Growth
of <i>Desulfovibrio vulgaris</i> When
Respiring U(VI) and Characterization of Biogenic Uraninite
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Abstract
The
capacity of <i>Desulfovibrio vulgaris</i> to reduce
U(VI) was studied previously with nongrowth conditions involving a
high biomass concentration; thus, bacterial growth through respiration
of U(VI) was not proven. In this study, we conducted a series of batch
tests on U(VI) reduction by <i>D. vulgaris</i> at a low
initial biomass (10 to 20 mg/L of protein) that could reveal biomass
growth. <i>D. vulgaris</i> grew with U(VI) respiration alone,
as well as with simultaneous sulfate reduction. Patterns of growth
kinetics and solids production were affected by sulfate and Fe<sup>2+</sup>. Biogenic sulfide nonenzymatically reduced 76% of the U(VI)
and greatly enhanced the overall reduction rate in the absence of
Fe<sup>2+</sup> but was rapidly scavenged by Fe<sup>2+</sup> to form
FeS in the presence of Fe<sup>2+</sup>. Biogenic U solids were uraninite
(UO<sub>2</sub>) nanocrystallites associated with 20 mg/g biomass
as protein. The crystallite thickness of UO<sub>2</sub> was 4 to 5
nm without Fe<sup>2+</sup> but was <1.4 nm in the presence of Fe<sup>2+</sup>, indicating poor crystallization inhibited by adsorbed Fe<sup>2+</sup> and other amorphous Fe solids, such as FeS or FeCO<sub>3</sub>. This work fills critical gaps in understanding the metabolic utilization
of U by microorganisms and formation of UO<sub>2</sub> solids in bioremediation
sites