六价铬还原细菌Bacillus cereus S5.4的筛选鉴定及还原特性研究

六价铬生物毒性极大,是造成环境污染的主要重金属之一,其生物治理策略已引起了广泛关注。已经发现许多微生物具有六价铬抗性和还原性,但能工业应用的还十分有限。从宝钢电镀污泥中分离得到一系列高六价铬抗性菌株,其中一株S5.4显示出高六价铬还原性,经形态和生理生化特征及16s rDNA序列比对,鉴定为Bacillus cereus。该菌株好氧生长,在固体LB培养基上培养48h能耐受40mmol/L Cr6 ,并对Mn2 、Ba2 和Mo6 也显出高抗性;在液体LB培养基中培养72h完全还原2mmol/L Cr6 ,并能在补充培养基和六价铬的条件下连续还原。该菌株还原六价铬时,最适浓度为2mmol/L Cr6 ,最适温度范围30~37℃,最适pH 7~9。     

Removal of hexavalent chromium using distillery sludge

Batch mode experiments were conducted to study the removal of hexavalent chromium from aqueous and industrial effluent using distillery sludge. Effects of pH, contact time, initial concentration and adsorbent dosage on the adsorption of Cr(VI) were studied. The data obeyed Langmuir and Freundlich adsorption isotherms. The Langmuir adsorption capacity was found to be 5.7 mg/g. Freundlich constants K(f) and n were 2.05 [mg/g(L/mg)(n)] and 3.9, respectively. Desorption studies indicated the removal of 82% of the hexavalent chromium. The efficiency of adsorbent towards the removal of chromium was also tested using chromium-plating wastewater.     

Removal of chromium and pentachlorophenol from tannery effluents

Three bacterial strains, including one Acinetobacter sp. PCP3, grown in the presence of minimal salt medium and pentachlorophenol (PCP) as sole carbon source in the chemostat showed higher utilization of PCP and adsorption of chromium. In sequential bioreactor, tannery effluents treated initially by bacterial consortium followed by fungus removed 90% and 67% chromium and PCP respectively, whereas in another set of bioreactor in which effluents was treated initially by fungi followed by bacteria could remove 64.7% and 58% chromium and PCP, respectively.     

Isolation and characterization of a highly effective bacterium Bacillus cereus b-525k for hexavalent chromium detoxification

The chromate resistant Gram-positive Bacillus cereus strain b-525k was isolated from tannery effluents, demonstrating optimal propagation at 37 °C and pH 8. The minimum inhibitory concentration (MIC) test showed that B. cereus b-525k can tolerate up to 32 mM Cr⁶⁺, and also exhibit the ability to resist other toxic metal ions including Pb²⁺ (23 mM), As³⁺ (21 mM), Zn²⁺ (17 mM), Cd²⁺ (5 mM), Cu²⁺ (2 mM), and Ni²⁺ (3 mM) with the resistance order as Cr ⁶⁺ > Pb²⁺ > As³⁺ >Zn²⁺ >Cd²⁺ >Ni²⁺ >Cu²⁺. B. cereus b-525k showed maximum biosorption efficiency (q) of 51 mM Cr⁶⁺/g after 6 days. Chromate stress elicited pronounced production of antioxidant enzymes such as catalase (CAT) 191%, glutathione transferase (GST) 192%, superoxide dismutase (SOD) 161%, peroxidase (POX) 199%, and ascorbate peroxidase (APOX) (154%). Within B. cereus b-525k, the influence of Cr⁶⁺ stress (2 mM) did stimulate rise in levels of GSH (907%) and non-protein thiols (541%) was measured as compared to the control (without any Cr⁶⁺ stress) which markedly nullifies Cr⁶⁺ generated oxidative stress. The pilot scale experiments utilizing original tannery effluent showed that B. cereus b-525k could remove 99% Cr⁶⁺ in 6 days, thus, it could be a potential candidate to reclaim the chromate contaminated sites.     

Bioremediation of hexavalent chromium from wastewater using bacteria-a green technology

Biodegradation - Hexavalent chromium has high toxic effect on the ecological system. The aim of the present study is to isolate and characterize the bacteria that can reduce the toxicity of...     

