Colonies of the Marine Cyanobacterium Trichodesmium Optimize Dust Utilization by Selective Collection and Retention of Nutrient-Rich Particles

Abstract

Trichodesmium, a globally important, N₂-fixing and colony-forming cyanobacterium employs multiple pathways for acquiring nutrients from air-borne dust, including the active collection of dust particles. Once concentrated within the colony core, dust can supply Trichodesmium with the limiting nutrients iron (Fe) and phosphorus (P). Studying particle collection by natural colonies, we recently documented a preference for Fe-rich over Fe-free particles. In this follow-up study we examined if colonies selectively collect P-rich particles. Over an entire bloom season, we incubated ~1 200 Trichodesmium colonies from the Red Sea with P-free CaCO₃, P-coated CaCO 3 and dust. We utilized three discrete parameters to characterize the colony-particle interactions and integrated them to an index that describes the particle collection behavior over time. Colonies were found to preferably interact, center and retain P-coated CaCO₃ in comparison to P-free CaCO₃, suggesting that Trichodesmium can optimize its P-acquisition by selecting P-rich particles. In both current and former studies, colonies clearly favored dust over all other particles tested, while nutrient-free particles were barely collected or retained, indicating that Trichodesmium senses the particle composition and preferably collects nutrient-rich particles. This unique ability contributes to Trichodesmium's current ecological success and may assist it to flourish in future warmer oceans.