Symbiotic Associations: All About Chemistry

Abstract

Biology is a challenging discipline because there is so much to know and so much to learn about the details of how living things work. The lessons that symbiosis has to teach are an excellent place to start, because they are some of the most interesting stories that biology has to tell. Symbioses are not just interesting, they are really important in evolution. Eukaryotes owe their existence to a fateful symbiotic encounter between an archaeal host and a bacterial symbiont, the ancestor of mitochondria, more than 1.5 billion years ago. The origin of the plant kingdom roots in a singular symbiotic association between a eukaryotic host and a cyanobacterium that gave rise to the plastid more than 1.2 billion years ago. In order for endosymbioses to become established, the two partners first need to meet and to stay associated over a protracted period of time so that the endosymbiont can evolve into an organelle. Then, in order for two symbiotic partners to remain associated after their first meeting, there has to be some kind of mechanistic benefit or dependence involved that will keep the one cell located next to-or stably maintained within-the other. In microbial symbioses, benefits are typically paid out in the currency of chemical substances. In this chapter, examples are covered that illustrate that principle.