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Abstract:
Iron (Fe) bioavailability limits phytoplankton growth in vast ocean
regions. Iron-rich dust uplifted from deserts is transported in the
atmosphere and deposited on the ocean surface. However, this dust is a
poor source of iron for most phytoplankton since dust-bound Fe is poorly
soluble in seawater and dust rapidly sinks out of the photic zone. An
exception is Trichodesmium, a globally important, N-2 fixing, colony
forming, cyanobacterium, which efficiently captures and shuffles dust to
its colony core. Trichodesmium and bacteria that reside within its
colonies carry out diverse metabolic interactions. Here we show evidence
for mutualistic interactions between Trichodesmium and associated
bacteria for utilization of iron from dust, where bacteria promote dust
dissolution by producing Fe-complexing molecules (siderophores) and
Trichodesmium provides dust and optimal physical settings for
dissolution and uptake. Our results demonstrate how intricate
relationships between producers and consumers can influence productivity
in the nutrient starved open ocean.
