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

Area of Science:

• Microbiology
• Environmental Science
• Radiochemistry

Background:

• Siderophores are high-affinity iron-chelating molecules produced by microorganisms.
• Understanding metal-microbe interactions is crucial for environmental remediation and risk assessment.
• Desferrioxamine-B (DFOB) is a well-characterized siderophore involved in iron transport.

Purpose of the Study:

• To investigate the uptake of plutonium (Pu) and uranium (U) by the soil bacterium Microbacterium flavescens (JG-9) mediated by the siderophore DFOB.
• To determine if M. flavescens can utilize Pu-DFOB and U-DFOB complexes, similar to Fe-DFOB.
• To elucidate the mechanisms and competition involved in the uptake of metal-DFOB complexes.

Main Methods:

• Bacterial cultures of M. flavescens (JG-9) were incubated with various metal complexes: U(VI)-DFOB, Fe(III)-DFOB, and Pu(IV)-DFOB.
• Uptake was quantified by measuring the accumulation of metals within metabolically active and inactive bacterial cells.
• Competitive uptake experiments were performed by co-incubating Fe(III)-DFOB and Pu(IV)-DFOB.

Main Results:

• M. flavescens actively took up Fe(III)-DFOB and Pu(IV)-DFOB, but not U(VI)-DFOB or NTA complexes.
• Uptake of both Fe(III)-DFOB and Pu(IV)-DFOB required metabolically active bacteria.
• Fe(III)-DFOB and Pu(IV)-DFOB mutually inhibited each other's uptake, indicating shared transport pathways.
• Pu uptake was significantly slower and lower in cumulative amount compared to Fe uptake.

Conclusions:

• M. flavescens possesses a transport system that recognizes and internalizes Pu(IV)-DFOB, similar to Fe(III)-DFOB.
• This suggests that microbial iron uptake systems may play a role in the environmental mobility and bioavailability of plutonium.
• The findings indicate that siderophore complexes of tetravalent metals can be recognized by Fe-siderophore uptake proteins in bacteria.