Minimal cobalt metabolism in the marine cyanobacterium Prochlorococcus

Abstract

<jats:p>Despite very low concentrations of cobalt in marine waters, cyanobacteria in the genus<jats:italic>Prochlorococcus</jats:italic>retain the genetic machinery for the synthesis and use of cobalt-bearing cofactors (cobalamins) in their genomes. We explore cobalt metabolism in a<jats:italic>Prochlorococcus</jats:italic>isolate from the equatorial Pacific Ocean (strain MIT9215) through a series of growth experiments under iron- and cobalt-limiting conditions. Metal uptake rates, quantitative proteomic measurements of cobalamin-dependent enzymes, and theoretical calculations all indicate that<jats:italic>Prochlorococcus</jats:italic>MIT9215 can sustain growth with less than 50 cobalt atoms per cell, ∼100-fold lower than minimum iron requirements for these cells (∼5,100 atoms per cell). Quantitative descriptions of<jats:italic>Prochlorococcus</jats:italic>cobalt limitation are used to interpret the cobalt distribution in the equatorial Pacific Ocean, where surface concentrations are among the lowest measured globally but<jats:italic>Prochlorococcus</jats:italic>biomass is high. A low minimum cobalt quota ensures that other nutrients, notably iron, will be exhausted before cobalt can be fully depleted, helping to explain the persistence of cobalt-dependent metabolism in marine cyanobacteria.</jats:p>

Metabolic versatility of the nitrite-oxidizing bacterium Nitrospira marina and its proteomic response to oxygen-limited conditions

“…Prochlorococcus [78] (Table 1) despite only having ã two-fold greater cell volume, consistent with the importance of B 12 nutrition to N. marina. Moreover, this salvage acquisition mode is interesting in the context of dissolved cobalt speciation, which is complexed by strong organic ligands hypothesized to include B 12 precursors or degradation products [79].…”

The requirement for cobalt in vitamin B12: A paradigm for protein metalation

“…What is the advantage of a corrin ring over the versatile porphyrin macrocycle of heme, and what is it about cobalt that so suits it for B 12 -dependent processes? This is particularly relevant given that (i) the availability of cobalt as a trace element varies significantly on both land and in water [ [23] , [24] , [25] ], and (ii) that the corrin ring is so difficult to make [ [26] , [27] , [28] ]. The main driving force for utilising cobalt is the chemistry that is mediated by the metal.…”

Independent iron and light limitation in a low-light-adapted Prochlorococcus from the deep chlorophyll maximum

“…This interpretation is supported by the <15% difference in chlorophyll a :C ratios of Fe-replete Prochlorococcus MIT1214 grown at 0.22 and 1.7 mol photon m −2 day −1 (Fig. 1d ; Fe′ >150 pM; ANOVA with post-hoc Tukey test, p > 0.05), and by the much higher IUE achieved by the high-light adapted strain Prochlorococcus MIT9215 (1.5 × 10 5 mol C mol Fe −1 day −1 ) when grown at greater irradiance [ 11 ].…”