Methyl mercury uptake by free and immobilized cyanobacterium

Abstract

Methyl mercury uptake in free cells and different immobilizates of the cyanobacteriumNostoc calcicola has been examined. The general growth of the immobilized cyanobacterial cells could be negatively correlated with methyl mercury uptake. Alginate spheres proved most efficient in terms of uptake rate (0.48 nmol mg protein⁻¹ min⁻¹, 10 min) and total bioaccumulation (10.71 nmol mg protein⁻¹, 1 h) with a bioconcentration factor of 3.3×10³. Alginate biofilms showed a faster methyl mercury accumulation rate (0.83 nmol mg protein⁻¹ min⁻¹, 10 min) with a saturation of 10.28 nmol mg protein⁻¹ reached within only 30 min (bioconcentration factor, 3.1×10³). Foam preparations with a slow initial uptake approximated biofilms but were characterized by a lower bioconcentration factor (2.8×10³). Free cells, in comparison, maintained the initial slow rate of uptake (0.62 nmol mg protein⁻¹ min⁻¹, 10 min), saturating at 30 min (8.81 nmol mg protein⁻¹), and the resultant lowest bioconcentration factor (2.7×10³). Cell ageing (30 days) brought a drastic reduction (3-fold) in organomercury uptake by free cells while alginate spheres maintained the same potential. Foam preparations of the same age showed a significant improvement in methyl mercury uptake followed by only a marginal decline in alginate biofilms. Data are discussed in the light of the physiological efficiency and longevity of immobilized cells.