Microbial transformations of selenite by methane-oxidizing bacteria

Abdurrahman S Eswayah,Andreas C Scheinost,Philip H E Gardiner,Thomas J Smith,Nicole Hondow

doi:10.1007/s00253-017-8380-8

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 (SeO32−) but not selenate (SeO42−) 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.

Highlights

Despite its being one of the least abundant elements in the Earth’s crust, selenium is key to a number of critical biochemical reactions, and in addition to which selenium and its compounds have properties that lend themselves to many agricultural, industrial, medicinal and technological applications
After growth to OD600 of 0.5–0.8, was amended separately with selenate or selenite in order to test the ability of the two methanotrophic bacteria Ms trichosporium OB3b and Mc. capsulatus (Bath) to reduce both selenium oxyanions
This finding is in contrast to that of Lai et al (2016a), who used a biofilm microbial community in the presence of methane to show that selenate is reduced to elemental selenium

Summary

Introduction

Despite its being one of the least abundant elements in the Earth’s crust, selenium is key to a number of critical biochemical reactions, and in addition to which selenium and its compounds have properties that lend themselves to many agricultural, industrial, medicinal and technological applications. In Se-polluted environments, the element is mainly in the form of the water-soluble and toxic oxyanions, selenite (SeO32 −) and selenate (SeO42−) species. A variety of microorganisms are known to transform the different chemical forms of selenium, and play a key role in the recycling of this valuable element and in mitigating its toxicity. And technologically useful forms of selenium can be produced as a result of such microbial reactions, which include reduction, methylation, oxidation and demethylation. It appears that for most environmental microorganisms, dissimilatory reduction of the Se oxyanions and methylation of the products are the preferred microbial transformation pathways (Dungan and Frankenberger 1999; Eswayah et al 2016). Dissimilatory reduction of selenite to elemental selenium (Se0) has been demonstrated in a wide range of bacteria under aerobic and anaerobic conditions (Switzer Blum et al 1998; Switzer Blum et al 2001; Bebien et al 2001; Klonowska et al 2005), the potential contribution of aerobic methane-oxidizing bacteria, which are widespread in the environment, had not until recently been explored

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