View source for Cobalamin uptake with 57Cobalt-B12

{{BreadcrumbsNutrients}}

* [[Page authors|Page authors]]: [[PRIMO]]
* [[Responsible curator|Responsible curator]]:  [[User:Hagi BucknWise|Hagen Buck-Wiese]]
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! Cobalamin uptake (<sup>57</sup>Co-B12)
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| '''Approach:''' radiotracer (<sup>57</sup>Co-labelled cobalamin) incubation
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| '''Context:''' incubation, lab
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| '''Spatial scale:''' point sample
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| '''Temporal scale:''' 4–24 h
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| '''Units:''' mol cell<sup>-1</sup> d<sup>-1</sup>; mol L<sup>-1</sup> d<sup>-1</sup>; mol mol C<sup>-1</sup> d<sup>-1</sup>
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| '''Community captured:''' all (usually > 0.2 or 0.7 µm)
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| '''Co-measurements:''' biomass (Chl, cells, POC, cell volume)
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== Method Overview ==

Cobalamin (vitamin B<sub>12</sub>) uptake rates are measured using <sup>57</sup>Co-labelled cyanocobalamin (<sup>57</sup>Co-B12; half-life ~271 days, gamma emitter). The radiolabelled cobalamin is added to seawater at tracer concentrations under trace-metal-clean conditions and equilibrated with the sample. After incubation (4–24 h), cells are collected on filters, rinsed to remove surface-adsorbed cobalamin, and counted by gamma spectrometry. Uptake rates are calculated from the fraction of <sup>57</sup>Co-B12 incorporated relative to total dissolved <sup>57</sup>Co-B12<ref name="Bertrand2011">Bertrand, E. M., Saito, M. A., Rose, J. M., Riesselman, C. R., Lohan, M. C., Noble, A. E., Lee, P. A., & DiTullio, G. R. (2011). Vitamin B<sub>12</sub> and iron colimitation of phytoplankton growth in the Ross Sea. ''Limnology and Oceanography'', 56(4), 1079–1091. https://doi.org/10.3389/fmicb.2011.00160</ref>.

Cobalamin is an essential cofactor that many phytoplankton cannot synthesize and must obtain from cobalamin-producing bacteria, making uptake rate measurements central to understanding phytoplankton–bacteria vitamin interactions.

=== Scale of measurement ===

Point sample after 4–24 h of incubation under trace-metal-clean conditions.

=== Data generated ===

Cobalamin uptake rates (mol cell<sup>-1</sup> d<sup>-1</sup> or mol L<sup>-1</sup> d<sup>-1</sup>). Combined with cellular B<sub>12</sub> quotas, the community's vitamin B<sub>12</sub> demand and turnover can be characterized.

=== Units & currency ===

Units are mol cell<sup>-1</sup> d<sup>-1</sup>, mol L<sup>-1</sup> d<sup>-1</sup>, or mol mol C<sup>-1</sup> d<sup>-1</sup>. The currency is Co (as cobalamin).

=== Sample size ===

Typical samples are < 1 L in volume.

=== Repositories & databases ===

== Limitations ==

The method assumes that <sup>57</sup>Co remains associated with the intact cobalamin molecule throughout the incubation (no degradation of cobalamin to other Co-containing compounds). In practice, some B<sub>12</sub> degradation can occur, leading to uptake of <sup>57</sup>Co in non-cobalamin forms. Natural cobalamin-binding proteins in seawater can compete with cellular uptake, and their effect must be considered when estimating bioavailable cobalamin.

== Example Applications & Protocols ==

=== Classic examples ===
* Bertrand et al. (2011) ''Vitamin B<sub>12</sub> and iron colimitation of phytoplankton growth in the Ross Sea'' <ref name="Bertrand2011" />

=== Recent applications ===
*

=== Common calculations/conversions ===
* B<sub>12</sub> uptake rate = (cpm<sub>cells</sub> / cpm<sub>dissolved</sub>) × [B<sub>12,dissolved</sub>] / incubation time.

== References ==

[[Category:Main Pages|Model types]]