Dust as a nutrient source to the N2-fixing marine cyanobacterium Trichodesmium.

– Yeala Shaked, Hebrew University & Interuniversity Institute for Marine Sciences, Israel –

Résumé :

Desert dust is an important source of the macro and micro nutrients to remote ocean regions, but its utilization by phytoplankton is constrained by its rapid sinking and low mineral solubility. Today, I’ll present several interdisciplinary studies showing that natural colonies of the globally important cyanobacterium Trichodesmium Spp. overcome these constrains by efficient dust capturing and active dust dissolution.

Studying natural Trichodesmium colonies from the Northern Red Sea, we discovered several unique adaptive mechanisms for capturing and storing dust particles within the colony core that enable efficient utilization of iron (Fe) from dust [1-9]. We showed that dust packaging within the colony core is beneficial for uptake, since cell-particle proximity minimize iron loss by diffusion [4,7]. We found that Trichodesmium can selectively collect and retain Fe-rich dust particles, thus optimizing Fe supply [6]. We discovered that Trichodesmium and its associated bacteria act together to increase availability of dust-bound iron, where bacteria secrete Fe-binding molecules that promote dust dissolution and Trichodesmium provides dust and optimal physical settings for dissolution and uptake [2-5]. Over the last years we expanded our research to phosphorus [9] and added new disciplines and techniques such as molecular biology, organic chemistry, high resolution imaging and micro-electrodes. I will show selected findings from these ongoing studies.

 Trichodesmium is predicted to flourish in the warmer, more acidic and “dustier” future ocean. The mechanistic understanding gained by our research on its ability to utilize dust as a nutrient source will enhance our capacity for predicting the ocean’s operation modes in face of global change, and hence its impact on the atmosphere and climate.