Electron microscopic analysis of heat-induced leakage of polyphosphate from a phoU mutant of Escherichia coli.

Heat treatment is a simple technique for releasing polyphosphate (polyP) from microbial cells. We investigated the ultrastructural alterations of polyP granules (PPGs) in response to heat treatment at 70 degrees C using a polyP-accumulating phoU mutant of Escherichia coli as a model organism. Electron microscopic and energy-dispersive X-ray analysis suggested concurrent occurrence of PPG degradation and polyP release in the cytoplasm. PolyP is probably released by cytoplasmic extrusion through breaks in the cell envelope.