Chromium Reducing Bacteria Research Articles

Bioremediation of Hexavalent Chromium By Bacteria Isolated From Buriganga River, Dhaka City

Environmental pollution due to hexavalent chromium (Cr6+) is widespread because of the anthropogenic activities in various industrial processes, notably in leather tanning. Hexavalent chromium (Cr6+) is considered as highly toxic, carcinogenic, and mutagenic due to its high solubility in water, interaction with cellular proteins, and biological membrane permeability. Trivalent chromium (Cr3+), on the other hand, is less water-soluble, and relatively benign in nature. Thus, bioreduction of toxic Cr6+ to relatively non-toxic Cr3+ by microorganisms can be an inexpensive and eco-friendly option for chromium bioremediation. In this regard, the present study attempted to isolate chromium-reducing bacteria from Buriganga River in order to assess their capability for chromium bioremediation. Ten chromium-tolerating bacterial isolates were successfully identified. The results revealed that these isolates, particularly strains of Bacillus subtilis, exhibited a remarkable ability to remove up to 89% of hexavalent chromium from the contaminated medium within three days of incubation.
 Stamford Journal of Microbiology, 2023. Vol. 13, Issue 1, p. 25-29

Cr(VI) removal from wastewater using nano zero-valent iron and chromium-reducing bacteria.

Significant global efforts are currently underway to alleviate the presence of toxic metals in water bodies, aiming to encourage a sustainable environment. Nevertheless, the scientific community has yet to methodically inspect the performance and mechanisms underlying the interaction between nanomaterials and microorganisms in this context. Therefore, this study seeks to address this knowledge gap by developing a novel system that integrates nano zero-valent iron (nZVI) with chromium-reducing bacteria (CrRB) to efficiently remove Cr(VI) from water sources. The combined use of RBC600 and CrRB resulted in a Cr(VI) removal rate of 77.73%, displaying a substantial improvement of 17.61% compared to the use of CrRB alone. The efficacy of Cr(VI) elimination was observed to be affected by several factors within the system, such as the pH value, the quantity of nZVI added, the degree of CrRB inoculation, and the initial concentration of Cr(VI) at the onset of the experiment. When the pH was adjusted to 5, the complete removal of 200 mg/L Cr(VI) was achieved within 36 h. Increasing the dosage of nZVI to above 2 g/L resulted in the complete elimination of Cr(VI) from the solution within 72 h. This can be attributed to the availability of more reaction sites for the reduction of Cr(VI), facilitated by the higher nZVI dose. Additionally, the increased dose of nZVI allowed for the dissolution of more reactive Fe(II) ions. The characterization analysis, high-throughput sequencing, and fluorescence quantitative PCR results have established that CrRB and its extracellular polymer effectively reduce and complex Cr(VI). This process facilitated the dissolution of the passivated layer on the surface of nZVI, thus significantly enhancing the efficiency of nZVI in responding to Cr(VI). Additionally, the presence of nZVI created a favorable living environment for CrRB, resulting in increased richness and diversity within the CrRB community. These findings provide valuable preliminary insights into the mechanism underlying Cr(VI) elimination by the synergistic interaction between nZVI and CrRB. Therefore, this study establishes a solid theoretical foundations for the application of nano-bio synergy in the remediation of Cr(VI).

Diversity of hexavalent chromium-reducing bacteria and physicochemical properties of the Kanpur tannery wastewater

The tannery effluent sample was collected from a tannery located in Jajmau area of Kanpur, India and subjected to physicochemical analysis. The tannery effluent was brownish in color with a foul odor. It was alkaline in nature and characterized by high biological oxygen demand (BOD), chemical oxygen demand (COD), total solids (TS), total dissolved solids (TDS) and high amounts of chromium. Total eighteen chromium resistant bacteria were isolated from the tannery effluent sample. Based on the 16S rRNA gene sequencing and phylogenetic analysis, these eighteen bacteria belong to seven different genera including Bacillus, Pseudomonas, Kocuria, Cellulosimicrbium, Klebsiella, Microbacterium, Brucella. The members of genus Bacillus constitute 28% of total chromium transforming isolates; followed by members of genus Microbacterium (17%) Brucella (17%), Pseudomonas (11%), Cellulosimicrobium (11%), Kocuria (11%) and Klebsiella (5%). Furthermore, all eighteen bacteria were screened for their ability to reduce hexavalent chromium with increasing concentrations (600–1200 ppm) of potassium dichromate. Results showed that one bacterium, Bacillus licheniformis strain KNP exhibited hexavalent chromium reduction up to concentrations of 1000 ppm. This bacterium was selected for further study.

