Bacterial diet quiets worm genes. (Genetics).

It's a gene-loss, not weight-loss, diet. By feeding genetically engineered bacteria to worms, researchers have developed an easy way to deactivate specific worm genes and study their function.

Biologists frequently choose the tiny worm Caenorhabditis elegans for their studies, in part because they've already identified most, if not all, of the worm's genes (SN: 12/12/98, p. 372). To study a gene's roles, many investigators have turned to a method called RNA interference. By injecting a worm with a strand of RNA corresponding to the gene's DNA sequence, scientists can turn off that particular gene and observe what happens to the animal (SN: 1/15/00, p. 36).

Injecting worms with lab-made RNA molecules, one-by-one, for each of the animal's 19,000 or so genes would be tedious work. Andrew Fraser of the University of Cambridge in England and his colleagues came up with another plan. The researchers have so far created nearly 17,000 strains of the bacterium Escherichia coli, each one genetically engineered to make a different piece of RNA. When a worm dines on one of these microbial strains, the microbe's RNA is freed to turn off the corresponding worm gene.

Fraser's group has found that in 1 in 10 cases, the silencing of a gene by this method produces obvious abnormalities. For about 1,100 of the silenced genes, the growing worm dies. For others, the worms are sterile, move around in an unusual manner or don't mature normally.

Fraser and his colleagues plan to make their bacterial library available to other scientists. Fraser says that his team will also finish creating its set of RNA-making E. coli. "We want to analyze all the genes in the genome," he says.