Polyphosphate: The "Dark Matter" of Bacterial Chromatin Structure

Polyphosphate (polyP), broadly defined, consists of a chain of orthophosphate units connected by phosphoanhydride bonds. PolyP is the only universal inorganic biopolymer known to date and is present in all three domains of life. At a first approximation polyP appears to be a simple, featureless, and flexible polyanion. A growing body of evidence suggests that polyP is not as featureless as originally thought: it can form a wide variety of complexes and condensates through association with proteins, nucleic acids, and inorganic ions. It is becoming apparent that the emergent properties of the condensate superstructures it forms are both complex and dynamic. Importantly, growing evidence suggests that polyP can affect bacterial chromatin, both directly and by mediating interactions between DNA and proteins. In an increasing number of contexts, it is becoming apparent that polyP profoundly impacts both chromosomal structure and gene regulation in bacteria, thus serving as a rarely considered, but highly important, component in bacterial nucleoid biology.