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Cellular inorganic carbon fluxes in Trichodesmium: a combined approach using measurements and modelling.

Eichner M, Thoms S, Kranz SA, Rost B - J. Exp. Bot. (2014)

Bottom Line: Strong discrepancies were observed in CO2 leakage estimates obtained by MIMS and a (13)C-based approach, which further increased under elevated pCO2.These offsets could be explained by applying a model that comprises extracellular CO2 and HCO3 (-) fluxes as well as internal Ci cycling around the carboxysome via the CO2 uptake facilitator NDH-14.Our results highlight the importance of internal Ci cycling for (13)C composition as well as cellular energy budgets of Trichodesmium, which ought to be considered in process studies on climate change effects.

View Article: PubMed Central - PubMed

Affiliation: Marine Biogeosciences, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany meri.eichner@awi.de.

No MeSH data available.


Related in: MedlinePlus

Example showing the dependence of Ci fluxes measured by MIMS in Trichodesmium on the DIC concentration in the assay. Data shown were measured in the evening in a culture grown at 380 µatm pCO2 without NO3–. The shaded area denotes the range of acclimation DIC levels.
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Figure 2: Example showing the dependence of Ci fluxes measured by MIMS in Trichodesmium on the DIC concentration in the assay. Data shown were measured in the evening in a culture grown at 380 µatm pCO2 without NO3–. The shaded area denotes the range of acclimation DIC levels.

Mentions: MIMS measurements showed a highly efficient CCM with a high capacity for regulation of Ci affinity over the diurnal cycle as well as with different pCO2 levels, in agreement with previous studies on Trichodesmium (e.g. Kranz et al., 2009; Kranz et al., 2010). Half-saturation DIC concentrations for C fixation (K1/2) ranged between ~20 and 500 µmol DIC l–1 (Supplementary Figure S1), which is equivalent to ~0.2 and 4 µmol CO2 l–1 and is thus substantially lower than the KM of cyanobacterial RubisCO (105–185 µmol CO2 l–1; Badger et al., 1998). Taking the ratio of KM to K1/2 as a measure of CO2 accumulation in the vicinity of RubisCO (assuming a KM of 150 µmol CO2 l–1), our data suggest accumulation factors between ~35 and 900 and indicate that the degree of RubisCO saturation is always larger than 80%. Accordingly, under the applied external CO2 concentrations, concentrations in the carboxysome typically exceed 600 µmol CO2 l–1. The CCM was primarily based on active HCO3– uptake, accounting for 82±4% of gross Ci uptake (Table 1). As gross Ci uptake was approximately twice as high as net C fixation at acclimation DIC (~2100 µmol CO2 l–1), leakage measured by MIMS ranged between 0.3 and 0.7 (i.e. CO2 efflux equalled 30–70% of gross Ci uptake; Table 1). As a consequence of the high HCO3– contribution and the high CO2 efflux, the net fluxes of CO2 were generally directed out of the cell (cf. negative values for net CO2 uptake: Table 1, Fig. 2).


Cellular inorganic carbon fluxes in Trichodesmium: a combined approach using measurements and modelling.

Eichner M, Thoms S, Kranz SA, Rost B - J. Exp. Bot. (2014)

Example showing the dependence of Ci fluxes measured by MIMS in Trichodesmium on the DIC concentration in the assay. Data shown were measured in the evening in a culture grown at 380 µatm pCO2 without NO3–. The shaded area denotes the range of acclimation DIC levels.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4321539&req=5

Figure 2: Example showing the dependence of Ci fluxes measured by MIMS in Trichodesmium on the DIC concentration in the assay. Data shown were measured in the evening in a culture grown at 380 µatm pCO2 without NO3–. The shaded area denotes the range of acclimation DIC levels.
Mentions: MIMS measurements showed a highly efficient CCM with a high capacity for regulation of Ci affinity over the diurnal cycle as well as with different pCO2 levels, in agreement with previous studies on Trichodesmium (e.g. Kranz et al., 2009; Kranz et al., 2010). Half-saturation DIC concentrations for C fixation (K1/2) ranged between ~20 and 500 µmol DIC l–1 (Supplementary Figure S1), which is equivalent to ~0.2 and 4 µmol CO2 l–1 and is thus substantially lower than the KM of cyanobacterial RubisCO (105–185 µmol CO2 l–1; Badger et al., 1998). Taking the ratio of KM to K1/2 as a measure of CO2 accumulation in the vicinity of RubisCO (assuming a KM of 150 µmol CO2 l–1), our data suggest accumulation factors between ~35 and 900 and indicate that the degree of RubisCO saturation is always larger than 80%. Accordingly, under the applied external CO2 concentrations, concentrations in the carboxysome typically exceed 600 µmol CO2 l–1. The CCM was primarily based on active HCO3– uptake, accounting for 82±4% of gross Ci uptake (Table 1). As gross Ci uptake was approximately twice as high as net C fixation at acclimation DIC (~2100 µmol CO2 l–1), leakage measured by MIMS ranged between 0.3 and 0.7 (i.e. CO2 efflux equalled 30–70% of gross Ci uptake; Table 1). As a consequence of the high HCO3– contribution and the high CO2 efflux, the net fluxes of CO2 were generally directed out of the cell (cf. negative values for net CO2 uptake: Table 1, Fig. 2).

Bottom Line: Strong discrepancies were observed in CO2 leakage estimates obtained by MIMS and a (13)C-based approach, which further increased under elevated pCO2.These offsets could be explained by applying a model that comprises extracellular CO2 and HCO3 (-) fluxes as well as internal Ci cycling around the carboxysome via the CO2 uptake facilitator NDH-14.Our results highlight the importance of internal Ci cycling for (13)C composition as well as cellular energy budgets of Trichodesmium, which ought to be considered in process studies on climate change effects.

View Article: PubMed Central - PubMed

Affiliation: Marine Biogeosciences, Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany meri.eichner@awi.de.

No MeSH data available.


Related in: MedlinePlus