SUCK UP: Bacterial symbionts living in tropical sponges, like this giant barrel sponge, produce polyphosphate granules. IMAGE COURTESY OF ANDIA CHAVES-FONNEGRA

EDITOR'S CHOICE IN MARINE BIOLOGY

The paper
F. Zhang et al., “Phosphorus sequestration in the form of polyphosphate by microbial symbionts in marine sponges,” PNAS, 112:4381-86, 2015.

Dyed surprise
Fan Zhang, a graduate student in Russell Hill’s lab at the University of Maryland Center for Environmental Science, was using microscopy to study how Caribbean coral reef sponges process nitrogen. But the sponges autofluoresced so brightly that their nitrogen-fixing bacterial symbionts were difficult to see. To detect the bacteria, Zhang applied a blue fluorescent stain called DAPI, but to his surprise, he saw something else: bright yellow dots.

Bacterial origins
An Internet search suggested that polyphosphate—chains of phosphate molecules—could be the cause, and indeed, with specific extraction methods and scanning electron microscopy, Zhang’s team observed polyphosphate granules that accounted...

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