Utilization of organic nutrients by coccolithophores

Coccolithophores play a prominent role in the marine, and by extension the global, car- bon cycle. The ability of coccolithophores to thrive on organic nutrients is assumed to be a key rea- son for their ecological success, as Emiliania huxleyi grows well on a variety of organic nutrients. The ability of other coccolithophores to utilize organic nutrients has, however, not been investigated. We conducted experiments to compare the ability of E. huxleyi, Coccolithus braarudii, and Calcidiscus leptoporus to grow on environmentally common organic nitrogen and phosphorus sources (glycine, L-alanine, L-proline, L-serine, L-glutanic acid, L-histidine, urea, glycerophosphate, adenosine monophosphate, adenosine triphosphate, and β-nicotinamide adenine dinucleotide). The nitrogen and phosphorus additions (200 µM and 14 µM, respectively) were higher than naturally occurring in the ocean, as our goal was to test the ability of coccolithophores to utilize these substances. E. huxleyi was able to grow on all tested organic nutrients. C. braarudii grew on 7 out of the 10 tested nutrient sources, but did not grow on 3 amino acids. C. leptoporus grew on only 3 out of the 7 tested N- sources, with no growth on the 4 amino acids. Similarities in the coccolithophores' ability to utilize specific organic sources suggest common transport systems and enzymes, whereas differences emphasize the presence of species-specific nutrient uptake mechanisms. Such species-specific differ- ences in the ability to utilize certain nutrients may provide explanations for biogeographic distri- bution patterns and substantiate the suspicion that E. huxleyi may not be a good representative of coccolithophores, e.g. for Earth system models.