Screening of Chromium-reducing Bacteria from Tannery Effluents

Tannery effluent has remained one of the major sources of chromium pollution in the environment. Although conventional methods have been widely used, they are inefficient and costly. Bacterial remediation is one of the best alternatives being proposed. Therefore, the aim of this research was to isolate bacteria from tannery effluents and screen them for chromium-reduction potentials. Three different tannery effluents were collected and used for the isolation of chromium-reducing bacteria. The organisms were identified using morphological and biochemical characteristics and screened on 1% (v/v) Cr (VI). The results revealed the presence of three bacterial species, namely: Bacillus subtilis, Escherichia coli and Pseudomonas sp. The screening results revealed that out of the three bacterial isolates, Bacillus subtilis had the highest reduction potential (86.23%), while equal reduction capacity was recorded in both E. coli and Pseudomonas sp. (84.03%). Therefore, these three isolates can be used as a consortium to improve biological remediation of Cr (VI) effluents.

Bioremediation of hexavalent chromium by transformation of Escherichia coli DH5α with chromate reductase (ChrR) genes of Pseudomonas putida isolated from tannery effluent.

Hexavalent chromium Cr(VI), a toxic heavy metal, is a serious pollutant of tannery effluent, and its accumulation in soil and water causes severe environmental concerns of increasing public health issues. The present study focus on the isolation and identification of chromium-reducing bacteria collected from the tannery industry in Dindigul, Tamil Nadu. Chromium-reducing bacteria Pseudomonas putida were identified by 16S rRNA sequencing followed by BLAST search. The plasmid with Cr(VI) reductase gene was isolated from Pseudomonas putida and transferred to E. coli DH5α for further studies. The bacterial cultures were kept under controlled conditions for 72h to observe the growth rates and bacterial resistance to chromium. When strains wild type and transformant E. coli DH5α were grown in chromium supplemented media revealed significant growth, but strains cured type Pseudomonas putida and E. coli DH5α were minimum growth. The Cr(VI) reduction employed by transformant E. coli DH5α and wild Pseudomonas putida was 42.52±1.48% and 44.46±0.55%, respectively. The culture supernatant of the wild Pseudomonas putida and transformant E. coli DH5α showed an increased reduction of Cr(VI) compared to cell extract supernatant and cell debris due to the extracellular activity of chromium reductase has been responsible for Cr(VI) reduction. Besides, the chromium reductase gene was confirmed in the isolated Pseudomonas putida and transformant E. coli DH5α. Transformant bacteria could employ an alternative method for heavy metal detoxification in contaminated environments like tannery effluent and mining processes.

Isolation and Identification of Chromium-Reducing Bacteria from Challawa Industrial Area Kano State, Nigeria

Chromium (Cr) is toxic, mutagenic, carcinogenic, and harmful to most plants, animals, and bacteria inhabiting aquatic environments because it is motile, highly toxic, soluble in water and it is a good oxidizing agent and it is detrimental to cell membranes. Chromium remediation with the help of microorganisms is believed to be the best and cheaper technology at hand to clean up Cr contamination, some chromium resistant bacteria can reduce chromium (VI) to (III) with the help of reductase enzymes. This research was aimed to isolate and identify bacteria capable of reducing chromium from tannery effluent. The level of chromium from different tannery industries was analyzed using Microwave Plasma Atomic Absorption Spectroscopy (MPAES) and compared to Environmental Protection Agency (EPA) standard which shows that all the samples were above the EPA standard except for one sample, a pour plating method was used to isolate the bacteria on Luria Bertani (LB) amended with K2Cr2O7 after serial dilution, the isolate was identified morphologically, biochemically and molecularly as Acetanaerobacter sp. based on 16s rRNA gene sequencing and molecular phylogenetic analysis, Atomic absorption spectrophotometry was carried out to determine the level of chromium from the bio-reduced sample. A reduction of 18.32% was observed in broth treated with the isolate within 48 hours of incubation at 37°C.

