Lifestyles of the Small and Obscure

Natural History, June, 2001 by Ellen Goldensohn

Science, a product of the human mind, has delivered repeated blows to the human ego. Copernicus removed us from the center of the solar system. Darwin displaced us from near-angelic status by sticking us on a quite ordinary, though relatively new and green, branch of the animal family tree. Edwin Hubble informed us that the Milky Way is an undistinguished galaxy in a nondescript corner of the universe. Then came the Human Genome Project. When a draft of our genome was published in February of this year, we learned that we don't even have as many genes as we thought we did. The estimated 100,000 was pared down to a mere 33,000--not all that much bigger than the genome of a mouse (28,000), a fruit fly (23,000), or a nematode (22,000). Of course, numbers aren't everything, but these findings do bruise our vanity.

So far, gene-sequencing professionals have devoted most of their attention to bacteria, whose genomes typically have between 1,500 and 4,000 genes. And as the most abundant (and arguably the most influential) organisms on Earth, bacteria deserve the limelight. About 2 billion years ago, they made complex life possible by getting themselves incorporated into larger cells and going on to do the jobs of respiration and photosynthesis in animals and plants. (Plants and animals, including humans, still carry bacterial descendants in each cell, as Lynn Margulis and Dorion Sagan explain in "The Beast With Five Genomes," page 38.)

Genomic studies can tell us something about how bacteria behave in human bodies and other habitats. Turn to "Bacterial Revelations" (page 52) for new insights into the obscure lifestyles of several germs--including the tuberculosis bacillus, the typhus pathogen, and the sea-dwelling Prochlorococcus marinus, the world's smallest and most common photosynthetic bacterium.