Fe(III), Cr(VI), and Fe(III) mediated Cr(VI) reduction in alkaline media using a Halomonas isolate from Soap Lake, Washington

Abstract

Hexavalent chromium is one of the most widely distributed environmental contaminants. Given the carcinogenic and mutagenic consequences of Cr(VI) exposure, the release of Cr(VI) into the environment has long been a major concern. While many reports of microbial Cr(VI) reduction are in circulation, very few have demonstrated Cr(VI) reduction under alkaline conditions. Since Cr(VI) exhibits higher mobility in alkaline soils relative to pH neutral soils, and since Cr contamination of alkaline soils is associated with a number of industrial activities, microbial Cr(VI) reduction under alkaline conditions requires attention.Soda lakes are the most stable alkaline environments on earth, and contain a wide diversity of alkaliphilic organisms. In this study, a bacterial isolate belonging to the Halomonas genus was obtained from Soap Lake, a chemically stratified alkaline lake located in central Washington State. The ability of this isolate to reduce Cr(VI) and Fe(III) was assessed under alkaline (pH = 9), anoxic, non-growth conditions with acetate as an electron donor. Metal reduction rates were quantified using Monod kinetics. In addition, Cr(VI) reduction experiments were carried out in the presence of Fe(III) to evaluate the possible enhancement of Cr(VI) reduction rates through electron shuttling mechanisms. While Fe(III) reduction rates were slow compared to previously reported rates, Cr(VI) reduction rates fell within range of previously reported rates.

Bacterial Reduction of Cr(VI) and Fe(III) in In Vitro Conditions

“…A similar observation was also made for Cr(VI) reduction by B. subtilis, (Mangaiyarkaras, Vincenta, and Janarthanan 2011). Halomonas isolate was observed to reduce both Fe(III) and Cr(VI) in alkaline medium, as reported by VanEngelen et al (2008). However, pH 7 was found to be optimum for Cr(VI) reduction by Pseudomonas aeruginosa (Liu et al 2004).…”

“…The ability of several microbes (bacteria, fungi, microalgae) to reduce Cr(VI) to Cr(III) and Fe(III) to Fe (II) is of great interest in order to clean up soil/water environments polluted with chromate and iron (VanEngelen et al 2008). Reductions of Cr(VI) and Fe (III) have been reported in many bacterial genera, including Achromobacter, Arthrobacter, Bacillus, Corynebacterium, Microbacterium, Micrococcus, and Pseudomonas (Mclean and Beveridge 2001;VanEngelen et al 2008; Viti, Giovannetti, and Pace 2003;Tripathi et al 2011). In our study, we used the native bacteria isolated from fly ash, which might have acquired the ability to reduce Cr(VI) and Fe(III), as these metals are abundantly present in fly ash.…”

Biodegradation Potential of Halo(alkali)philic Prokaryotes

“…Less specific coreduction of the toxic oxyanions under aerobic conditions is commonly reported for moderately halophilic and haloalkaliphilic bacteria isolated from natural and industrial environments. Halo(alkali)philic Halomonas species can aerobically (unspecifically) reduce uranyles, selenate/selenite, chromate, and the radionuclide pertechnetate to a less toxic/soluble species at a salt concentration from 0.5 and up to 3.5 M and a pH from neutral to 10.5 (de Souza et al, 2001;Khijniak et al, 2003;Switzer Blum et al, 2001;van Engelen et al, 2008). A possibility for the detoxification of chlorate (ClO 4 − ) by its anaerobic reduction to Cl − has been shown only for moderate salt neutral conditions (up to 1.8 M NaCl) by a halophilic denitrifying mixed cultures (Logan et al, 2001;Okeke et al, 2002).…”

Structural characterization of amphiphilic siderophores produced by a soda lake isolate, Halomonas sp. SL01, reveals cysteine-, phenylalanine- and proline-containing head groups

“…In this report, we describe two distinct families of amphiphilic siderophores, both produced by an isolate from Soap Lake located in Washington State, Halomonas sp. SL01 (VanEngelen et al 2008). Soap Lake is a meromictic lake with a pH of 9.8 and a dissolved solid concentration ranging from 140 g/L in the monimolimnion layer to 14 g/L in the mixolimnion layer (Edmondson and Anderson 1965;Sorokin et al 2007).…”