Enhancement of chromium removal and energy production simultaneously using iron scrap as anodic filling material with pyrite-based constructed wetland-microbial fuel cell

Iron scraps was used as the anodic filling material coupled with pyrite as a substrate in a constructed wetland-microbial fuel cell (IsAno-PS) to investigate the power production and treatment of simulated wastewater that contained chromium. During 76 days of operation, the IsAno-PS facilitated the removal of total chromium, ammonia nitrogen, total phosphorus and energy production because of the synergetic effect between pyrite and iron scraps (p < 0.05). By XRD analysis and microbial composition analysis, chemical reduction (adsorption, complexation and reduction) and biological reduction were determined during the chromium removal reaction. According to alpha and beta diversity of microbial community composition in the system, the microbial community was significantly (p < 0.05) influenced by iron scraps. Electrically active bacteria like Firmicutes, were highly enriched, while the Fe (III)-reducing bacteria Geobacter and chromium-reducing bacteria Bacilli increased in the IsAno-PS. In network analysis, adding iron scraps was accompanied by distinct microbial communities, which could conductive to the bioremediation of chromium and participate in nitrogen cycle. Furthermore, Chloroflexi, which related to iron and sulfur cycling was identified as a module hub, implying taxa with low abundances can have important roles in ecosystem function. Iron scraps could affect the chromium removal by regulating the production of EPS. Chromate reductase (ChrR) gene decreased due to Fe2+ released by iron scraps. Overall, iron scraps used as the anodic filling material coupled with pyrite as a substrate in CW-MFCs could be an efficient configuration CW-MFC.

Differential transformation mechanisms of exotic Cr(VI) in agricultural soils with contrasting physio-chemical and biological properties

The transformation mechanisms of Cr(VI) in agricultural soils at the molecular level remain largely unknown due to the multitude of abiotic and biotic factors. In this study, the different speciation and distribution of Cr in two types of agricultural soil (Ultisol and Fluvo-aquic soils) after two weeks of aging was investigated using synchrotron-based X-ray absorption near-edge structure (XANES) spectroscopy, microfocused X-ray fluorescence (μ-XRF) and X-ray transmission microscopy (STXM). The microbial community structure of the two soils was also analyzed via high-throughput sequencing of 16S rRNA. Cr(VI) availability was relatively lower in the Ultisol than in the Fluvo-aquic soil after aging. Cr K-edge bulk XANES and STXM analysis indicated that Cr(VI) was reduced to Cr(III) in both soils. μ-XRF analysis and STXM analysis indicated the predominant association of Cr with Mn/Fe oxides and/or organo-Fe oxides in both soils. Additionally, STXM-coupled imaging and multiedge XANES analyses demonstrated that carboxylic groups were involved in the reduction of Cr(VI) and subsequent retention of Cr(III). 16S rRNA analysis showed considerably different bacterial communities across the two soils. Redundancy analysis (RDA) suggested that soil properties, including the total carbon content, Fe oxide component and pH, were closely linked to Cr(VI)-reducing functional bacteria in the Ultisol, including chromium-reducing bacteria (CRB) (e.g., Bacillus sp.) and dissimilatory iron-reducing (DIRB) (e.g., Shewanella sp.) bacteria, which possibly promoted Cr(VI) reduction. These findings shed light on the molecular-level transformation mechanisms of Cr(VI) in agricultural soils, which facilitates the effective management of Cr-enriched farmland.

