Fe Fi Fo Fum iron sensing in Trichodesmium?

Trichodesmium is integral to the global microbiome and carbon sequestration which makes it increasingly relevant to study. They use Nitrogenase to fix N₂ but this has high iron (Fe) requirements which in the open ocen is often in low supply.

Researchers tested wild Trichodesmium reaction to natural, Fe-coated and Fe-less dust. Trichodesmium showed a higher short-term interaction, cantering and long-term interaction of natural and Fe-coated dust. They also did a ⁵⁷Fe tracer experiment using submicron scale surface imaging with NanoSIMS and found ⁵⁷Fe in the colony core.

I agree with the researchers that this study provides evidence for the selective collection of dust and Fe-rich particles and the disposal of Fe-free particles. To say this proves Fe sensing I think is an overstep. Trichodesmium interacted more with natural dust which to me suggests a more indiscriminate sensing mechanism, that may be related to particle charge. Also, the retention of the dust could relate to time taken to incorporate particles as Fe-free would have less to incorporate. The researchers may have considered these factors making them irrelevant but the mechanism could be more complicated so future research could provide further insight.  

Kessler, N., Armoza-Zvuloni, R., Wang, S., Basu, S., Weber, P. K., Stuart, R. K., & Shaked, Y. (2019). Selective collection of iron-rich dust particles by natural Trichodesmium colonies. The ISME journal, 1-13.