Microcosm_ E. Coli and the New Science of Life - Carl Zimmer [102]
While we’ve been waiting for a genetically engineered monster to emerge, E. coli O157:H7 has emerged as a serious threat to public health. It was in 1975—the same year in which scientists gathered at Asilomar to ponder the potential dangers of genetically engineered E. coli—that a woman suffered the earliest known attack of E. coli O157:H7. But that pathogen was not the work of a human genetic engineer with an intelligent design. Over the course of centuries, E. coli O157:H7 acquired many genes from viruses carrying deadly instructions. They acquired these genes from other strains of E. coli or other species of bacteria. They acquired syringes and toxins and molecules that alter the behavior of host cells. This genetic engineering is still taking place as one new strain after another evolves. But the insertion of a bundle of genes in a single microbe was only the first step in this transformation. Natural selection then had to favor those genes in their new host; it had to fine-tune them.
The transformation required an entire ecosystem that could produce the conditions that would drive natural selection. We provided it. E. coli O157:H7 had been pumped from humans to livestock through farm fields and slaughterhouses, through rivers and sewers rife with toxin-bearing viruses. There’s little evidence for a similar evolutionary pump for genetically engineered E. coli. Our unplanned engineering of E. coli may give us more to worry about than anything brewed up in a lab.
Thirty years have passed since the backers of genetic engineering predicted recombinant DNA would bring great rewards. They were right, up to a point. E. coli and other engineered cells not only produce a vast number of valuable molecules; they have also sped up the pace of science enormously. E. coli was a crucial partner in the sequencing of the human genome, for example. In order to read the genome, scientists inserted chunks of it into E. coli, which then produced many copies that scientists could analyze. Other scientists have used E. coli to churn out millions of proteins so that they can discover what the proteins do. By inserting human genes into E. coli, scientists discovered that they are made up of two kinds of DNA. Some segments of the genes, known as exons, encode parts of proteins. But they alternate with other segments, called introns, that encode nothing. Our cells edit out the introns from RNA in order to make proteins. They can even use different combinations of exons to produce a number of proteins from a single gene.
As important as these accomplishments have been, however, genetic engineering has fallen far short of the more extravagant promises offered thirty years ago. Cetus predicted that all major diseases would surrender to genetically engineered proteins by 2000. I’m writing in 2007, and cancer, heart disease, malaria, and other diseases continue to kill by the millions. Maybe the people at Cetus were just wrong about the date. Perhaps another thirty years will bring some major breakthrough in genetic engineering that will wipe out all major diseases. I wouldn’t bet on it, though. Most major diseases are fiendishly complex, and a single engineered protein is not going to make them go away. Diabetes, the poster child for the promise of genetic engineering, has not disappeared over the past thirty years. In fact, it has exploded. The incidence of type 2 diabetes has doubled in the United States, and cases of diabetes worldwide have increased tenfold. E. coli has provided insulin for millions of people with diabetes, but, as Ruth Hubbard warned, it did nothing to prevent the disease. Genetic engineering could not block the sources of the diabetes epidemic, which may include the availability of cheap sugar. That sugar comes increasingly from high-fructose corn syrup, whose low price we owe to breakthroughs in genetic engineering.