​Oscar Guadayol

​U. Lincoln (UK)
 

An engineering tool for a phytoplankton cell
 

Viscosity is critically important to planktonic life, as it affects both the rate of diffusion of molecules and the motility of microbes. And yet, it is a property that has been traditionally neglected by physical oceanography because water viscosity is well constrained by temperature, salinity and pressure. We know, however, that exopolymeric substances (EPS) released by marine organisms can alter the bulk viscosity of seawater at large scales. The role of EPS in physically structuring the microscale environment remains hypothetical. We used microrheological techniques to map viscosity with micron resolution around phytoplankton cells and inside aggregates, revealing the existence of steep gradients at the microscale. These gradients, as our numerical models show, can alter the dynamics and spatial structure of the chemical landscape and affect the motility and chemotactic performance of bacteria. Altogether this suggests that secreting EPS could be a good strategy for a phytoplankton cell to scaffold the phycosphere and optimize both resource acquisition and interactions with bacteria.

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