Okeke Benedict C, Laymon Jeffery, Crenshaw Shakena, Oji Charles
Department of Biology, Auburn University Montgomery, P.0. Box 244023, Montgomery, AL, 36124, USA.
Biol Trace Elem Res. 2008 Summer;123(1-3):229-41. doi: 10.1007/s12011-008-8098-7. Epub 2008 Mar 4.
Hexavalent chromium, Cr(VI), is toxic to living systems. Widespread contamination of water and soil by Cr(VI) present a serious public health problem. Chromium-resistant bacteria can reduce and detoxify Cr(VI). Twelve bacteria resistant to high concentrations of Cr(VI) were isolated from soil enrichment cultures. Environmental parameters and kinetic parameters of Cr(VI) bioreduction by one monoculture isolate, identified by 16S rRNA gene sequence as Bacillus sp. PB2, were studied. The optimal temperature for growth and Cr(VI) reduction was 35 degrees C. The isolate grew luxuriantly and substantially reduced Cr(VI) at initial pH 7.5 to 9. Maximal Cr(VI) bioreduction occurred at initial pH 8.0. Substantial Cr(VI) bioreduction was observed in salt media, but removal efficiency was inversely related to salt concentration (1-9%). Michaelis-Menten hyperbolic equation and the Lineweaver-Burk double reciprocal plot were comparatively employed to determine the k (m) and V (max) of Cr(VI) bioreduction. A k (m) of 82.5 microg mL(-1) and V (max) of 7.78 microg mL(-1) h(-1) were calculated by nonlinear regression analysis of the hyperbola curve. Linear regression analysis of the double reciprocal plot revealed k (m) and V (max) of 80.9 microg mL(-1) and 10.6 microg mL(-1) h(-1), respectively. Time course studies displayed about 90% reduction of Cr(VI) at an initial concentration of 8,000 microg L(-1) in 8 h, with an estimated t (1/2) of 4 h. Data from time course analysis of the rate of Cr(VI) bioreduction fitted zero-order model, and the kinetic constant k was calculated to be 840 microg L(-1) h(-1). The monoculture isolate, Bacillus sp. PB2, strongly reduces Cr(VI) and could be used for bioremediation of Cr(VI)-contaminated aquatic and terrestrial environments.
六价铬（Cr(VI)）对生物系统有毒。Cr(VI)对水和土壤的广泛污染构成了严重的公共卫生问题。耐铬细菌可以还原Cr(VI)并使其解毒。从土壤富集培养物中分离出12株对高浓度Cr(VI)具有抗性的细菌。对其中一株通过16S rRNA基因序列鉴定为芽孢杆菌属PB2的纯培养菌株进行Cr(VI)生物还原的环境参数和动力学参数研究。生长和Cr(VI)还原的最适温度为35℃。该菌株在初始pH值为7.5至9时生长旺盛并能大量还原Cr(VI)。在初始pH值为8.0时发生最大的Cr(VI)生物还原。在盐培养基中观察到大量的Cr(VI)生物还原，但去除效率与盐浓度（1 - 9%）呈负相关。采用米氏双曲线方程和Lineweaver - Burk双倒数图来确定Cr(VI)生物还原的k(m)和V(max)。通过对双曲线曲线的非线性回归分析计算出k(m)为82.5μg mL(-1)，V(max)为7.78μg mL(-1) h(-1)。双倒数图的线性回归分析显示k(m)和V(max)分别为80.9μg mL(-1)和10.6μg mL(-1) h(-1)。时间进程研究表明，在初始浓度为8000μg L(-1)时，8小时内Cr(VI)的还原率约为90%，估计半衰期（t(1/2)）为4小时。Cr(VI)生物还原速率的时间进程分析数据符合零级模型，动力学常数k计算为840μg L(-1) h(-1)。纯培养菌株芽孢杆菌属PB2能强烈还原Cr(VI)，可用于Cr(VI)污染的水生和陆地环境的生物修复。
