Dataset for: Temperature sensitivity of carbon concentrating mechanisms in the diatom Phaeodactylum tricornutum

Marine diatoms are key primary producers across diverse habitats in the
global ocean. Diatoms rely on a biophysical carbon concentrating mechanism
(CCM) to supply high concentrations of CO2 around their carboxylating
enzyme, RuBisCO. The necessity and energetic cost of the CCM are likely to
be highly sensitive to temperature, as temperature impacts CO2
concentration, diffusivity, and the kinetics of CCM components. Here, we
used membrane inlet mass spectrometry (MIMS) and modeling to capture
temperature regulation of the CCM in the diatom Phaeodactylum tricornutum
(Pt). We found that enhanced carbon fixation rates by Pt at elevated
temperatures were accompanied by increased CCM activity capable of
maintaining RuBisCO close to CO2 saturation but that the mechanism varied.
At 10 and 18 °C, diffusion of CO2 into the cell, driven by Pt’s
‘chloroplast pump’ was the major inorganic carbon source. However, at 18
°C, upregulation of the chloroplast pump enhanced (while retaining the
proportion of) both diffusive CO2 and active HCO3- uptake into the
cytosol, and significantly increased chloroplast HCO3- concentrations. In
contrast, at 25 °C, compared to 18 °C, the chloroplast pump had only a
slight increase in activity. While diffusive uptake of CO2 into the cell
remained constant, active HCO3- uptake across the cell membrane increased
resulting in Pt depending equally on both CO2 and HCO3- as inorganic
carbon sources. Despite changes in the CCM, the overall rate of active
carbon transport remained double that of carbon fixation across all
temperatures tested. The implication of the energetic cost of the Pt CCM
in response to increasing temperatures was discussed.