Polyphosphate-accumulating microorganisms in aquatic sediments

The direct contribution of microorganisms to the mobilisation and immobilisation of phosphorus (P) in aquatic sediments has been controversially discussed for more than a decade. Some authors have speculated that the microbial P pool is highly variable in the uppermost sediment layer, especially when excessive P accumulation in the form of polyphosphate (Poly-P) occurs. Poly-P storage is a widespread ability of many different organisms in nature. The phenomenon of Poly-P storage has been technically optimised in wastewater treatment plants (WWTP) providing conditions for enhanced biological phosphorus removal. New insights into the functioning of P elimination in WWTP were strongly linked to the development of novel methods, like P-31 nuclear magnetic resonance, for the detection of Poly-P and molecular biological methods for the identification of the specific microorganisms responsible for biological P elimination. Our review summarises current literature on Poly-P in aquatic systems and discusses different potential habitats and mechanisms for Poly-P storage in sediments that are more diverse than in WWTP. Poly-P in sediments may originate from benthic or pelagic hetero- and autotrophic organisms. Poly-P-accumulating organisms in sediments may be of high ecological importance, since they insert phosphorus into the benthic food chain and affect the permanent P mineral deposition in sediments by physiologically inducing rapid P release. Although several studies indicate that Poly-P substantially contributes to total P in the uppermost sediment layer (up to 10%), its origin and the microorganisms and mechanisms involved in Poly-P storage and cycling are largely unknown. Therefore, we also aim to stimulate future studies focusing on these irnportant areas of sediment research.