Identification of biogenic dimethyl selenodisulfide in the headspace gases above genetically modified Escherichia coli

Escherichia coli JM109 cells were modified to express the genes encoded in a 3.8-kb chromosomal DNA fragment from a metalloid-resistant thermophile, Geobacillus stearothermophilus V. Manual headspace extraction was used to collect the gases for gas chromatography with fluorine-induced sulfur chemiluminescence analysis while solid-phase microextraction was used for sample collection in gas chromatography/mass spectrometry (GC/MS) analysis. When grown in the presence of selenate or selenite, these bacteria produced both organo-sulfur and organo-selenium in the headspace gases above the cultures. Organo-sulfur compounds detected were methanethiol, dimethyl sulfide, dimethyl disulfide, and dimethyl trisulfide. Organo-selenium compounds detected were dimethyl selenide and dimethyl diselenide. Two mixed sulfur-selenium compounds, dimethyl selenenyl sulfide and a chromatographically late-eluting compound, were detected. Dimethyl selenodisulfide, CH₃SeSSCH₃, and dimethyl bis(thio)selenide, CH₃SSeSCH₃, were synthesized and analyzed by GC/MS and fluorine-induced chemiluminescence to determine which corresponded to the late-eluting compound that was bacterially produced. CH ₃SeSSCH₃ was positively identified as the compound detected in bacterial headspace above Se-amended cultures. Using GC retention times, the boiling point of CH₃SeSSCH₃ was estimated to be approximately 192°C. This is the first report of CH₃SeSSCH ₃ produced by bacterial cultures.