Modeling hexavalent chromium removal in a Bacillus sp. fixed-film bioreactor

A one-dimensional diffusion-reaction model was developed to simulate Cr(VI) reduction in a Bacillus sp. pure culture biofilm reactor with glucose as a sole supplied carbon and energy source. Substrate utilization and Cr(VI) reduction in the biofilm was best represented by a system of (second-order) partial differential equations (PDEs). The PDE system was solved by the (fourth-order) Runge-Kutta method adjusted for mass transport resistance using the (second-order) Crank-Nicholson and Backward Euler finite difference methods. A heuristic procedure (genetic search algorithm) was used to find global optimum values of Cr(VI) reduction and substrate utilization rate kinetic parameters. The fixed-film bioreactor system yielded higher values of the maximum specific Cr(VI) reduction rate coefficient and Cr(VI) reduction capacity (kmc = 0.062 1/h, and Rc = 0.13 mg/mg, respectively) than previously determined in batch reactors (kmc = 0.022 1/h and Rc = 0.012 mg/mg). The model predicted effluent Cr(VI) concentration well with 98.9% confidence (sigmay2 = 2.37 mg2/L2, N = 119) and effluent glucose with 96.4 % confidence (sigmay(w)2 = 5402 mg2/L2, N = 121, w = 100) over a wide range of Cr(VI) loadings (10-498 mg Cr(VI)/L/d).     

Alleviation of toxic hexavalent chromium using indigenous aerobic bacteria isolated from contaminated tannery industry sites

In the last decade, much attention has been paid to bioremediation of Cr(VI) using various bacterial species. Cr(VI) remediation by indegeneous bacteria isolated from contaminated sites of a tannery industry located in Tamil Nadu, India, was investigated in this study. Three Cr(VI) resistant bacterial strains (TES-1, TEf-1, and TES-2) were isolated and selected based on their Cr(VI) reduction ability in minimal salt medium. Among these three bacterial strains, TES-1 was found to be most efficient in bioreduction, while TES-2 was only found to be Cr(VI) resistant and showed negligible bioreduction, whereas TEf-1 was observed to be most Cr(VI) tolerant. Potential for bioremediation of TES-1 and TEf-1 was further investigated at different concentrations of Cr(VI) in the range of 50 to 350 mg L^?1. TEf-1 showed prominent synchronous growth throughout the experiment, whereas TES-1 took a longer acclimatization time. Minimum inhibitory concentrations (MIC) of Cr(VI) for TES-1 and TEf-1 were approximated as 600 mg L^?1 and 750 mg L^?1, respectively. The kinetic behavior of Cr(VI) reduction by TES-1 and TEf-1 exhibited zero- and first-order removal kinetics for Cr(VI), respectively. The most efficient strain TES-1 was identified as Streptomyces sp. by gene sequencing of 16S rRNA.     

Removal of hexavalent chromium using a novel cross linked xanthated chitosan

Suitability of a novel cross linked, chemically modified chitosan as highly efficient adsorbent for the recovery of toxic chromium(VI) was studied. After cross linking with glutaraldehyde, xanthate group was grafted onto the back bone of chitosan. Sorption was found to be both pH and concentration dependent, with pH 3 being the optimum value. Both, chemically modified beads (CMCB) and flakes (CMCF) followed a pseudo-second-order kinetics with a rate constant of 2.037 and 4.639 g/mg/min, respectively. The equilibrium data followed the Langmuir isotherm model with maximum capacities of 625 mg/g and 256.4 mg/g and for CMCF and CMCB respectively. Desorption studies revealed the reusability of the sorbent for at least 10 cycles without any significant change in adsorption capacities.     

A novel technology for biosorption and recovery hexavalent chromium in wastewater by bio-functional magnetic beads

The goal of this study was to develop an applied technique for the removal and recovery of heavy metal in wastewater. It is novel that the Cr(VI) could be adsorbed and recovered by bio-functional magnetic beads. Furthermore, the magnetic separation technology would make their separation more convenient. The beads were constituted by the powder of Rhizopus cohnii and Fe(3)O(4) particles coated with alginate and polyvinyl alcohol (PVA). The parameters effecting Cr(VI) removal were obtained: the optimum pH 1.0 and optimum temperature 28 degrees C. The biosorption took place mainly in form of Cr(VI) and R. cohnii biomass played a key role in Cr(VI) adsorption. The model of Langmuir isotherm and Lagergren could be better used to fit the sorption process and kinetics, respectively. The beads still maintained predominant characteristics of adsorption, recovery and magnetism after five cycles for adsorption-desorption. The mechanism of adsorption was gained by Fourier transform infrared spectroscopy (FTIR), raman spectroscopy (RS) and scanning electron microscopy (SEM). The groups of -NH(3)(+), -NH(2)(+)-, and NH- played an important role in the Cr(VI) adsorption. Consequently, the beads exhibited the superior performances in Cr(VI) cleanup, separation and recovery and the perspective potential in application.     

