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Institut de minéralogie, de physique des matériaux et de cosmochimie
UMR 7590 - Sorbonne Université/CNRS/MNHN/IRD


Phosphorus (P) is central to the functioning of ecosystems as well as many strategies aiming at a sustainable management of environmental resources. In order to increase the sustainability of P-resources managements, it is crucial to significantly improve our knowledge about the detailed processes, fluxes and reservoirs involved in the geochemical cycle of P. 

Microorganisms have been shown to be major actors in modern and past geochemical cycles of P either as reservoirs and/or catalysts of processes exchanging P between different reservoirs. Only few microbial models involved in the intracellular sequestration of P have been described, mainly isolated in oxic-anoxic transition zones at the water-sediment interface. Recently, we identified freshwater magnetotactic bacteria (MTB) affiliated to the Magnetococcaceae family, which accumulate intracellular polyphosphates (PolyP) to a uniquely high extent (>90% of their cell volume and 10 to 30 times more than other microbes in the same environment; Rivas-Lamelo et al. 2017, Geochem. Persp. Lett.). We detected them at the oxic-anoxic interface within the water column of Lake Pavin (Massif Central), a poorly sulfidic environment.

The PHOSTORE project, with an inherent questioning about the interactions between living systems and solid inorganic phases, will test 4 main hypotheses: (1) Magnetococcaceae are an important reservoir of P in Lake Pavin by its size (compared to other microbes) and/or its turnover rate, i.e. the in-flux or out-flux from this microbial reservoir to the dissolved inorganic P reservoir. The release of P by MTB can take place in the water column and/or in the sediment following cell sedimentation; (2) Magnetococcaceae accumulate PolyP to the same extent as bacteria known as P-hyperaccumulators, with a higher efficiency compared to other known MTB models; (3) Chemical variations such as those encountered in the water column of Lake Pavin impact the storage/hydrolysis balance of PolyP by Magnetococcaceae; (4) Magnetococcaceae genomes harbor a specific repertoire of genes involved in the metabolism of P. This repertoire can be particularly rich and/or diverse, in regulatory networks related to the above-mentioned environmental parameters, or highly expressed. 

Overall, we propose the first exploration of the diversity of MTB in a ferruginous freshwater environment and their impact on the P cycle in a context of phosphatogenesis. We will characterize new microbial models for efficient P sequestration and provide fundamental knowledge on the key relationships between microbial diversity, environmental parameters and P cycling. We will identify key physicochemical parameters favoring storage of P by MTB. In the longer term, this may feed applications such as the development of bioremediation strategies.


Fig. Caption: STEM and EDXS analyses of PolyP and S-granules in MTB cells. Left: STEM image in HAADF mode and overlay of Fe (green), P (blue) and S (red) in two different areas. Right: EDXS spectra of S-granules (orange) and PolyP inclusions (blue).

Rivas-Lamelo et al. 2017, Geochem. Persp. Lett.

Cécile Duflot - 24/11/20

Traductions :

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