Abstract


Swearingen Jr., Jerry, Identification of Organo-tellurium and Organo-selenium Compounds in the Headspace Gases Above Genetically Modified Escherichia coli Amended with Tellurium and Selenium Salts. Master of Science (Chemistry), August 2005, Sam Houston State University, Huntsville, Texas, 83 pp. (pdf version of this thesis)

The purpose of this work was to identify organo-selenium and organo-tellurium compounds produced by genetically modified Escherichia coli cells that were amended with selenium or tellurium salts. The goals of this research were to see which genetic modifications were responsible for the production of the organo-chalcogen compounds. Experiments were designed to detect new, never previously reported compounds above the modified E. coli cultures.

Experiments were also performed to see if the change from aerobic to anaerobic growth conditions affected the bioremediation potential of Pseudomonas fluorescens K27. Recombinant E. coli cultures were amended with either tellurate, tellurite, selenate, or selenite or some combination of these salts. Experiments show that ORF 600 and 1VH (which contains ORF 600) produce organo-tellurium and organo-selenium compounds. Expression of ORF 600, which contains the gene encoding for a UbiE methyltransferase, resulted in production of organo-tellurium compounds when the clone was amended with tellurate but did not produce any organo-tellurium compounds when the clone was amended with tellurite.

Organo-tellurium compounds that were detected above tellurium amended cultures were dimethyl telluride, methanetellurol, dimethyl tellurenyl sulfide, and dimethyl ditelluride. The last three have never been reported before in the literature as bacterial products. Organo-selenium compounds that were detected were dimethyl selenide, dimethyl selenenyl sulfide, dimethyl diselenide, and dimethyl selenodisulfide. The oxidation state of selenium in the amendments did not affect the production of organo-selenium compounds.

Dimethyl selenodisulfide has never been detected in the headspace gases above bacterial cultures but was determined here; its structure was confirmed by GC/MS and compared to a similar mass spectrum found in the literature.

Detection of these volatile compounds was performed by using either gas chromatography-sulfur chemiluminescence detection or gas chromatography-mass spectrometry.

Sequentially switching from aerobic to anaerobic growth did not show any improvement or decline of the bioremediation potential of Pseudomonas fluorescens K27. Measurement of dissolved oxygen (D.O.) content of the culture media was done by a D.O. probe that measured the percent of oxygen saturation in the solution. A D.O. probe that measured the solution phase concentration of dissolved oxygen (mg/L) was also used.

KEY WORDS: Genetically modified E. coli, organo-selenium, organo-tellurium, aerobic/anaerobic growth, methyl transferase, dimethyl tellurenyl sulfide.

 

Thomas G. Chasteen
Thesis Director

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