The Synthesis of Elemental Selenium Particles by the Cyanobacterium Synechococcus leopoliensis
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In the present study the light dependent biosynthesis of spherical red elemental selenium Se(0) granules (average size of 220 nm) by the cyanobacterium Synechococcus leopoliensis when exposed to high selenite concentrations for 9 days was investigated. The particles were identified as Se(0) by energy dispersive x-ray spectroscopy (EDX) analysis and were localized between the periplasmic space and the cell surface through light and environmental scanning electron microscopy (ESEM). The amount of selenite reduced to Se(0) increased with increasing culture density and less selenite remained in the cultures accordingly. Selenite treated cultures lost their characteristic pigments and turned from green to orange by day 5 and a concomitant increase in the buoyant cell density was observed over the treatment period. The potential abiotic and biotic reactions that may have produced Se(0) in the cyanobacteria are discussed.