Jointed threads: Joseph Leidy was the first to describe symbiotic bacteria growing together in long strings in animal intestines. Microbiological analyses now link the bacteria with anthrax

Natural History, June, 2005 by Lynn Margulis

Leidy's meticulous observation of live organisms, Kirby's equally keen empiricism, and our comparative work have made it clear that Bacillus anthracis, the anthrax culprit, comes from a long line of symbionts in animal intestines. Those symbionts are filaments that live inside people, sheep, and various members of barnyard and wild animal communities.

Without its two extra plasmids, the bacterium is harmless. It grows on mushy food both inside and outside the intestine. And when conditions deteriorate, it forms remarkably tolerant propagules--tough, even boilproof, shiny, spores by the millions that waft on air. If we are to be afraid of anthrax, as indeed we must be, we need to condemn those who would deliberately culture a bacillus that is armed with the dangerous plasmids that enable it to be a pathogen, a freak of nature, rather than a law-abiding citizen of the intestinal microcosm.