Efficiency of Penicillium chrysogenum PTCC 5037 in reducing low concentration of chromium hexavalent in a chromium electroplating plant wastewater

The effectiveness of Penicillium chrysogenum was evaluated for reducing Cr(VI) from the wastewater of a chromium electroplating plant. Statistically-based experimental designs were applied to optimize the condition for reducing Cr(VI) to Cr(III). By applying Plackett-Burman factorial design and central composite design as the optimization step, attempts were made to identify optimal values of the three factors that bringing about maximum microorganism activity and therefore maximum hexavalent chromium(VI) bioreduction. It was found that each gram of P. chrysogenum of dry biomass condition could reduce 66 mg of Cr(VI) to Cr(III) in the wastewater of the chromium electroplating plant.     

Genetic correlation between chromium resistance and reduction in Bacillus brevis isolated from tannery effluent

Aims:  To investigate the genetic basis of Cr(VI) resistance and its reduction to Cr(III) in indigenous bacteria isolated from tannery effluent.
Methods and Results:  Four bacteria resistant to high Cr(VI) levels were isolated and identified as Bacillus spp. Their Cr(VI) reduction ability was tested. To assess the genetic basis of Cr(VI) resistance and reduction, plasmid transfer and curing studies were performed. Among all, B. brevis was resistant to 180 μg Cr(VI) ml⁻¹ and showed the greatest degree of Cr(VI) reduction (75·8%) within 28 h and its transformant was resistant to 160 μg Cr(VI) ml⁻¹ and reduced 69·9% chromate. It harboured a stable 18 kb plasmid DNA. Transfer and curing studies revealed that both the chromate resistance and reduction were plasmid mediated. The presence of other metal cations did not have any significant effect on Cr(VI) bioreduction.
Conclusions:  Bacillus brevis was resistant to elevated Cr(VI) levels and may potentially reduce it in short time from an environment where other metal ions are also present in addition to chromium ions. The strain tested shows a positive correlation between genetic basis of Cr(VI) resistance and reduction.
Significance and Impact of the Study:  To our knowledge, this is the first study on the genetic correlation between chromium resistance and reduction in bacteria. Such strains may potentially be useful in biotechnological applications and in situ Cr(VI) bioremediation.     

Hexavalent chromium reduction by bacteria from tannery effluent

Chromium is generated from several industrial processes. It occurs in different oxidation states, but Cr(III) and Cr(VI) are the most common ones. Cr(VI) is a toxic, soluble environmental contaminant. Some bacteria are able to reduce hexavalent chromium to the insoluble and less toxic Cr(III), and thus chromate bioremediation is of considerable interest. An indigenous chromium-reducing bacterial strain, Rb-2, isolated from a tannery water sample, was identified as Ochrobactrum intermedium, on the basis of 16S rRNA gene sequencing. The influence of factors like temperature of incubation, initial concentration of Cr, mobility of bacteria, and different carbon sources were studied to test the ability of the bacterium to reduce Cr(VI) under variable environmental conditions. The ability of the bacterial strain to reduce hexavalent chromium in artificial and industrial sewage water was evaluated. It was observed that the mechanism of resistance to metal was not due to the change in the permeability barrier of the cell membrane, and the enzyme activity was found to be inductive. Intracellular reduction of Cr(VI) was proven by reductase assay using cell-free extract. Scanning electron microscopy revealed chromium precipitates on bacterial cell surfaces, and transmission electron microscopy showed the outer as well as inner distribution of Cr(VI). This bacterial strain can be useful for Cr(VI) detoxification under a wide range of environmental conditions.     

