Sponge Symbionts Sequester Phosphorus

Coral reefs have mystified scientists for decades. Reefs support dazzlingly diverse ecosystems even though the water surrounding them appears to lack phosphorus, an element essential to life. A team of researchers led by Russell T. Hill of the University of Maryland has now shown that bacteria living in sponges could be sopping up substantial amounts of phosphorus and delivering it to the food chain as polyphosphate (Proc. Natl. Acad. Sci. USA 2015, DOI: 10.1073/pnas.1423768112). While looking for nitrogen-fixing bacteria under a microscope, the team inadvertently discovered that three species of sponges from the Conch Reef, in the Florida Keys, harbored polyphosphate granules. Fan Zhang, a graduate student on the team, stained the bacteria with a dye that binds to DNA and normally fluoresces blue light. Zhang instead observed a yellow glow, which the dye can emit when bound to polyphosphate. The team confirmed the compound was responsible for the yellow shift by using energy-dispersive X-ray spectroscopy. The team also found polyphosphate within microbial sponge symbionts and in bacteria cultured from sponge tissue, indicating the crystals are microbial in origin.