Chromate resistant and reducing strains were isolated from chromium contaminated soil and identified as Bacillus sp. (KCH2 and KCH3), Leucobacter sp. (KCH4) and Exiguobacterium sp. (KCH5). KCH3 and KCH4 showed higher Cr(VI) tolerance (2 mM) and Cr(VI) reduction (1.5 mM) than KCH5 (1.5 mM and 0.75 mM, respectively). Cr(VI) reduction by CFEs of KCH3 and KCH4 showed NAD(P)H dependence, optimum activity at pH 5.5, low Km (45-55 μM) and substrate inhibition by Cr(VI) (&gt;75 μM), whereas that of KCH5 showed NADH dependence, pH optimum at 6.0, high Km (200 μM) and no inhibition by Cr(VI). Cr(VI) reduction was optimum at 35 °C for CFEs of KCH3 and KCH5 and 30 °C for that of KCH3. Cr(VI) reduction by CFEs of all the strains were inhibited by Hg2+ and enhanced by Cu2+. Activity enhancement by Cu2+ was more predominant (290%) for KCH4. The characterization of Cr(VI) reduction by CFEs of chromate resistant isolates of different genera is useful for development of Cr(VI) bioremediation. © 2007 Elsevier Ltd. All rights reserved.

Chandraraj Raj Krishnan

Department Of Biotechnology

Abhipsa Sarangi

Bacteria

bioremediation

Chromates

Chromium

contamination

pH effects

CHROMATE REDUCTASE

CHROMATE RESISTANT

Metal ions

chromic acid

reduced nicotinamide adenine dinucleotide phosphate

bacterium

CHROMATE

comparative study

IDENTIFICATION METHOD

inhibition

Microbial activity

reduction

SOIL MICROORGANISM

Soil pollution

article

Bacillus

EXIGUOBACTERIUM

in vitro study

LEUCOBACTER

nonhuman

priority journal

SOIL POLLUTANT

Biodegradation, Environmental

Drug Resistance, Microbial

Environmental pollution

Hydrogen-Ion Concentration

industrial waste

Ions

Kinetics

Microbial Sensitivity Tests

Oxidoreductases

phylogeny

RNA, Ribosomal, 16S

Soil Microbiology

SOIL POLLUTANTS

BACILLUS SP.

EXIGUOBACTERIUM SP.

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Bioresource Technology

Leucobacter sp. belongs to the metal stressed community and possesses higher tolerance to metals including chromium and can detoxify toxic hexavalent chromium by reduction to less toxic trivalent chromium. But, the mechanism of reduction of hexavalent chromium by Leucobacter sp. has not been studied. Understanding the enzyme catalyzing reduction of chromium is important to improve the species for application in bioremediation. Hence, a soluble reductase catalyzing the reduction of hexavalent chromium was purified from a Leucobacter sp. and characterized. The pure chromate reductase was obtained from the cell-free extract through hydrophobic interaction and gel filtration column chromatographic methods. It was a monomeric enzyme and showed similar molecular weights in both gel filtration (∼68KDa) and SDS-PAGE (64KDa). It reduced Cr(VI) using both NADH and NADPH as the electron donor, but exhibited higher activity with NADH. The optimal activity was found at pH 5.5 and 30°C. The Km and Vmax for Cr(VI) reduction with NADH were 46.57μM and 0.37μmolmin-1 (mg protein) -1, respectively. The activity was inhibited by p-hydroxy mercury benzoate, Ag2+ and Hg2+ indicating the role of thiol groups in the catalysis. The spectrophotometric analysis of the purified enzyme showed the absence of bound flavin in the enzyme. The N-terminal amino acid sequence and LC/MS analysis of trypsin digested purified enzyme showed similarity to dihydrolipoyl dehydrogenase. The purified enzyme had dihydrolipoyl dehydrogenase activity with dihydrolipoamide as the substrate, which suggested that Leucobacter sp. uses reductase with multiple substrate specificity for reduction of Cr(VI) detoxification. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Journal of Basic Microbiology

Detoxification of hexavalent chromium by Leucobacter sp. uses a reductase with specificity for dihydrolipoamide

Fulltext

African Journal of Microbiology Research

Hexavalent chromium reduction by metal resistant and halotolerant Planococcus maritimus VITP21

International Journal of Environmental Science and Technology

Remediation of chromium contaminants using bacteria

A Bacillus sp. RE was resistant to chromium and reduced Cr(VI) without accumulating chromium inside the cell. When Cr(VI) was 10 and 40 μg ml -1, &gt;95% of the total Cr(VI) was reduced in 24 and 72 h of growth, respectively, whereas at 80 μg Cr(VI) ml-1 only 50% of Cr(VI) was reduced. However growth was not affected; the cell mass was 0.7-0.8 mg ml -1 in all cases. The cell-free extract showed Cr(VI) reducing enzyme activity which was enhanced (&gt;5 fold) by NADH and NADPH. Like whole cells the enzyme also reduced Cr(VI) with decreasing efficiency on increasing Cr(VI) concentration. The enzyme activity was optimal at pH 6.0 and 30°C. The enzyme was stable up to 30°C and from pH 5.5 to 8, but from pH 4 to 5 the enzyme was severely destabilized. Its Km and Vmax were 14 μM and 3.8 nmol min-1 mg-1 respectively. The enzyme activity was enhanced by Cu2+ and Ni2+ and inhibited by Hg2+. © Springer 2006.

Biotechnology Letters

Reduction of Cr(VI) by a Bacillus sp.

Reduction of chromate by cell-free extract of Brucella sp. isolated from Cr(VI) contaminated sites

Reduction of toxic hexavalent chromium by Ochrobactrum intermedium strain SDCr-5 stimulated by heavy metals

Process Biochemistry

Cr(VI) reduction by Bacillus sp. isolated from chromium landfill

Extremophiles

Characterization of Exiguobacterium isolates from the Siberian permafrost. Description of Exiguobacterium sibiricum sp. nov.

Comparison of in vitro Cr(VI) reduction by CFEs of chromate resistant bacteria isolated from chromate contaminated soil

Journal	Bioresource Technology
ISSN	09608524
Open Access	No