Operational Characteristics of Immobilized Ochrobactrum sp. CUST210-1 Biosystem and Immobilized Chromate Reductase Biosystem in Continuously Treating Actual Chromium-Containing Wastewater

Cr(VI) detoxification by biotreatment is considered one of the most practical detoxification methods, especially at low-to-medium concentrations. Although the capabilities of chromium-reducing bacteria and related enzymes in removing Cr(VI) have been explored, little is known about their differences in engineering applications. In this study, Ochrobactrum sp. CUST210-1 was isolated and its chromate reductase identified and separated as biological elements in biosystems developed for Cr(VI) removal. Results indicate that intracellular Cr(OH)3(s) accounted for 88.01% of Cr(VI) reduction product, and a possible reduction mechanism was exposed. The chromate reductase in Ochrobactrum sp. CUST210-1 was ChrR protein, and its crystal structure was revealed. The toxicity of Cr(VI)-containing wastewater was decreased by 57.8% and 67.0% (at minimum) by the CUST210-1 strain and ChrR, respectively. The Ochrobactrum sp. CUST210-1 biosystem demonstrated good adaptability to pH (7–9), and the ChrR biosystem exhibited high removal efficiency (&gt;98.2%) at a wide range of temperatures (25 °C–40 °C). The outlet Cr(VI) concentration of the CUST210-1 biosystem met the industrial discharge limit of 0.5 mg L−1 when the inlet Cr(VI) concentration in the actual Cr(VI)-containing wastewater was &lt;430 mg L−1. The stricter water quality standard of 0.05 mg L−1 could be complied with by the immobilized ChrR biosystem when &lt;150 mg L−1 Cr(VI) concentration was introduced. These developed biosystems can be used in the bioremediation of various Cr(VI)-contaminated wastewaters. Regarding capital costs, those of the CUST210-1 biosystem were higher. To our knowledge, this is the first report comparing differences in the economic and operational characteristics of bacteria and enzyme biosystems for Cr(VI) removal.

Reduction of Cr(VI) by Bacillus species isolated from tannery effluent contaminated sites of Tamil Nadu, India

Hexavalent chromium [Cr(VI)] is a heavy metal pollutant in the environment released through leather tanning. In this context, the present study was envisaged to isolate and identify chromium reducing bacteria in order to employ them towards detoxification of chromium. In general, bacteria are ecofriendly and cost-effective which can be efficiently used in bioremediation processes. The collected tannery effluents yielded considerable Bacillus species. These isolates demonstrated well for their resistance which showed exceptional Cr(VI) reduction within 48 h under aerobic conditions. Mostly, chromium resistance confers through Chromate transporters which involves metabolic reduction of toxic Cr(VI) to non-toxic Cr(III). Distribution of chr genes in Bacillus species were identified from their genome through UniProt. Treatment of raw tannery effluent employing these isolates individually or as a consortia reduced Cr(VI) significantly. Thus, these bacterial strains, could evolve as a potential organisms to reduce toxic Cr(VI) to its non-toxic Cr(III) form in chromium contaminated sites.

Application of enhanced bioreduction for hexavalent chromium-polluted groundwater cleanup: Microcosm and microbial diversity studies

Hexavalent chromium (Cr6+) is a commonly found heavy metal at polluted groundwater sites. In this study, the effectiveness of Cr6+ bioreduction by the chromium-reducing bacteria was evaluated to remediate Cr6+-contaminated groundwater. Microcosms were constructed using indigenous microbial consortia from a Cr6+-contaminated aquifer as the inocula, and slow-releasing emulsified polycolloid-substrate (ES), cane molasses (CM), and nutrient broth (NB) as the primary substrates. The genes responsible for the bioreduction of Cr6+ and variations in bacterial diversity were evaluated using metagenomics assay. Complete Cr6+ reduction via the biological mechanism was observed within 80 days using CM as the carbon source under anaerobic processes with the increased trivalent chromium (Cr3+) concentrations. Cr6+ removal efficiencies were 83% and 59% in microcosms using ES and NB as the substrates, respectively. Increased bacterial communities associated with Cr6+ bioreduction was observed in microcosms treated with CM and ES. Decreased bacterial communities were observed in NB microcosms. Compared to ES, CM was more applicable by indigenous Cr6+ reduction bacteria and resulted in effective Cr6+ bioreduction, which was possibly due to the growth of Cr6+-reduction related bacteria including Sporolactobacillus, Clostridium, and Ensifer. While NB was applied for specific bacterial selection, it might not be appropriate for electron donor application. These results revealed that substrate addition had significant impact on microbial diversities, which affected Cr6+ bioreduction processes. Results are useful for designing a green and sustainable bioreduction system for Cr6+-polluted groundwater remediation.

