Microbial transformations of selenite by methane-oxidizing bacteria

Abstract

Methane-oxidizing bacteria are well known for their role in the global methane cycle and their potential for microbial transformation of wide range of hydrocarbon and chlorinated hydrocarbon pollution. Recently, it has also emerged that methane-oxidizing bacteria interact with inorganic pollutants in the environment. Here, we report what we believe to be the first study of the interaction of pure strains of methane-oxidizing bacteria with selenite. Results indicate that the commonly used laboratory model strains of methane-oxidizing bacteria, Methylococcus capsulatus (Bath) and Methylosinus trichosporium OB3b, are both able to reduce the toxic selenite (SeO3 2−) but not selenate (SeO4 2−) to red spherical nanoparticulate elemental selenium (Se0), which was characterized via energy-dispersive X-ray spectroscopy (EDXS), X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The cultures also produced volatile selenium-containing species, which suggests that both strains may have an additional activity that can transform either Se0 or selenite into volatile methylated forms of selenium. Transmission electron microscopy (TEM) measurements and experiments with the cell fractions cytoplasm, cell wall and cell membrane show that the nanoparticles are formed mainly on the cell wall. Collectively, these results are promising for the use of methane-oxidizing bacteria for bioremediation or suggest possible uses in the production of selenium nanoparticles for biotechnology.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-017-8380-8) contains supplementary material, which is available to authorized users.

Chemical and structural characterization of SeIV biotransformations by Stenotrophomonas bentonitica into Se0 nanostructures and volatiles Se species

“…The Debye-Waller factor (σ 2 ) of this shell, ranging from 0.0030 to 0.0045 Å 2 in all samples, decrease with reaction time, suggesting an increase of structural order with time (see Table 1). This could explain, as reported by Eswayah et al, 17 the biotransformation of amorphous SeNPs (24 h) to trigonal Se nanostructures (72 h and 144 h). Attempts to fit the second Se-Se coordination shell at about 3.63-3.70 ± 0.02 Å failed due to the small amplitude of this peak in the 3 studied samples.…”

“…Attempts to fit the second Se-Se coordination shell at about 3.63-3.70 ± 0.02 Å failed due to the small amplitude of this peak in the 3 studied samples. The bond distance of this shell would give insights on the crystalline Se, as was indicated by Eswayah et al 17 and Scheinost and Charlet. 42 Thus, due to the fact that EXAFS is a bulk technique, no strong structural evidence on the transformation of amorphous Se to trigonal Se was demonstrated, as it was suggested by STEM/HAADF analysis.…”

“…Se IV -free cultures (biotic) and Se IVamended media (abiotic) were used as controls. The gaseous samples were taken and analysed as described previously by Eswayah et al 17…”

“…Methylococcus capsulatus, Methylosinus trichosporium OB3b, Stenotrophomonas maltophilia, and Pseudomonas stutzeri NT-I have been shown to produce Se volatile species such as dimethyl selenide (DMSe) or dimethyl diselenide (DMDSe) as a consequence of a Se methylation process. [17][18][19] Several possible mechanisms for Se biomethylation have been proposed. Chasteen 20 suggested that methylation is preceded by the formation of Se 0 from Se IV , after which, Se 0 is reduced to a selenide form (H-Se-X) and subsequently methylated and converted to methane selenol and dimethyl selenide.…”

Green synthesis and biotransformation of amorphous Se nanospheres to trigonal 1D Se nanostructures: impact on Se mobility within the concept of radioactive waste disposal

“…13 Several studies have previously reported that bacteria can produce intracellular and extracellular amorphous Se (a-Se) nanospheres with a size ranging from 100 to 200 nm. 14,21 To a lesser extent, few studies have also described the formation of biogenic trigonal and monoclinic selenium (t-Se and m-Se). 8,22 Ho et al 23 reported the control of organic solvents like DMSO in the transformation of biogenic a-Se nanospheres to 1D t-Se nanostructures (e.g.…”