Dynamic Polyphosphate Metabolism Coordinating with Manganese Ions Defends against Oxidative Stress in the Extreme Bacterium Deinococcus radiodurans.

ABSTRACT

Deinococcus radiodurans is an extreme bacterium with unparalleled resistance to oxidative stresses. Accumulation of intracellular Mn2+ complexing with small metabolites is the key contributor to the tolerance of D. radiodurans against oxidative stress. However, the intracellular reservoir of Mn ions and homeostatic regulation of the Mn complex in D. radiodurans remain unclear. We identified an evolutionarily ancient and negatively charged phosphate polymer (polyphosphate [PolyP]) in D. radiodurans We investigated PolyP metabolism in the response of D. radiodurans to oxidative stress. The genes dr1939, encoding polyphosphatase kinase (PPKDr; the subscript "Dr" refers to D. radiodurans), and dra0185, encoding exopolyphosphatase (PPXDr), were identified. PPXDr is a novel exopolyphosphatase with a cofactor preference to Mn2+, which enhances the dimerization and activity of PPXDr to allow the effective cleavage of PolyP-Mn. PPKDr and PPXDr exhibited different dynamic expression profiles under oxidative stress. First, ppkDr was upregulated leading to the accumulation of PolyP, which chelated large amounts of intracellular Mn ions. Subsequently, the expression level of ppkDr decreased while ppxDr was substantially upregulated and effectively hydrolyzed inactive PolyP-Mn to release phosphate (Pi) and Mn2+, which could form into Mn-Pi complexes to scavenge O2- and protect proteins from oxidative damage. Hence, dynamic cellular PolyP metabolites complexed with free Mn ions highlight a defense strategy of D. radiodurans in response to oxidative stress.IMPORTANCE The Mn-phosphate complex (Mn-Pi) plays a key role in the cellular resistance of radioresistant bacteria. The evolutionarily ancient polyphosphate polymers (polyphosphate [PolyP]) could effectively chelate Mn2+ and donate phosphates. However, the intracellular reservoir of Mn ions and homeostatic regulation of the Mn-Pi complex remain unclear. Here, we investigated the relationship of PolyP metabolites and Mn2+ homeostasis and how they function to defend against oxidative stress in the radioresistant bacterium Deinococcus radiodurans We found that PPXDr (the subscript "Dr" refers to D. radiodurans) is a novel exopolyphosphatase with a cofactor preference for Mn2+, mediating PolyP-Mn degradation into Pi and Mn ions. The formed Mn-Pi complexes effectively protect proteins. The dynamic PolyP metabolism coordinating with Mn ions is a defense strategy of D. radiodurans in response to oxidative stress. The findings not only provide new insights into the resistance mechanism of the extreme bacterium D. radiodurans but also broaden our understanding of the functions of PolyP metabolism in organisms.