Study on Ochrobactrum pseudintermedium ADV31 for the removal of hexavalent chromium through different immobilization techniques

Chromium (VI) is one of the toxic heavy metals causing various human ailments like asthma to severe forms of cancer; hence, its removal from industrial effluents is essential. The present study demonstrates ameliorating techniques for the removal of Cr(VI). A chromium-reducing bacterium (CRB) identified as Ochrobactrum pseudintermedium ADV31 through 16S rRNA gene sequencing, was found to remove concentrations of Cr(VI) up to 600 mg/L in nutrient medium. Calcium alginate (CA) and polyurethane foam (PUF) were the two different materials used for the immobilization of Ochrobactrum pseudintermedium ADV31. The efficiency of the immobilized cells and free form of bacterial cells with inoculum concentrations of 1% and 5% were compared for the removal of Cr(VI). Calcium alginate with 5% inoculum concentrations showed removal of 82% of 600 mg/L in 5 days, while PUF with 5% inoculum size showed removal up to 86% of 600 mg/L in 5 days. Free form of bacterial cell was able to remove 36.7%. The bacterium was able to tolerate a wide range of pH ranging from 6 to 9 and had an optimum temperature of 45 °C. The results confirmed that both forms of immobilization methods are equally effective for the removal of hexavalent chromium and can be used for various biotechnological processes for the metal bioremediation.

Biological remediation of chromium (VI) in aquifer media columns

Hexavalent chromium (Cr(VI)) is highly soluble in water, but is widely used in industrial sectors for many purposes. The effluent from these industrial activities is often released to the environment posing a threat to aquatic life and to humans. Conventional methods of treating Cr(VI) often require the use of pump and treat methods followed by the use of harmful toxic chemicals that are hard to dispose of and usually are expensive. The study explores reduction of Cr(VI) to Cr(III) using biological means (a popular issue of bioremediation of contaminated aquifer) in columns; control with aquifer media, system 1 inoculated with CRB (chromium reducing bacteria) dried sludge, system 2 further amended with saw dust and system 3 amended with vegetative material from target site as carbon source. CRB are essential and were inoculated in the columns (system 1-3) as dried sludge, previously isolated (Enterococcus casseliflavus, Pseudomonas putida, C.istrobacter sedlakii, Enterobacter cloacae and Enterobacter hormaechei) and tested in a batch system. The column reactors were run for 60 days at concentrations 40, 60 and 80 mg/L. Culture isolates in the effluent of the reactors were isolated and identified. Complete reduction was observed from all columns under different concentrations, with some failures at certain periods before quasi steady state (determined after 40 d). At 40 mg/L more than 95 % of Cr(VI) was reduced across the spectrum. System 3 best reduced Cr(VI) compared to other treatment column reactors at high concentrations of 80 mg/L. System 2 carbon source didn’t enhance Cr(VI) reduction compared to Syetem 1 with no carbon material. Algae growth was observed in the columns after operating for 40 d at 40 mg/L. Using 18s rRNA the dominant algae was identified as Chlamydomonas debaryana. As Cr(VI) concentration was increased, both CRB and the algae were assumed to be in synergy as Cr(VI) was reduced at influent concentration as high as 80 mg/L (double the concentration from the site). Further investigation was done in the study to identify Cr(VI) reducing potential by algae. The use of vegetative material from the target site in the presence of algae proved to enhance Cr(VI) reduction by CRB even though saw dust did not perform as expected. This method has potential to be used in Cr polluted sites in South Africa with careful application.

