““For example, all three partners cooperate to make nutrients. To create the amino acid phenylalanine, they need nine enzymes. Tremblaya can build 1,2,5,6,7, and 8; Moranella can make 3,4, and 5; and the mealybug alone makes the 9th. Neither mealybug nor the two bacteria can make phenylalanine on their own; they depend on each other to fill the gaps in their repertoires. This reminds me of the Graeae of Greek mythology: the three sisters who share one ee and one tooth between them. Anything more would be redundant: their arrangement, though odd, still allows them to see and chew. So it is with the mealybug and its symbionts. They ended up with a single metabolic network, distributed between their three complementary genomes. In the arithmetic of symbionts, one plus one plus one can equal one.””
