Polyphosphate

Polyphosphate, commonly abbreviated polyP, is a linear polymer composed of many inorganic phosphate (Pi) units joined by phosphoanhydride bonds. The repeating unit is a phosphate residue linked to its neighbor by a high-energy P–O–P bond, giving a highly negatively charged chain. Depending on conditions and organisms, polyP chains can range from a few to hundreds of phosphate units.

PolyP occurs in all domains of life. In bacteria, it serves as a phosphate and energy reserve and participates in stress response, virulence, and biofilm formation. In eukaryotes, polyP is found in organelles such as mitochondria and chloroplasts and may play roles in energy metabolism and signaling. In many microbes, polyP is stored in acidocalcisomes, vacuoles rich in calcium and polyP.

Biosynthesis and degradation: PolyP is synthesized by polyphosphate kinases (PPK1, PPK2) using ATP or other nucleoside triphosphates as phosphate donors. It is degraded by exopolyphosphatases (PPX) and endopolyphosphatases, releasing inorganic phosphate. The chain length and turnover are tightly regulated by cellular phosphate status and stress conditions.

Functions and properties: polyP is highly anionic and binds metal cations such as Mg2+ and Ca2+, contributing to metal homeostasis and buffering. It acts as a phosphate and energy reserve, supports stress adaptation, and modulates enzyme activity and signaling in some organisms. In environmental microbiology, polyP accumulation by bacteria under anaerobic conditions is central to enhanced biological phosphorus removal (EBPR) processes.

Applications and notes: In industry, polyP is used as a sequestrant and thickener and is listed as food additive E450. Biotechnological interest focuses on manipulating polyP metabolism for wastewater treatment, biotechnology, and health-related functions. The chemistry and biology of polyP continue to be studied for its simple structure and wide-ranging biological roles.