Microbial chromium (VI) immobilization in saturated aquifer columns using culture inoculated soil

Chromium exists in two oxidation states in the environment namely; Cr(VI) which is highly toxic, carcinogenic and mutagenic in nature and Cr(III) which is less toxic, mobile and is required in trace elements with human diets. South Africa holds approximately 72 % of the currently documented chromium ore reserves. Areas where chromium is mined, experience severe Cr(VI) contamination due to poor treatments of Cr(VI) by products. Cr(VI) is exclusively released through anthropogenic activities into wastewaters. Biological reactors have been investigated in reducing chromium successfully. Bioremediaion of Cr(VI) to Cr(III) has increasingly gained interest as it is seen as economic and ecological. In this study, in situ bioremediation of treating Cr(VI) aquifers is evaluated. Firstly, dried sludge containing indigenous chromium reducing bacteria (CRB) from a dried sludge was collected from Brits Wastewater Treatment Plant, North West Province (South Africa). Batch experiments by isolated bacteria were done under aerobic conditions. Cr(VI) reduction was recorded at 50, 100, 200 and 400 mg/L of Cr(VI) concentrations. Pseudomonas putida showed complete Cr(VI) reduction within 5 h of batch analysis. The continuous batch experiments were done using columns with five equally spaced sampling pots along the column length. Cr(VI) reduction profile was thus observed. At steady state there was complete reduction of Cr(VI) on all the columns including; sludge, saw dust and carbon source at 40 mg/L. The continuous batch system appeared to have certain amount of algae emerging after 30 d of operation, from the bottom of the column where there’s reduced Cr(VI) concentration and so it was cultivated and characterized. The presence of algae may show a symbiosis relationship involving a complex relationship of detoxification survival of algae or a food source for bacteria. Cr(VI) reducing effects of the columns was further tested against higher Cr(VI) concentrations at 60 mg/L. Near complete Cr(VI) reduction was observed within a couple of days of operation at this concentration. This study demonstrates the potential of biological Cr(VI) reduction using Cr(VI) reducing bacteria that has been isolated from polluted sites in South Africa.

Draft Genome Sequence of a Chromium-Reducing Strain, Pseudomonas fluorescens S613, Isolated from a Chromium-Contaminated Aquifer in Los Alamos, New Mexico.

ABSTRACTIn this report, a chromium-reducing bacterium, Pseudomonas fluorescens strain S613, was isolated from a Cr(VI)-contaminated aquifer at Los Alamos, NM, and sequenced. The size of the draft genome sequence is approximately 6.7 Mb.

The reduction of chromium (VI) phytotoxicity and phytoavailability to wheat (Triticum aestivum L.) using biochar and bacteria

Chromium (Cr) is considered a serious environmental pollutant due to its wide industrial use. Toxicity of Cr to plants depends on its valence state. Cr(VI) is highly toxic and mobile whereas Cr(III) is less toxic. Cr accumulation in plants causes high toxicity in terms of alterations in the germination process, reduction in the growth of roots, stems, and leaves, which may affect total dry matter production and yield. We performed a pot experiment to investigate chromium (50mgkg−1) induced phytotoxicity in wheat (Triticum aestivum L.) and to reduce its phytoavailability by amending the contaminated soil with chromium reducing bacteria (CRB) and 1% or 5% biochar.For the phytotoxicity assay, wheat was grown at different concentrations of chromium (10, 20, 30, 40 and 50mgL−1). After 3 weeks a subsequent reduction in root and shoot length, fresh and dry biomass, percentage germination, total chlorophyll, and carbohydrates was observed.Our results showed reduction in phytotoxic effects of Cr(VI) mainly due to a reduction of toxic Cr(VI) to Cr(III). Highest reductive transformation of Cr(VI) to Cr(III) was observed in T9 (5% biochar with bacterial consortia) in all three matrices i.e. soil (99%), root (98%) and shoots (97%). The highest (90%) Cr retention within soil was also observed in T9 with the addition of 5% biochar and bacterial consortia. Of the remaining 10% Cr retention (entering into the plant), 3mgkg−1 and 1.3mgkg−1 was found in roots and shoots (on dry weight basis), respectively. Soil inoculation with consortia showed 33% higher stabilization than individual strain application. Soil amendment with biochar and bacteria showed an improvement in plant height, biomass production, seed germination, chlorophyll, protein, and carbohydrate content (p<0.05). Findings of this study may help to reduce food chain availability of potentially toxic Cr by employing cost-effective bioremediation amendments.

