Siderophore mediated plutonium accumulation by Microbacterium flavescens (JG-9)

Uptake of plutonium and uranium mediated by the siderophore desferrioxamine -B (DFOB) has been studied for the common soil aerobe Microbacterium flaves cens (JG-9). M. flavescens does not bind or take up nitrilotriacetic acid ( NTA) complexes of U(VI), Fe(III), or Pu(IV) or U(VI)-DFOB but does take up Fe(III)-DFOB and Pu(IV)-DFOB. Pu(IV)-DFOB and Fe(III)-DFOB accumulations ar e similar: only living and metabolically active bacteria take up these meta l-siderophore complexes. The Fe(III)-DFOB and Pu(IV)-DFOB complexes mutuall y inhibit uptake of the other, indicating that they compete for shared bind ing sites or uptake proteins. However, Pu uptake is much slower than Fe upt ake, and cumulative Pu uptake is less than Fe, 1.0 nmol of Fe vs 0.25 nmol of Pu per mg of dry weight bacteria. The Pu(IV)-DFOB interactions with M fl avescens suggest that Pu-siderophore complexes could generally be recognize d by Fe-siderophore uptake systems of many bacteria, fungi, or plants, ther eby affecting Pu environmental mobility and distribution. The results also suggest that the siderophore complexes of tetravalent metals can be recogni zed by Fe-siderophore uptake proteins.