Widespread decay of vitamin-related pathways: coincidence or consequence?

• We examine evidence for vitamin-associated pathway loss across eukaryotes.
• This process can explain the differentiation of vitamin auxotrophy among species.
• Commonalities in vitamin metabolism influence the evolution of vitamin auxotrophy.
• Vitamins have been important in shaping biotic interactions throughout evolution.

The advent of modern genomics has provided an unparalleled opportunity to consider the gene complement of an organism, and scrutinize metabolic pathways that are no longer active. This approach has led to an increasing number of reports of vitamin-associated pathway deterioration, with many indicating that independent gene-loss events of one or a few key genes have led to vitamin auxotrophy. Nonfunctional unitary pseudogenes belonging to these pathways are found in several species, demonstrating that these are recent evolutionary processes. Here, we examine the commonalities in the cellular roles and metabolism of vitamins that might have led to these losses. The complex pattern of vitamin auxotrophy across the eukaryotic tree of life is intimately connected with the interdependence between organisms. The importance of this process in terms of shaping communities on the one hand, and facilitating symbioses between organisms on the other, is only just beginning to be recognized.