Queen's University, Belfast, Northern Ireland

A microbiologist learns that all marine creatures must suffer for the greed of a few.

Phosphate is an essential nutrient for all forms of life. Demand for it tends to outstrip supply to such an extent that it limits the overall productivity of many ecosystems, including vast tracts of the seas. I study the curious strategies by which creatures obtain sufficient phosphate for life as they know it.

Some microorganisms, for instance, keep a phosphate store for when times are hard. They scavenge for the nutrient in their surroundings with high-affinity uptake systems and then produce polyphosphate, an insoluble polymer that packs hundreds of phosphate subunits into a single strand. Strands of polyphosphate then form intracellular granules that can be broken down by cellular enzymes when they are needed.

This kind of 'luxury' uptake was recently the focus of a study by Ellery Ingall of the Georgia Institute of Technology in Atlanta and his colleagues. Diatoms — unicellular, silica-walled algae — accumulate phosphate during summer blooms to levels far beyond their immediate needs. Indeed, polyphosphate produced by plankton accounted for 7–11% of the total phosphate in the surface waters of Effingham Inlet, a fjord on Vancouver Island, Canada (J. Diaz et al. Science 320, 652–655; 2008).

This self-indulgent behaviour seems to have far-reaching consequences. Decaying plankton eventually sink to the ocean floor, where they spill unused polyphosphate onto the sediment surface. Notably, Ingall and his team found that soluble phosphate was not released at this point. Instead, polyphosphate molecules seeded the precipitation of minerals called apatites, a process that took only a few years. So diatom greed may ultimately lower the ceiling on marine productivity by locking away the oceans' most hard-to-come-by nutrient. That is important as well as curious.