Bioaccumulation of yttrium in Pseudomonas fluorescens and the role of the outer membrane component(s)
Department of Chemistry and Biochemistry, Laurentian University, Sudbury, Ontario, Canada. Microbios
Pseudomonas fluorescens was grown in millimolar amounts of yttrium. The tolerance to yttrium appeared to be mediated by the ability of the organism to accumulate the trivalent metal predominantly in the outer membrane component(s). At the stationary phase of growth, 65 to 70% of the metal was associated with the constituent(s) of the outer membrane. Treatment with 2 mM (EDTA) did not release the metal. Incubation of the outer membrane fraction with yttrium led to further accumulation of the metal. The outer membrane equivalent to 1 mg of protein was shown to immobilize 175 microg of yttrium. There was no significant variation in uronic acid and the lipid contents of the control and yttrium-stressed cells as monitored by colorimetric assays. The protein profiles of the outer and inner membrane components obtained from the control and metal-stressed cells showed marked variations as revealed by sodium dodecyl sulphate polyacrylamide gel electrophoretic analysis.
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ABSTRACT: We studied the biodegradation of Eu(III)–malic acid complexes by Pseudomonas fluorescens. The bacterium degraded 10 mM acid in the presence of 0.05, 0.1, and 0.2 mM Eu(III), and also in its absence. The rate of degradation increased with decreasing ratios of Eu(III) to malic acid. These results suggest that the toxicity of Eu(III) can be masked through its complexation with malic acid. Unidentified metabolites associated with Eu(III) were produced as malic acid was broken down. Analyses by electrospray ionization mass spectrometry (ESI-MS) showed that one of them was pyruvic acid. Our findings suggest that the metabolites can influence the environmental behavior of Eu(III) by forming complexes with it.
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ABSTRACT: We present distribution coefficients, log iKS, for the sorption of yttrium and the rare earth elements (YREEs) on BCR-279, a dehydrated tissue homogenate of a marine macroalga, Ulva lactuca, resembling materials featured in chemical engineering studies aimed at designing renewable biosorbents. Sorption experiments were conducted in NaCl solutions of different ionic strength (0.05, 0.5, and 5.0 M) at T = 25 °C over the pH range 2.7-8.5. Distribution coefficients based on separation of the dissolved and particulate phase by conventional filtration (<0.22 μm) were corrected for the effect of colloid-bound YREEs (>3 kDa) using an existing pH-dependent model. Colloid-corrected values were renormalized to free-cation concentrations by accounting for YREE hydrolysis and chloride complexation. At each ionic strength, the pH dependence of the renormalized values is accurately described with a non-electrostatic surface complexation model (SCM) that incorporates YREE binding to three monoprotic functional groups, previously characterized by alkalimetric titration, as well as binding of YREE-hydroxide complexes (MOH2+) to the least acidic one (pKa ∼ 9.5).
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