Dataset Information

Interaction of Uranium with Bacterial Cell Surfaces: Inferences from Phosphatase-Mediated Uranium Precipitation.

ABSTRACT: Deinococcus radiodurans and Escherichia coli expressing either PhoN, a periplasmic acid phosphatase, or PhoK, an extracellular alkaline phosphatase, were evaluated for uranium (U) bioprecipitation under two specific geochemical conditions (GCs): (i) a carbonate-deficient condition at near-neutral pH (GC1), and (ii) a carbonate-abundant condition at alkaline pH (GC2). Transmission electron microscopy revealed that recombinant cells expressing PhoN/PhoK formed cell-associated uranyl phosphate precipitate under GC1, whereas the same cells displayed extracellular precipitation under GC2. These results implied that the cell-bound or extracellular location of the precipitate was governed by the uranyl species prevalent at that particular GC, rather than the location of phosphatase. MINTEQ modeling predicted the formation of predominantly positively charged uranium hydroxide ions under GC1 and negatively charged uranyl carbonate-hydroxide complexes under GC2. Both microbes adsorbed 6- to 10-fold more U under GC1 than under GC2, suggesting that higher biosorption of U to the bacterial cell surface under GC1 may lead to cell-associated U precipitation. In contrast, at alkaline pH and in the presence of excess carbonate under GC2, poor biosorption of negatively charged uranyl carbonate complexes on the cell surface might have resulted in extracellular precipitation. The toxicity of U observed under GC1 being higher than that under GC2 could also be attributed to the preferential adsorption of U on cell surfaces under GC1. This work provides a vivid description of the interaction of U complexes with bacterial cells. The findings have implications for the toxicity of various U species and for developing biological aqueous effluent waste treatment strategies.The present study provides illustrative insights into the interaction of uranium (U) complexes with recombinant bacterial cells overexpressing phosphatases. This work demonstrates the effects of aqueous speciation of U on the biosorption of U and the localization pattern of uranyl phosphate precipitated as a result of phosphatase action. Transmission electron microscopy revealed that location of uranyl phosphate (cell associated or extracellular) was primarily influenced by aqueous uranyl species present under the given geochemical conditions. The data would be useful for understanding the toxicity of U under different geochemical conditions. Since cell-associated precipitation of metal facilitates easy downstream processing by simple gravity-based settling down of metal-loaded cells, compared to cumbersome separation techniques, the results from this study are of considerable relevance to effluent treatment using such cells.

SUBMITTER: Kulkarni S

PROVIDER: S-EPMC4968550 | biostudies-literature | 2016 Aug

REPOSITORIES: biostudies-literature

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Interaction of Uranium with Bacterial Cell Surfaces: Inferences from Phosphatase-Mediated Uranium Precipitation.

Kulkarni Sayali S Misra Chitra Seetharam CS Gupta Alka A Ballal Anand A Apte Shree Kumar SK

Applied and environmental microbiology 20160729 16

<h4>Unlabelled</h4>Deinococcus radiodurans and Escherichia coli expressing either PhoN, a periplasmic acid phosphatase, or PhoK, an extracellular alkaline phosphatase, were evaluated for uranium (U) bioprecipitation under two specific geochemical conditions (GCs): (i) a carbonate-deficient condition at near-neutral pH (GC1), and (ii) a carbonate-abundant condition at alkaline pH (GC2). Transmission electron microscopy revealed that recombinant cells expressing PhoN/PhoK formed cell-associated ur ...[more]

PMID: 27287317

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Project description:The bacterial flagellum is the motility organelle powered by a rotary motor. The rotor and stator elements of the motor are located in the cytoplasmic membrane and cytoplasm. The stator units assemble around the rotor, and an ion flux (typically H+ or Na+) conducted through a channel of the stator induces conformational changes that generate rotor torque. Electrostatic interactions between the stator protein PomA in Vibrio (MotA in Escherichia coli) and the rotor protein FliG have been shown by genetic analyses, but have not been demonstrated biochemically. Here, we used site-directed photo- and disulfide-crosslinking to provide direct evidence for the interaction. We introduced a UV-reactive amino acid, p-benzoyl-L-phenylalanine (pBPA), into the cytoplasmic region of PomA or the C-terminal region of FliG in intact cells. After UV irradiation, pBPA inserted at a number of positions in PomA formed a crosslink with FliG. PomA residue K89 gave the highest yield of crosslinks, suggesting that it is the PomA residue nearest to FliG. UV-induced crosslinking stopped motor rotation, and the isolated hook-basal body contained the crosslinked products. pBPA inserted to replace residues R281 or D288 in FliG formed crosslinks with the Escherichia coli stator protein, MotA. A cysteine residue introduced in place of PomA K89 formed disulfide crosslinks with cysteine inserted in place of FliG residues R281 and D288, and some other flanking positions. These results provide the first demonstration of direct physical interaction between specific residues in FliG and PomA/MotA.ImportanceThe bacterial flagellum is a unique organelle that functions as a rotary motor. The interaction between the stator and rotor is indispensable for stator assembly into the motor and the generation of motor torque. However, the interface of the stator-rotor interaction has only been defined by mutational analysis. Here, we detected the stator-rotor interaction using site-directed photo- and disulfide-crosslinking approaches. We identified several residues in the PomA stator, especially K89, that are in close proximity to the rotor. Moreover, we identified several pairs of stator and rotor residues that interact. This study directly demonstrates the nature of the stator-rotor interaction and suggests how stator units assemble around the rotor and generate torque in the bacterial flagellar motor.

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Dataset Information

Interaction of Uranium with Bacterial Cell Surfaces: Inferences from Phosphatase-Mediated Uranium Precipitation.

Publications

Interaction of Uranium with Bacterial Cell Surfaces: Inferences from Phosphatase-Mediated Uranium Precipitation.

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