The Code Breaker

by Walter Isaacson

What Mojica had stumbled upon was a battlefront in the longest-running, most massive and vicious war on this planet: that between bacteria and the viruses, known as “bacteriophages” or “phages,” that attack them. Phages are the largest category of virus in nature. Indeed, phage viruses are by far the most plentiful biological entity on earth. There are 1031 of them—a trillion phages for every grain of sand, and more than all organisms (including bacteria) combined. In one milliliter (0.03 ounces) of seawater there can be as many as 900 million of these viruses.7 As we humans struggle to fight off novel strains of viruses, it’s useful to note that bacteria have been doing this for about three billion years, give or take a few million centuries. Almost from the beginning of life on this planet, there’s been an intense arms race between bacteria, which developed elaborate methods of defending against viruses, and the ever-evolving viruses, which sought ways to thwart those defenses.