Polyphosphate dynamics in cyanobacteria and its role in P apatite formation at the sediment water in

Session: Nutrient Sources, Transport, and Internal Cycling (2)

Diane Plouchart, University of Toronto, diane.plouchart@utoronto.ca
Maria Dittrich, University of Toronto Scarborough, mdittrich@utsc.utoronto.ca
Audrey Manuel, University of Toronto Scarborough, audrey.manuel@mail.utoronto.ca
Md Samrat Alam, University of Toronto, samrat.alam@utoronto.ca
David Depew, Environment and Climate Change Canada, David.Depew@canada.ca

Abstract

At high phosphate concentrations, many organisms like the primary producer picocyanobacteria, form intracellular granules of polyphosphates (polyP). These organisms can degrade polyP under phosphate starvation. The dynamics of polyP as a function of available nutrients and its effects at the sediment-water interface remains unclear. The presence of polyP at this interface may lead to the formation of phosphate minerals such as apatite. While investigated in marine sediments, these mechanisms have not been studied in freshwater lakes. We hypothesized that picocyanobacteria containing polyP catalyzed the biomineralization of apatite. Their hydrolysis and release in sediment pore waters would increase apatite supersaturation state until its precipitation.

To assess the potential importance of polyP on the mechanisms underpinning the formation of sedimentary apatite, we first isolated picocyanobacteria cultures from lake water at various locations and depths in Lake Ontario. PolyP concentrations over their growth phases in batch and in continuous cultures were assessed and used for apatite biomineralization experiments performed in anoxic conditions. Preliminary results with polyP extracted from Synechococcus sp. PCC6312 showed calcium-phosphate formations, potentially hydroxyapatite. These results shed light on the presence of microbial polyP in lakes and on their importance regarding sedimentary apatite, an important phosphorus sink in lakes.