Remediation of Chromium(VI) by a Methane-Oxidizing Bacterium

Abstract

Methane-oxidizing bacteria are ubiquitous in the environment and are globally important in oxidizing the potent greenhouse gas methane. It is also well recognized that they have wide potential for bioremediation of organic and chlorinated organic pollutants, thanks to the wide substrate ranges of the methane monooxygenase enzymes that they produce. Here we have demonstrated that the well characterized model methanotroph Methylococcus capsulatus (Bath) is able to bioremediate chromium(VI) pollution over a wide range of concentrations (1.4-1000 mg L(-1) of Cr(6+)), thus extending the bioremediation potential of this major group of microorganisms to include an important heavy-metal pollutant. The chromium(VI) reduction reaction was dependent on the availability of reducing equivalents from the growth substrate methane and was partially inhibited by the metabolic poison sodium azide. X-ray spectroscopy showed that the cell-associated chromium was predominantly in the +3 oxidation state and associated with cell- or medium-derived moieties that were most likely phosphate groups. The genome sequence of Mc. capsulatus (Bath) suggests at least five candidate genes for the chromium(VI) reductase activity in this organism.

Immobilization of Cr(VI) and Its Reduction to Cr(III) Phosphate by Granular Biofilms Comprising a Mixture of Microbes

“…Kemner et al (18) reported that the speciation of chromium associated with Pseudomonas fluorescens cells was consistent with association of Cr(III) with a phosphoryl functional group. A recent study showed reduction of Cr(VI) to Cr(III) by methane-oxidizing bacteria, a ubiquitous group of environmental bacteria (2). EXAFS analysis showed that Methylococcus capsulatus-associated chromium predominantly existed as Cr(III) and most likely associated with phosphate groups.…”

Methanotrophs: promising bacteria for environmental remediation

“…It has been suggested that methanotrophs also influence the speciation and bioavailability of metals in the environment (Choi et al 2006;Jenkins et al 1994). Hasin et al (2010) have reported the reductive transformation of soluble and more toxic Cr(VI) into a less toxic Cr(III)species by methanotrophic bacteria (Methylococcus capsulatus Bath), as the Cr(III) is insoluble and tends to get precipitated at high pH.…”

“…Therefore, mb might be particularly critical for ecological success of methanotrophs in such metal-polluted environments where proteins like methanobactin (mb) allow the selective acquisition of Cu, while protecting the methanotrophs against other similar potentially toxic metals. Microbial-based bioremediation of heavy metals, produced from metal plating, tanning, paper-making industries (Cervantes et al 2001;Hasin et al 2010;Zayed and Terry 2003), can be used for detoxification of metals through their conversion to less toxic and less soluble form like Cr(III). Hasin et al (2010) reported a well characterized model of methanotroph Methylococcus capsulatus (Bath), capable of bioremediation of chromium (VI) pollution over a wide range of concentrations (1.4-1,000 mg L -1 of Cr 6?…”

“…Methane (CH 4 ) is one of the greenhouse gases (GHGs), which contributes to global warming. Methane is about 23 times more effective as a greenhouse gas than carbon dioxide (CO 2 ) (Hasin et al 2010). Methanotrophs are the only known significant biological sink for atmospheric CH 4 and play a crucial role in reducing CH 4 load up to 15 % to the total global CH 4 destruction (Singh et al 2010).…”

“…Soils contaminated with heavy metals and/or organic pollutants are generally left abandoned for several years and therefore may not be safe for agricultural production. Recently, microbial bioremediation techniques have been found to alleviate the metal/ organic pollutant toxicity of contaminated soils (Hasin et al 2010;Shukla et al 2009). Methanotrophs may be promising bacteria for environmental bioremediation (Jiang et al 2010).…”