Dynamic changes in carbonate chemistry in the microenvironment around single marine phytoplankton cells

Abdul Chrachri,Glen L Wheeler,Kevin Flynn,Colin Brownlee,Brian M Hopkinson

doi:10.1038/s41467-017-02426-y

Abstract

Photosynthesis by marine diatoms plays a major role in the global carbon cycle, although the precise mechanisms of dissolved inorganic carbon (DIC) uptake remain unclear. A lack of direct measurements of carbonate chemistry at the cell surface has led to uncertainty over the underlying membrane transport processes and the role of external carbonic anhydrase (eCA). Here we identify rapid and substantial photosynthesis-driven increases in pH and [CO32−] primarily due to the activity of eCA at the cell surface of the large diatom Odontella sinensis using direct simultaneous microelectrode measurements of pH and CO32− along with modelling of cell surface inorganic carbonate chemistry. Our results show that eCA acts to maintain cell surface CO2 concentrations, making a major contribution to DIC supply in O. sinensis. Carbonate chemistry at the cell surface is therefore highly dynamic and strongly dependent on cell size, morphology and the carbonate chemistry of the bulk seawater.

Highlights

Photosynthesis by marine diatoms plays a major role in the global carbon cycle, the precise mechanisms of dissolved inorganic carbon (DIC) uptake remain unclear
Using ion-selective microelectrodes and selective inhibitors of external carbonic anhydrase (eCA), we demonstrate that eCA activity plays a major role in photosynthetic DIC uptake in O. sinensis and that eCA activity is primarily responsible for the light-dependent perturbations in carbonate chemistry at the cell surface
CO2 is slow and highly pH-dependent. This complexity has led to uncertainty over the mechanisms of photosynthetic DIC uptake in diatoms and in particular the role of eCA in enhancing the supply of CO2 to the cell surface[40]

Summary

Introduction

Photosynthesis by marine diatoms plays a major role in the global carbon cycle, the precise mechanisms of dissolved inorganic carbon (DIC) uptake remain unclear. A lack of direct measurements of carbonate chemistry at the cell surface has led to uncertainty over the underlying membrane transport processes and the role of external carbonic anhydrase (eCA). Like most other marine phytoplankton, diatoms need to operate a carbon concentrating mechanism (CCM) due to the low availability of CO2 (the substrate for carbon fixation by the enzyme RuBisCO) in the alkaline pH of seawater, with

Methods

Results

Conclusion