לוח שנה משולב

Diatoms are among the most globally distributed and ecologically successful organisms in the modern ocean, contributing upwards of 40% of total marine primary productivity. Diatom production is tightly coupled with carbon export through the ballasted nature of the silica-based cell wall, linking the oceanic silicon and carbon cycles. While viruses are considered key players in ocean biogeochemical cycles, little is known about how viral infection specifically impacts diatom populations. Using a suite of molecular, physiological and geochemical approaches, we explored diatoms and associated viruses across diverse nutrient regimes in the northeast Pacific. We found that silicon (Si) limitation facilitated virus infection and mortality in diatoms while the onset of iron (Fe) limitation, in sharp contrast, substantially reduced viral replication. These findings, recapitulated in model systems, suggest that virus-mediated mortality in Si-limited regimes would facilitate diatom remineralization in the surface ocean, while diatoms in Fe-limited regimes may escape viral lysis, ultimately contributing to carbon export. We also explored how viral infection of diatoms might impact the microbial processing of organic matter in the ocean. Using bacterial isolates and model diatom host-virus systems, we tested how bacteria respond to dissolved organic matter generated during viral infection in diatoms. We found that this material can significantly stimulate ectoproteolytic activity, implicating viral infection of diatoms in bacteria-mediated recycling of organic matter and silica in the surface ocean. Together, these findings highlight the dynamic role that diatom host–virus interactions play in shaping the biogeochemical landscape the global ocean.

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Crystallization plays an important role in many areas of biology, chemistry and materials science, but the underlying mechanisms that govern crystallization are still poorly understood because of experimental limitations in the analysis of such complex, evolving systems. To derive a fundamental understanding of crystallization processes, it is essential to access the sequence of solid phases produced as a function of time, with atomic-level resolution. Rationalization of crystallization processes is particularly relevant for polymorphic materials, i.e. solids that can exist as distinct crystalline forms. Indeed, polymorphism can have huge economic and practical consequences for industrial applications in pharmacy and energy because different polymorphs display different physicochemical properties. If, on the one hand, it offers great opportunities for tuning the performance of the material, on the other hand, manufacture or storage-induced, unexpected, polymorph transitions can compromise the end-use of the solid product. Interestingly, these transformations often imply the formation of metastable forms, which are receiving growing attention because they can offer new crystal forms with improved properties. Today, detection and accurate structural analysis of these – generally transient – forms remain challenging, essentially because of the present limitations in temporal and spatial resolution of the analysis, which prevents rationalization (and hence control) of crystallization processes.
In our group, we develop dynamic nuclear polarization (DNP) solid-state NMR approaches to overcome these limitations. In this contribution, I will present some of our latest results showing that cryogenic MAS NMR [1] combined with the sensitivity enhancement provided by DNP [2] can be an efficient way of monitoring the structural evolution of crystallizing solutions with atomic-scale resolution on a time scale of a few minutes. I will discuss current approaches and recent developments allowing to detect and characterize transient, metastable phases formed at the early stages of crystallization through the use of tailored DNP polarizing agents [3].
[1] P. Cerreia-Vioglio, G. Mollica, M. Juramy, C.E. Hughes, P.A. Williams, F. Ziarelli, S. Viel, P. Thureau, K.D.M. Harris, Angew. Chem. Int. Ed. 57, 6619 (2018)
[2] P. Cerreia-Vioglio, P. Thureau, M. Juramy, F. Ziarelli, S. Viel, P.A. Williams, C.E. Hughes, K.D.M. Harris, G. Mollica J. Phys. Chem. Lett. 10, 1505 (2019)
[3] M. Juramy, R. Chèvre, P. Cerreia-Vioglio, F. Ziarelli, E. Besson, S. Gastaldi, S. Viel, P. Thureau, K.D.M. Harris, G. Mollica J. Am. Chem. Soc. 143, 16, 6095 (2021)