Following the Headspace Production of Organometalloids
Produced by a Facultative Anaerobe Amended with Metalloidal Salts

Alan Stone, Verena Van Fleet-Stalder, and Thomas G. Chasteen

Department of Chemistry, Sam Houston State University
Huntsville, TX 77341-2117 

A liquid culture of denitrifying bacteria was amended with sodium selenate in a commercial fermentor that allowed for monitoring of pH, dissolved oxygen, temperature, and solution and headspace content. In anaerobic cultures of Pseudomonas fluorescens K27 grown on a complex medium with nitrate as electron acceptor, biological reduction and methylation of selenate oxyanion (SeO₄^2-) led to the production of dimethyl selenide and dimethyl diselenide. Simultaneously, methanethiol and organosulfides, dimethyl sulfide, -disulfide and -trisulfide, were also biologically produced since Se-free cultures yielded these same organosulfur species. The headspace concentration of dimethyl selenide and dimethyl diselenide increased over the entire time course; however, organosulfur levels waxed and waned unsystematically. The pH of both Se-amended and Se-free cultures crept up (7.2 to 7.5) over the 9 hour experimental time course, and reducing power, as measured by a polarographic probe, increased measurably as the cultures entered the mid-log phase.
 
Data taken the week before this meeting (and presented in Dallas) show that 0.1 mM tellurite amended cultures of this bacterium produce dimethyl telluride in a relatively smooth increase correlated with cell population. Concentrations of tellurite ten times smaller than those of the selenate experiments described above produce much smaller amounts of total biomass by log phase (as measured by optical density). Also black elemental tellurium (Te⁰) was produced in the latter stages of growth. This work was carried out by M. Akpolat and L. Eriksen, Jr. in our lab.