Phosphorus is an essential nutrient for life. The release ofphosphorus from sediments is critical in sustaining phytoplankton growthin many aquatic systems and is pivotal to eutrophication and thedevelopment of bottom water hypoxia. Conventionally, sedimentphosphorus release is thought to be controlled by changes in iron oxidereduction driven by variations in external environmental factors, such asorganic matter input and bottom water oxygen. Here, we show thatinternal shifts in microbial communities, and specifically the populationdynamics of cable bacteria, can also induce strong seasonality insedimentary iron-phosphorus dynamics. Field observations in a seasonallyhypoxic coastal basin demonstrate that the long-range electrogenicmetabolism of cable bacteria leads to a dissolution of iron sulfides inwinter and spring. Subsequent oxidation of the mobilized ferrous iron withmanganese oxides results in a large stock of iron-oxide-bound phosphorusbelow the oxic zone. In summer, when bottom water hypoxia develops and cable bacteria are undetectable, the phosphorusassociated with these iron oxides is released, strongly increasing phosphorus availability in the water column. Future researchshould elucidate whether formation of iron-oxide-bound phosphorus driven by cable bacteria, as observed in this study,contributes to the seasonality in iron-phosphorus cycling in aquatic sediments worldwide.
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