title: Substrate supply for calcite precipitation in Emiliania huxleyi: assessment of different model approaches.
abstract: Over the last four decades, different hypotheses of Ca(2+) and dissolved inorganic carbon transport to the intracellular site of calcite precipitation have been put forth for Emiliania huxleyi (Lohmann) Hay & Mohler. The objective of this study was to assess these hypotheses by means of mathematical models. It is shown that a vesicle-based Ca(2+) transport would require very high intravesicular Ca(2+) concentrations, high vesicle fusion frequencies as well as a fast membrane recycling inside the cell. Furthermore, a kinetic model for the calcification compartment is presented that describes the internal chemical environment in terms of carbonate chemistry including calcite precipitation. Substrates for calcite precipitation are transported with different stoichiometries across the compartment membrane. As a result, the carbonate chemistry inside the compartment changes and hence influences the calcification rate. Moreover, the effect of carbonic anhydrase (CA) activity within the compartment is analyzed. One very promising model version is based on a Ca(2+) /H(+) antiport, CO2 diffusion, and a CA inside the calcification compartment. Another promising model version is based on an import of Ca(2+) and HCO3 (-) and an export of H(+) .
authors.affiliation: Alfred Wegener Institute for Polar and Marine Research, Biogeosciences, Am Handelshafen 12, Bremerhaven, 27570, Germany.
authors.forename: Lena-Maria
authors.initials: LM
authors.lastname: Holtz
authors.affiliation: Alfred Wegener Institute for Polar and Marine Research, Biogeosciences, Am Handelshafen 12, Bremerhaven, 27570, Germany.
authors.forename: Silke
authors.initials: S
authors.lastname: Thoms
authors.affiliation: Department of Earth Sciences, Cambridge University, Downing St., Cambridge, CB2 3EQ, UK.
authors.forename: Gerald
authors.initials: G
authors.lastname: Langer
authors.affiliation: Alfred Wegener Institute for Polar and Marine Research, Biogeosciences, Am Handelshafen 12, Bremerhaven, 27570, Germany.
authors.forename: Dieter A
authors.initials: DA
authors.lastname: Wolf-Gladrow
keywords: Ca2+ transport; Calcification; biomineralization; coccolith formation; coccolith vesicle