Formation of Se(0) nanoparticles by Azospirillum brasilense

In the present study we investigated the reduction of SeO32− by Azospirillum brasilense. The formation of fairly soluble Se(0) nano-particles during this process might be of interest for both bioremediation of Se-contaminated sites and for nanobiotechnology. After A.brasilense being exposed to Se(IV), the bacterial growth continued subsequent to a prolonged lag-phase. After a cultivation time of 3 days, a clearly reddish staining of the sample was observed and a bright red precipitate occurred, indicating the formation of Se(0) nano-particles. The SEM-EDX spectra derived from the nano-spheres indicated that they mainly consist of selenium. In addition, only 10 % of the initial Se(IV) concentrations was recoverd in culture media by means of HG-AAS, indicating a Se(IV) removal from the media. The isolated and resuspended Se(0) nanoparticles showed a long time stability of some hours, which is sufficient for the PCS and the zeta potential measurements. In contrast, Se(0) chemically formed by reduction with hydroxylamine solution produced amorphous aggregates with a rapid sedimentation behavior. The PCS measurement and the SEM imaging of the Se(0) particles showed a particle size distribution between 100 and 300 nm with an averaged particle diameter of 200 nm. The isoelectric point of Se(0) particles was found at pH 2.8 ± 0.2. The preference of forming Se(0) particles with a negative charge agree very well with the literature [1].

[1] Dhanjal & Cameotra (2010) Microb. Cell Fact. 9,1-11.