Thiamine (vitamin B1) is a cofactor required for essential biochemical reactions in all living organisms, yet free thiamine is scarce in the environment. Thiamin was present at the earliest stages of the evolution of life, therefore its long history as an essential organic cofactor underlies the potential for strong selection to evolve numerous ecological outcomes associated with its acquisition and use. The diversity of biochemical pathways involved in the acquisition, degradation and synthesis of thiamine indicates that organisms have evolved numerous ecological strategies for meeting this nutritional requirement. We synthesize information from multiple disciplines to show how the complex biochemistry of thiamine influences ecological outcomes of interactions between organisms in environments ranging from the open ocean and the Australian outback to the gastrointestinal tract of animals. We highlight population and ecosystem responses to the availability or absence of thiamine. These include widespread mortality of fishes, birds, and mammals, as well as the thiamine-dependent regulation of primary productivity. Overall, we ask whether thiamine biochemistry is the foundation for molecularly mediated ecological interactions that influence survival and abundance of a vast array of organisms.
The importance of the ecological important of thiamin will be illustrated by reporting results from three lines of investigation that have confirmed our expectation that competition for thiamin influences ecological outcomes in a diverse range of organisms. First, laboratory experiments with cultures of Burkholderia thailandensis and Paenibacillus sp. have demonstrated that these bacteria degrade and synthesize thiamin in a manner that provides these organisms with a competitive advantage over other bacteria in environments with variable levels of thiamin and thiamin precursors. Second, laboratory experiments with Drosophila melanogaster have shown that several strains of bacteria with a thiamin-degrading enzyme (thiaminase I) are pathogenic to Drosophila, but congeners without the thiaminase I enzyme are not pathogenic. Third, our field experiments in streams have demonstrated that thiamin additions can enhance primary production relative to additions of other conventional nutrients (nitrogen as NH4Cl and phosphorus as NaH2PO4); this result was observed in eight of nine experiments conducted in Adirondack (New York, USA) streams from August through October in 2015 and 2016. Overall, our lab and field experiments have consistently demonstrated the importance of thiamin in previously unrecognized ecological contexts.