also carry genetic material in little circular molecules called plasmids. These reproduce independently of the chromosomes. They too are passed on to daughter cells. But they can also transfer to unrelated bacterial strains and, sometimes, even to different species.

Genes that help microbes eat oil or herbicides reside on plasmids. Explaining their work in Science, the Illinois biochemists note that plasmids can pick up genes from other plasmids to assemble complexes of genetic instructions that give bacteria new capabilities. This is one of the mechanisms that lead to resistance to deleterious chemicals, such as antibiotics, in nature. It gave the Illinois researchers a tool for assembling the genes needed to allow bacteria to feed exclusively on 2,4,5-T.

While this chemical is harmful for humans, it's not toxic to bacteria. Also, its concentration in contaminated soil is too low to be a main food source for microbes. So bacteria haven't evolved to break them down efficiently. The biochemists fed strong 2,4,5-T solutions to mixtures of bacterial strains that have some capacity to break down pesticides. Out of this have come bacteria with the right genetic makeup to thrive on the poison.

Human beings have thoughtlessly poisoned many parts of their environment. Research such as this suggests that microbes, which already clean up much of Earth's waste, may be help us with the chemical waste problem, too.

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