The Glacier Ice Worm, Mesenchytraeus solifugus , Elevates Mitochondrial Inorganic Polyphosphate (PolyP) Levels in Response to Stress.

The inorganic polymer, polyphosphate (polyP), is present in all organisms examined to date with putative functions ranging from the maintenance of bioenergetics to stress resilience and protein homeostasis. Bioenergetics in the glacier-obligate, segmented worm, , is characterized by a paradoxical increase in intracellular ATP levels as temperatures decline. We show here that steady-state, mitochondrial polyP levels vary among species of Annelida, but were elevated only in in response to thermal stress. In contrast, polyP levels decreased with temperature in the mesophilic worm, . These results identify fundamentally different bioenergetic strategies between closely related annelid worms, and suggest that I worm mitochondria maintain ATP and polyP in a dynamic equilibrium.