A role for mrgA, a DPS family protein, in the internal transport of Fe in the cyanobacterium Synechocystis sp. PCC6803

The mrgA protein of the cyanobacterium Synechocystis sp. PCC6803 is a member of the DPS Fe storage protein family. The physiological role of this protein was studied using a disruption mutant in the mrgA gene (slr1894) and by measuring intracellular Fe quotas, 77K chlorophyll fluorescence and growth rates. It was found that the deletion of the mrgA gene did not impair the Fe storage capacity, as the intracellular Fe quotas of the ΔmrgA cells were comparable to those of the wild type. Furthermore, the cellular response to decreasing external Fe concentrations, as detected by the emergence of the CP43′ 77K fluorescence band, was similar in wild type and mutant cultures. On the other hand, a considerable slow down in the growth rate of ΔmrgA cultures was observed upon transfer from Fe replete to Fe depleted medium, indicating impeded utilization of the plentiful intracellular Fe. Based on these results, we suggest that mrgA plays an important role in the transport of intracellular Fe from storage (within bacterioferritins) to biosynthesis of metal cofactors throughout the cell's growth.