Isolation and characterization of a chromium‐reducing bacterium from a chromated copper arsenate‐contaminated site

Abstract

A Gram-negative bacterium (CRB5) was isolated from a chromium-contaminated site that was capable of reducing hexavalent chromium to an insoluble precipitate, thereby removing this toxic chromium species from solution. Analysis of the 16S rRNA from the isolate revealed that it was a pseudomonad with high similarity to Pseudomaonas synxantha. CRB5 was tolerant to high concentrations of chromate (500 mg l(-1)) and can reduce Cr(VI) under aerobic and anaerobic conditions. It also exhibited a broad range of reduction efficiencies under minimal nutrient conditions at temperatures between 4 degrees C and 37 degrees C and at pH levels from 4 to 9. As reduction increased, so did total cellular protein, indicating that cell growth was a requirement for reduction. Under low nutrient conditions with CRB5 or when using non-sterile contaminated groundwater from the site, reduction of Cr(VI) was followed by a increase in solution turbidity as a result of the formation of fine-grained Cr(III) precipitates, most probably chromium hydroxide mineral phases such as Cr(OH)3. Chromium adsorption and precipitation, as observed by transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (TEM/EDS), revealed that the surfaces of the cells were uniformly stained with bound Cr(III) and amorphous precipitates (as determined by selected area electron diffraction; SAED). A mass balance of chromium in a batch bioreactor revealed that up to 30% of the total Cr was as settable precipitates or bound to cells.

Reduction of Hexavalent Chromium by Viable Cells of Chromium Resistant Bacteria Isolated from Chromite Mining Environment

“…Arthrobacter sp. SUK 1201 cells reduced 100 M Cr(VI) in 48 h when the initial cell concentration was maintained at 10 9 cells/mL; however, with 10 fold increase in cell density, 100 M Cr(VI) was completely reduced in 30 h. Increase in cell density stimulated Cr(VI) reduction process (Table 2) as has been reported with Bacillus sphaericus AND 303 [28], Pseudomonas CRB5 [29], Ochrobactrum intermedium SDCr-5 [30], Lysinibacillus fusiformis ZC1 [25], and Arthrobacter sp. SUK 1205 [27].…”

Environmental Whole-Genome Amplification To Access Microbial Populations in Contaminated Sediments

“…However, we cannot exclude that the extremely small amount of DNA obtained from these samples biases the total number of predicted species. Both library 1 and library 3 contain sequences closely related to Pseudomonas synxantha, which is a known reducer of Cr(VI) as well as a hydrocarbon degrader, pointing toward a potential involvement in bioremediation (23,28,51). Overall, our data show that MDA can be used to obtain enough DNA from low-biomass samples to evaluate their microbial diversity.…”

Isolation and Characterization of Chromium(VI)-Reducing Bacteria from Tannery Effluents

“…Whole cells of IFR-2 and IFR-3 reduced 24 and 30% of the initial Cr(VI) concentration (1 mg/l) in 45 min respectively. Initial cell density has been shown to have a dramatic effect on Cr(VI) reduction [16]. A number of factors may be contributing to the observed trends, including Cr(VI) toxicity acclimation time needed to readjust cells to low nutrient loads before initiation of reduction.…”

“…Optimal Cr(VI) reduction was shown to be directly related to the optimum pH (8.0) for the growth of Bacillus isolates [4]. McLean et al [16] reported a wide range of pH between 6.0 to 9.0 for Cr(VI) reduction by P. synxantha.…”