Phosphorus (P) is a vital nutrient required by all forms of life. Marine microorganisms utilize P hydrolases, such as alkaline phosphatase (AP) and C-P lyase, to acquire phosphate (Pi) from a wide diversity of P-containing compounds in seawater, which together comprise the pool of dissolved organic P (DOP): phosphonates (C-P bonds), polyphosphates (P-O-P), and phosphomono- (P-O-C) and diesters (C-O-P-O-C). The dephosphorylation of specific P-containing compounds exerts critical and wide-ranging impacts on marine microbial ecology, marine productivity, and global climate.
The Duhamel Lab has been studying alkaline phosphatase in a range of marine and freshwater environments. For more information on what we have learned so far, please click here:
Our most recent project about P-hydrolases was funded by the National Science Foundation to work with the group of Dr. Julia Diaz at the Scripps Institution of Oceanography
Collaborative Research: Assessing the role of compound-specific phosphorus hydrolase transformations in the marine phosphorus cycle
ABSTRACT
Phosphorus (P) is a vital nutrient for life. Marine microorganisms utilize P-hydrolases, such as alkaline phosphatase (AP), to release and acquire phosphate (Pi) from a wide diversity of dissolved organic P (DOP) compounds, including P-esters (P-O-C bonds), phosphonates (P-C), and polyphosphates (P-O-P). Compound-specific DOP transformations have the potential to exert critical and wide-ranging impacts on marine microbial ecology (e.g. variable DOP bioavailability among species), biogeochemistry (e.g. P geologic sequestration via formation of calcium Pi), and global climate (e.g. aerobic production of the greenhouse gas methane by dephosphorylation of methylphosphonate). However, the mechanisms and comparative magnitude of specific DOP transformations, in addition to their relative contributions to microbial community-level P demand, productivity, and structure, are not completely understood. This study will fill these knowledge gaps by tracking the fate of specific DOP pools in the marine environment. Specifically, this project will test four hypotheses in the laboratory using recombinant enzymes and axenic cultures representative of marine eukaryotic and prokaryotic plankton from high and low nutrient environments, and in the field using observational and experimental approaches along natural Pi gradients in the Atlantic Ocean. In particular, the investigators will reveal potential differences in the hydrolysis and utilization of specific DOP compounds at the community- (bulk enzymatic assays), taxon- (cell sorting of radiolabeled cells in natural samples), species- (axenic cultures) and molecular-levels (pure enzyme kinetic studies and cell-associated proteomes and exoproteomes). Results from our proposed work will provide a robust understanding of the enzymatic basis involved in the transformation of specific forms of DOP and create new knowledge on the relative contribution of these specific P sources to Pi production, marine microbial nutrition, community structure, primary productivity, and thus global carbon cycling and climate. In particular, our refined measurements of the concentration of bioavailable DOP and our unique estimates of DOP remineralization fluxes will provide critical new information to improve models of marine primary production and P cycling.
The grant has so far resulted in the following publications:
Filella A., Riemann L., Van Wambeke F., Pulido-Villena E., Vogts A., Bonnet S., Grosso O., Diaz J.M., Duhamel S., and M. Benavides. 2022. Contrasting roles of DOP as a source of phosphorus and energy for marine diazotrophs. Frontiers in Marine Science, 9. doi.org/10.3389/fmars.2022.923765
Rabouille, S., Tournier, L., Duhamel, S., Claquin, P., Crispi, O., Talec, A., Landolfi, A., A. Oschlies. 2022. Organic phosphorus scavenging supports efficient growth of diazotrophic cyanobacteria under phosphate depletion. Frontiers in Microbiology, 13. doi.org/10.3389/fmicb.2022.848647
Adams J.C., Steffen R., Chou C-W., Duhamel S., and J.M. Diaz.2022. Dissolved organic phosphorus utilization by the marine bacterium Ruegeria pomeroyi DSS-3 reveals chain length-dependent polyphosphate degradation. Environmental Microbiology, 24: 2259-2269. doi.org/10.1111/1462-2920.15877
Duhamel S., J.M Diaz, J.C. Adams, K. Djaoudi, V. Steck, E.M. Waggoner. 2021. Phosphorus as an integral component of global marine biogeochemistry. Nature Geosciences. 14, 359–368, https://doi.org/10.1038/s41561-021-00755-8
Diaz J.M., Steffen R., Sanders J.G., Tang Y., and S. Duhamel. 2019. Preferential utilization of inorganic polyphosphate over other bioavailable phosphorus sources by the model diatoms Thalassiosira spp. Environmental Microbiology, 21, 2415–2425, doi: 10.1111/1462-2920.14630. Open access
Diaz J.M., Holland A., Sanders J.G., Bulski K., Mollett D., Chou C-W., Phillips D., Tang Y., And S. Duhamel. Dissolved organic phosphorus utilization by phytoplankton reveals preferential degradation of polyphosphates over phosphomonoesters. Frontiers in Marine Sciences, 5, 380, doi: 10.3389/fmars.2018.00380. Open access