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.

Chandraraj Raj Krishnan

Department Of Biotechnology

BACILLUS SP.

CHROMATE REDUCTASE

CHROMIUM TOLERANCE

CR(VI) BIOREMEDIATION

Copper

Enzyme kinetics

Nickel

pH effects

Sodium compounds

Chromium

article

Bacillus

bioremediation

cell proliferation

cell survival

culture technique

drug effect

metabolism

methodology

oxidation reduction reaction

physiology

Temperature

Biodegradation, Environmental

Cell Culture Techniques

Hydrogen-Ion Concentration

Oxidation-Reduction

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

Biotechnology Letters

In the present study, hexavalent chromium (Cr(VI)) reduction potential of chromium reductase associated with the cell-free extracts (CFE) of Arthrobacter rhombi-RE species was evaluated. Arthrobacter rhombi-RE, an efficient Cr(VI) reducing bacterium, was enriched and isolated from a chromium-contaminated site. Chromium reductase activity of Arthrobacter rhombi-RE strain was associated with the cell-free extract and the contribution of extracellular enzymes to Cr(VI) reduction was negligible. NADH enhanced the chromium reductase activity. The enzyme activity was optimal at a pH of 5.5 and a temperature of 30 °C. Among the ten electron donors screened, sodium pyruvate was the most effective one followed by NADH and propionic acid. Michaelis-Menten constant, K m, and maximum reaction rate, V max, obtained from the Lineweaver-Burk plot were 48 μM and 4.09 nM/mg protein/min, respectively, in presence of NADH as electron donor and 170.5 μM and 4.29 nM/mg protein/min, respectively, in presence of sodium pyruvate as electron donor. Ca2+ enhanced the enzyme activity while Hg2+, Cd2+, Ba 2+, and Zn2+ inhibited the enzyme activity. Among the various immobilization matrices screened, calcium alginate beads seemed to be the most effective one. Though immobilized enzyme system was able to reduce Cr(VI), the performance was not very encouraging in continuous mode of operation. © 2009 Humana Press.

Applied Biochemistry and Biotechnology

Hexavalent chromium reduction by free and immobilized cell-free extract of arthrobacter rhombi-RE

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.

Bioresource Technology

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

Arthrobacter sp. SUK 1201, a chromate resistant and reducing bacterium isolated from chromite mine overburden of Sukinda valley, Odisha, India has been evaluated for its hexavalent chromium [Cr(VI)] reduction potential using cell-free culture filtrate as extracellular chromate reductase enzyme. Production of the enzyme was enhanced in presence of Cr(VI) and its reducing efficiency was increased with increasing concentration of Cr(VI). The Michaelis-Menten constant (Km) and the maximum specific velocity (Vmax) of the extracellular Cr(VI) reductase were calculated to be 54.03 μM Cr(VI) and 5.803 U mg-1 of protein respectively showing high affinity towards Cr(VI). The reducing activity of the enzyme was maximum at pH 6.5-7.5 and at a temperature of 35 °C and was dependent on NADH. The enzyme was tolerant to different metals such as Mn(II), Mg(II) and Fe(III) and was able to reduce Cr(VI) present in chromite mine seepage. These findings suggest that the extracellular chromate reductase of Arthrobacter sp. SUK 1201 has a great promise for use in Cr(VI) detoxification under different environmental conditions, particularly in the mining waste water treatment systems. © 2016 Elsevier Ltd.

Chemosphere

Evaluation of chromate reductase activity in the cell-free culture filtrate of Arthrobacter sp. SUK 1201 isolated from chromite mine overburden

Indigenous isolates from the waters of chromite mining sites at Sukinda Valley, Orissa, India, showed a considerable enhancement in Cr (VI) bioreduction rate through adaptation and consortia development. On the basis of 16S-rRNA sequencing, these isolates were identified as Bacillus subtilis VITSUKMW1, Acinetobacter junii VITSUKMW2, and Escherichia coli VITSUKMW3. The native isolates showed a high tolerance at 500-1000 mg L-1 of Cr (VI). An increase in the reduction rate from 0.199-0.477 mg L-1 h-1 to 0.5-1.16 mg L-1 h-1 at 5-20 mg L -1 of initial Cr (VI) concentration was achieved by the adapted isolates. An increase in the growth rate and Cr (VI) reduction rate [0.86-2.6813 mg L-1 h-1 at 5-100 mg L-1 of initial Cr (VI) concentration] was observed in the ternary consortium of adapted isolates. The FT-IR spectra revealed the active participation of the bacterial surface groups in the reduction. The development of sequential processes (native → adapted → consortia) employing Cr (VI) tolerant isolates, proves to be a potential bioremediation strategy for specific chromite mine sites.

Industrial & Engineering Chemistry Research

Hexavalent Chromium Bioremoval through Adaptation and Consortia Development from Sukinda Chromite Mine Isolates

BIBECHANA

Thermodynamic properties of liquid InNa alloys

Biological Trace Element Research

Hexavalent Chromium Reduction by an Actinomycete, Arthrobacter crystallopoietes ES 32

Applied Microbiology and Biotechnology

In vitro reduction of hexavalent chromium by a cell-free extract of Bacillus sp. ES 29 stimulated by Cu 2+

Current Microbiology

Toxicity of Hexavalent Chromium and Its Reduction by Bacteria Isolated from Soil Contaminated with Tannery Waste

Chromate reduction and 16S rRNA identification of bacteria isolated from a Cr(VI)-contaminated site

Reduction of Cr(VI) by a Bacillus sp.

Journal	Biotechnology Letters
ISSN	01415492
Open Access	No