Biological removal of toxic chromium using an Enterobacter cloacae strain that reduces chromate under anaerobic conditions

Abstract

Hexavalent chromium (chromate: CrO.+-) is toxic and mutagenic for most organisms.'.* In humans, chromate causes irritation and corrosion of skin and respiratory tract, and is believed to be responsible for lung carcinoma. Chromate is also hazardous to fauna and flora in natural aquatic ecosyst e m~.~ Wastewaters containing toxic chromate are generated in many industrial processes including chrome leather tanning, chromium plating, metal cleaning and processing, wood preservation, and alloy p r e p a r a t i~n .~ These wastewaters must be treated before discharged to natural environments. Recently, we have isolated a chromate-reducing bacterium, identified as Enterobacter cloacae, which is resistant to high levels of chromate (10 mM) under both aerobic and anaerobic conditions.6 During anaerobic growth, the E. cloacar isolate reduces chromate to trivalent chromium (Cr3') which is subsequently precipitated in the culture medium. Trivalent chromium is much less toxic than chromate. I Therefore, the ability of this bacterium to reduce chromate may be useful not only for detoxification, but also for removal of toxic chromium from wastewaters.Since there are no reports on the biological removal of aqueous chromium species, excepting simple microbial ads~r p t i o n ,~ the present communication demonstrates the potential of the E. cloacae chromate-reducing strain to remove toxic chromate from wastewaters. MATERIALS AND METHODS Bacterial StrainEnterobacter cloacae strain HO 1 was isolated from an activated sludge sample from a municipal wastewater treatment plant. The characteristics of E . cloacae H 0 1 have been previously described.6

Simultaneous Cellulose Degradation and Electricity Production by Enterobacter cloacae in a Microbial Fuel Cell

“…These findings reinforce the need to identify important electricity-generating bacteria in MFCs by using techniques that isolate bacteria based on their ability to generate current and not just their dissimilatory iron reduction ability. Although E. cloacae could not reduce Fe(III), it has been reported that this strain can reduce soluble chromate ion to Cr(III) and selenate to selenium (16,17).…”

Modulation of tolerance to Cr(VI) and Cr(VI) reduction by sulfate ion in a Candida yeast strain isolated from tannery wastewater

“…Philip et al [50] reported that the presence of up to 1,000 mg/L (10.4 mM) of sulfate did not affect Cr(VI) reduction by Bacillus coagulans. However, Cr(VI) reduction by Enterobacter cloacae HO1 under anaerobic conditions showed 32% inhibition in the presence of only 25 lM of sulfate [26].…”

Effect of complexing agents on reduction of Cr(VI) by Desulfovibrio vulgaris ATCC 29579

“…that reduce Cr(VI) are P. ambigua C-13 and P.¯uorescens LB300, the latter aerobically and anaerobically (Bopp and Ehrlich, 1988). Among enterobacterial strains, Enterobacter aerogenes EAO reduced Cr(VI) in rich medium, with chromate reductase activity induced by nitrite (Clark, 1994), whereas E. cloacae HO1 reduced up to 2 mM CrO 4 2) to Cr(III), which was precipitated in the culture medium as Cr(OH) 3 anaerobically (Komori et al, 1990) at pH 7.0 to 7.8 (De Mel et al, 1994). In contrast, Escherichia coli ATCC 33456 reduced Cr(VI) aerobically and anaerobically within 12 h (Shen and Wang, 1993), but the product of the reaction [probably Cr(III)] was almost completely (98%) retained in a soluble form in the culture supernatant (Shen and Wang, 1993).…”