Cytogenetic effects of hexavalent chromium in Bulgarian chromium platers

The aim of the present study was to evaluate the genotoxic effects of hexavalent chromium (Cr(VI)) in vivo in exposed Bulgarian chromium platers by using classical cytogenetic and molecular cytogenetic analyses of peripheral lymphocytes and exfoliated buccal cells. No significant difference was observed between the exposed workers and the controls with regard to the frequency of cells with chromosome aberrations (CAs) using conventional Giemsa staining and in the frequency of sister chromatid exchanges (SCEs). However, there was a significant increase in the number of cells with micronuclei (MN) in peripheral lymphocytes from chromium exposed workers as compared to the controls. In the buccal cells from these workers, this increase was even more pronounced. Cytosine arabinoside (AraC), an inhibitor of DNA synthesis and repair, was found to significantly increase the levels of MN in vitro in the lymphocytes of both groups. The increase was more expressed in the lymphocytes of chromium exposed workers. Both centromere positive (C(+)) as well as centromere negative (C(-)) MN were observed by the fluorescence in situ hybridization (FISH) technique in both of the cell types studied. No difference between C(+) and C(-) MN frequencies was found in the lymphocytes as well as in the buccal cells. Thus, Cr(VI) appears to have both clastogenic as well as aneugenic effects in humans.     

Bacterial reduction of hexavalent chromium

Summary Cr(VI)-reducing bacteria are widespread and Cr(VI) reduction occurs under both aerobic and anaerobic conditions. Under aerobic conditions, both NADH and endogenous cell reserves may serve as the electron donor for Cr(VI) reduction. Under anaerobic conditions, electron transport systems containing cytochromes appear to be involved in Cr(VI) reduction. High cell densities are necessary to obtain a significant rate of Cr(VI) reduction. Cr(VI) reduction by bacteria may be inhibited by Cr(VI), oxygen, heavy metals, and phenolic compounds. The optimum pH and temperature observed for Cr(VI) reduction generally coincide with the optimal growth conditions of cells. The optimum redox potential for Cr(VI) reduction has not yet been established.     

Low-cost supports used to immobilize fungi and reliable technique for removal hexavalent chromium in wastewater

The main goal of this study was to exploit low-cost and efficient sorbents for the removal and recovery of Cr(VI) in wastewater. Three supports of sawdust, polyurethane and alginate were applied to immobilize living and dead R. cohnii cells, respectively. There was a distinct increase in the Cr(VI) removal efficiency before and after the HCl-pretreatment. Langmuir adsorption isotherm model was well used to describe the distribution of Cr(VI) between the liquid and solid phases in batch studies. The values of q0 predicted by Thomas model were near to experimental ones in the experiments of packed column. The breakthrough curves calculated with this model were consistent well with experimental ones at a largely extent. Desorption, regeneration and reuse of the packed column were studied. After 5 cycles, adsorption capacity was still kept at higher level, reaching to 91.4, 87.9, 91.4 and 93.3mg/l contrasted with the first cycle (94.1, 90.4, 94.8 and 98.5mg/l) and the desorption efficiency were 85.0%, 96.2%, 93.4% and 91.4% compared with the first cycle (87.6%, 95.4%, 96.7% and 94.3%), corresponding to living cells immobilized with sawdust, polyurethane, and dead cells immobilized with polyurethane and alginate, respectively. The results indicated that the packed columns with the immobilized living and dead R. cohnii cells were the better option to adsorb, desorb and recover Cr(VI) from wastewater.     

真菌还原Cr（VI）的研究

从不同来源的样品中分离筛选出几株抗Ｃｒ（ＶＩ）的真菌,他们能在含３００￣５００ｍｇ／ＬＫ２Ｃｒ２Ｏ７的蔗糖合成培养基中生长,其中ＢＳ－１菌株抗Ｋ２Ｃｒ２Ｏ７达９００ｍｇ／Ｌ．ＢＳ－１等４株真菌在含２００ｍｇ／Ｌ Ｋ２Ｃｒ２Ｏ７的培养基中生长４￣６ｄ后,培养液中的Ｃｒ（ＶＩ）已全部消失。这些真菌经鉴定为青霉菌ＢＳ－１和ＢＳ－３,黑曲霉ＢＲ－４和黄曲霉ＢＸ－１。经紫外可见光扫描及化学分析证实,高毒的Ｃ     

Bioremediation of hexavalent chromium in soil microcosms

Pseudomonas mendocina when added in soil microcosms could immobilize 100 g (2 mM) chromate/g soil in 8 h by converting it into trivalent form. The chromate-contaminated soils, after microbiological treatment, supported growth of wheat seedlings without exerting any toxic effects. The method is potentially useful in the bioremediation of chromate-contaminated sites. © Rapid Science Ltd. 1998