As E. coli runs out of its essential nutrients, its ribosomes get sloppy, producing misshapen protein that attacks other molecules. The catastrophe can ripple out across the entire microbe. To continue to grow under such stress would be suicidal, like driving a car over a cliff. Instead, E. coli slams on the brakes. In a matter of seconds it stops

That’s a lot of time and energy for a microbe to invest. The investment may pay off or it may be a waste of effort—the lactose may disappear quickly or a more energy-rich sugar may turn up.

But E. coli has to pay a price for this weaponry. It has to use energy to make colicins and antidotes, which are particularly big as bacterial molecules go. A new colicin may be even deadlier than its predecessor, but it may also become a drain on a microbe.

operon meaning a set of genes that are all regulated by the same switches.

E. coli builds chemical weapons. Known as colicins, these deadly molecules kill in many ways. Some pierce the microbe’s membrane like a spear, forcing its innards to spill out. Others block E. coli from building new proteins. Others destroy DNA.

when the temperature is cool, E. coli is constantly reading the gene for sigma 32 and making RNA copies. But at normal temperatures the RNA folds in on itself, and so E. coli cannot use it to make a protein. At normal temperatures the microbe is loaded with sigma 32 RNA but no actual sigma 32 protein.

Enzymes are actually not all that finely tuned. An enzyme that can slice up one molecule very efficiently may slice up other kinds of molecules, too, albeit more slowly and clumsily.

If you want to add a toggle switch to your particular circuit, you can search for it on the BioBricks Web site, download the DNA sequence, order the corresponding fragments of DNA from a biotech firm, and insert them in E. coli.

It grows looming towers, broad