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. 2011 Apr;18(2):157-67.
doi: 10.1016/j.sjbs.2010.12.003. Epub 2010 Dec 17.

Bioreduction of Cr(VI) by alkaliphilic Bacillus subtilis and interaction of the membrane groups

M S Mary Mangaiyarkarasi  1 , S Vincent, S Janarthanan, T Subba Rao, B V R Tata
Affiliations

Bioreduction of Cr(VI) by alkaliphilic Bacillus subtilis and interaction of the membrane groups

M S Mary Mangaiyarkarasi et al. Saudi J Biol Sci. 2011 Apr.

Abstract

Detoxification of Cr(VI) under alkaline pH requires attention due to the alkaline nature of many effluents. An alkaliphilic gram-positive Bacillus subtilis isolated from tannery effluent contaminated soil was found to grow and reduce Cr(VI) up to 100% at an alkaline pH 9. Decrease in pH to acidic range with growth of the bacterium signified the role played by metabolites (organic acids) in chromium resistance and reduction mechanism. The XPS and FT-IR spectra confirmed the reduction of Cr(VI) by bacteria into +3 oxidation state. Chromate reductase assay indicated that the reduction was mediated by constitutive membrane bound enzymes. The kinetics of Cr(VI) reduction activity derived using the monod equation proved (K s = 0.00032) high affinity of the organism to the metal. This study thus helped to localize the reduction activity at subcellular level in a chromium resistant alkaliphilic Bacillus sp.

Keywords: 16S rRNA identification; Bacillus sp.; Chromate reductase; Cr(VI) reduction; Membrane bound proteins.

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Figures

Figure 1
Figure 1
Phylogenetic tree based on 16S rRNA gene sequence: shows the relationship between members of family Bacillaceae and G7 (test organism). The bar represents distance values calculated in MEGA and values at nod represent percentage of 1000 bootstrap replicates. Numbers in bracket represent Genbank accession numbers.
Figure 2
Figure 2
Reduction of Cr(VI) at different pH.
Figure 3
Figure 3
Cr(VI) reduction vs. growth over a period of time (in mg/L) (A) 50; (B) 100; (C) 150; (D) 200.
Figure 4
Figure 4
(A) EDX spectrum of the Bacillus cells shows presence of chromium on the cell surface. Inset: SEM images of Bacillus cells.
Figure 5
Figure 5
XPS spectrum of cells shows presence of chromium in +3 oxidation state.
Figure 6
Figure 6
(a) FT-IR spectra of the cells unexposed and exposed to Cr(VI). (b) Spectra showing the peak–functional group assignment and comparison of peak area.
Figure 7
Figure 7
Reduction of pH and chromium at different initial Cr(VI) concentrations (in mg/L) (A) 50; (B) 100; (C) 150; (D) 200.
See this image and copyright information in PMC

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