Dead Bacteria Walking

By all accounts, they shouldn't exist. But two bacteria are beating the odds, living despite the absence of genes considered to be essential for life.

In last week's issue of Science, researchers reported the completion of two genome sequences for two bacterial organisms that have mutually beneficial relationships with their insect hosts. (The bacteria are known as endosymbionts, because they live inside their hosts' cells.) The genomes of both bacteria—Carsonella ruddii and Buchnera aphidicola—are smaller than researchers previously believed possible.