Investigation of the interactions between selected bacteria and selenium oxyanions

The microbial reduction of soluble selenium cations into its insoluble elemental form presents a unique opportunity to decontaminate industrial waste. We tested two strains of Bacillus sp. (JG-B5T, JG-B41) isolated from a uranium mining waste pile in Johanngeorgenstadt (Saxony) for their potential capacity to reduce selenium. A third species (Shewanella oneidensis) with a known reduction capacity is used as reference organism.
The microbial behavior of the bacteria under the influence of sodium selenite and selenate was observed. This included recording growth curves, pH alteration and changes in redox potential. The bacteria displayed differential growth when confronted with 2.5 mM selenite (Fig. 1) and selenate compared to controls. The content of the water soluble oxyanions was analyzed in the supernatant using inductively coupled plasma optical emission spectrometry. All selected strains have the ability to reduce selenite, whereas a reaction with selenate was not observed.
In addition we have observed and characterized the extracellular matrix focused on organic acids via High Performance Liquid Chromatography during the trial period. So far, the results indicate that two of the selected strains rely on different mechanisms.
The produced particles (Fig. 2) were isolated from the bacterial matrix and analyzed with Scanning electron microscopy with energy dispersive X-ray spectroscopy, by Raman spectroscopy, and Dynamic Light Scattering. With that we can determine their particle size, the type of bonding involved and their elemental compositions. The Raman spectra have already given indications for Se8-ring formation. X-ray analyses will reveal if other elements, like sulfur, are incorporated.After investigating the interaction of the selected strains with selenium in a defined medium, we will perform trials with real wastewater to test and validate our laboratory results under industrial conditions.
Reactions between selenium and microorganisms can significantly influence its transport behavior in the bio- and geosphere. Furthermore these metalloid-bacteria interactions can be used for various biotechnological applications.