Microrheology reveals microscale viscosity gradients in planktonic systems

Guadayol, Òscar, Mendonca, Tania, Segura-Noguera, Mariona , Wright, Amanda J, Tassieri, Manlio and Humphries, Stuart (2021) Microrheology reveals microscale viscosity gradients in planktonic systems. Proceedings of the National Academy of Sciences, 118 (1). e2011389118. ISSN 0027-8424

Full content URL: https://doi.org/10.1073/pnas.2011389118

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Microrheology reveals microscale viscosity gradients in planktonic systems
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Abstract

Microbial activity in planktonic systems creates a dynamic and heterogeneous microscale seascape that harbors a diverse community of microorganisms and ecological interactions of global significance. In recent decades great effort has been put into understanding this complex system, particularly focusing on the role of chemical patchiness, while overlooking a physical parameter that governs microbial life and is affected by biological activity: viscosity. Here we reveal spatial heterogeneity of viscosity in planktonic systems by using microrheological techniques that allow measurement of viscosity at length scales relevant to microorganisms. We show the viscous nature and the spatial extent of the phycosphere, the region surrounding phytoplankton. In ~45% of the phytoplankton cells analyzed we detected increases in viscosity that extended up to 30 μm away from the cell with up to 40 times the viscosity of seawater. We show also how these gradients of viscosity can be amplified around a lysing phytoplankton cell as its viscous contents leak away. Finally, we report conservative estimates of viscosity inside marine aggregates, hotspots of microbial activity, more than an order of magnitude higher than in seawater. Since the diffusivities of dissolved molecules, particles and microorganisms are inversely related to viscosity, microheterogeneity in viscosity alters the microscale distribution of microorganisms and their resources, with pervasive implications for the functioning of the planktonic ecosystem. Increasing viscosities impacts ecological interactions and processes, such as nutrient uptake, chemotaxis and particle encounter, that occur at the microscale but influence carbon and nutrient cycles at a global scale.

Keywords:Microscale patchiness, phytoplankton, extracellular polymeric substances (EPS), viscosity, passive microrheology
Subjects:C Biological Sciences > C161 Marine Biology
C Biological Sciences > C160 Marine/Freshwater Biology
C Biological Sciences > C500 Microbiology
Divisions:College of Science > School of Life Sciences
ID Code:43191
Deposited On:11 Dec 2020 13:01

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