Microcosm: E. coli and the New Science of Life

pedestals, and a network of crisscrossing avenues.

and natural selection rewired its network. One of the simplest means by which E. coli’s network can be rewired is the accidental duplication of a chunk of DNA. In some cases, the duplication may create two copies of the same switch. If the gene for one of those switches mutates, it may begin to control a different gene. In other cases, extra copies

Vertical gene transfer and natural selection act like an in-house team of software developers, hiding the details of their innovations from the community. Horizontal gene transfer allows E. coli to grab chunks of software and test them in its own operating system.

controlled by the switch that turned on the original gene.

When scientists map the pathways that a carbon atom can take through E. coli’s metabolism, the picture they see looks like a bow tie. On one side of the bow tie are the chemical reactions that draw in food and break it down. These reactions follow each other along simple pathways, a fan of incoming arrows. Eventually the arrows all converge on the

Bernhard Palsson, a biologist at the University of California, San Diego, has overseen the construction of a model of E. coli’s metabolism.

We share with E. coli a basic genetic code and many proteins essential for getting energy from food. E. coli and our own cells face many of the same challenges. They both need to keep a boundary with the outside world intact yet not too rigid. E. coli has to keep its DNA neatly folded and yet accessible for speed-reading. It has to keep track of it

Between the outer and inner membranes of E. coli is a thin cushion of fluid, called the periplasm. The periplasm is loaded with enzymes that can disable dangerous molecules before they are able to pass through the inner membrane.

In fact, E. coli makes just the right number of heat-shock proteins to cope with a particular temperature. It makes more proteins for higher temperatures, fewer for cooler ones.