Dependency can be an evolutionary advantage
It has been known for quite some time that genetically modified bacteria, which have lost their ability to produce certain amino acids and retrieve these nutrients from their environment grow better than bacteria, which produce all nutrients themselves (see press release Division of Labor in the Test Tube, December 2, 2013). This led Christian Kost, leader of the study and now professor at the University of Osnabrück, to inquire whether natural selection would favor the loss of abilities, thus making bacteria more dependent on their environment. To find out, Kost and his PhD student Glen D'Souza cultivated the gut bacterium Escherichia coli bacteria for several generations under optimal nutritious conditions. The culture was regularly transferred to a fresh nutrient solution, and during some of these transfers, a sample was taken to examine the bacterial capabilities and genes.