Genome Sequence of a Chromium-Reducing Strain, Bacillus cereus S612.

We report here the genome sequence of an effective chromium-reducing bacterium, Bacillus cereus strain S612. The size of the draft genome sequence is approximately 5.4 Mb, with a G+C content of 35%, and it is predicted to contain 5,450 protein-coding genes.

A Novel Subspecies of Staphylococcus aureus from Sediments of Lanzhou Reach of the Yellow River Aerobically Reduces Hexavalent Chromium

Background: Lanzhou reach of the Yellow River is contaminated by heavy metals including chromium perennially. The microbial community within the sediment is very active. Yet the study on the bacteria in this distinctive microbial community is still scarce. Results: LZ-01, a Gram-positive hexavalent chromium-reducing bacterium was isolated from the soil sample collected at a petrochemical corporation wastewater discharge site of Lanzhou reach. It was able to aerobically reduce 94.5% of 0.4 mM Cr (VI) to Cr(III) in 120 hours. Cd (II) and NaN 3 treatment both repressed Cr(VI) reduction in LZ-01 and Cr(III) precipitates were detected both on the cell membrane and in the cytoplasm by Transmission Electron Microscopy (TEM) imaging. LZ-01 also demonstrated resistance to 4 mM As (V) and 9 mM U (VI). LZ-01 was closely related to Staphylococcus aureus revealed by 16S rRNA sequence analysis. Comparison of cellular fatty acid components and Vitek phenotype identification provided further evidences that LZ-01 is a novel subspecies of S. aureus. Conclusions: A chromate-reducing bacterium LZ-01 identified as a novel subspecies of S. aureus was isolated from Lanzhou reach of the Yellow River. Cd (II) and NaN 3 treatment and TEM images suggested that Cr(VI) was reduced not only intracellularly but also on the cell membrane. All the results indicate that the isolate has a great potential for bioremediation of Cr (VI)-contaminated environment.

Laboratory scale column studies on transport and biotransformation of Cr(VI) through porous media in presence of CRB, SRB and IRB

Studies were conducted to understand the transport and biotransformation of Cr(VI) through porous media in presence of chromium reducing bacteria (CRB), sulphate reducing bacteria (SRB) and iron reducing bacteria (IRB). Column experiments were conducted using sand and soil, and different bacterial strains working individually and in combination. Results showed that 20mg/L of Cr(VI) in the feed was completely contained within 500–648h by different combinations of bacterial strains. A one-dimensional mathematical model, based on advection–dispersion–adsorption equations for transport of Cr(VI) and molasses in saturated, homogeneous porous medium, coupled with Monod's inhibition kinetics for immobile bacteria was able to simulate the experimental results satisfactorily. The proposed mathematical model will be very helpful in the development of a management model for in situ bioremediation of chromium contaminated aquifers using either reactive zones or bio-barriers.

Experimental and mathematical modeling studies on Cr(VI) reduction by CRB, SRB and IRB, individually and in combination

Cr(VI) reduction studies were carried out with chromium reducing bacteria (CRB), sulphate reducing bacteria (SRB) and iron reducing bacteria (IRB), individually and in combination. Biokinetic parameters such as maximum specific growth rate ( μ max), half saturation constant ( K s), yield coefficient ( Y T) and inhibition coefficient ( K i ) for individual cultures were evaluated. A mathematical model was proposed for simulating the chromium reduction, COD utilization and biomass growth, by individual cultures as well as by a combination of two or three different cultures, for different initial Cr(VI), SO 4 2− and Fe(III) concentrations. The biokinetic parameters evaluated from one set of experiments for individual cultures were utilized in all the validation studies. The performance of the mathematical model in terms of the dimensionless modified coefficient of efficiency ( E) indicated that the proposed model simulates the system behavior very well.