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

Myco-remediation of chromium heavy metal from industrial wastewater: A review

Chromium a heavy metal present in the effluent of the industries causes accumulation of toxicity in water. Chromium commonly has Cr (III) and Cr (VI), two oxidation states, in which hexavalent form causes more health issues to human, other species and environment. The increased anthropogenic effects, especially tannery industrial effluent contributes the higher percentage of chromium accumulation. Removal of heavy metal can be attributed to many aspects, conventionally the physio-chemical methods which superseded by biological means of remediation. Chromium resistant microbes can be used to remove metal ions of chromium from the effluent, as this can be considered an eco-friendly approach. The microbial accession of nanoparticles synthesis is being focused, due to its accuracy and specificity in results. Mycoremediation grabbed attention as fungal absorbance efficiency and the surface-mechanism of heavy metal ions correlates each other. Current study in-depth indulges the base to core mechanism of mycoremediation of chromium ions from different effluents. Fungal-assisted mechanism of chromium ions have insists to be fewer, which may gain attention by enhancing the methodology of removal of chromium ions. This study focuses on improvement of fungal strain and pave-way, to improvise the study with immobilization technique which renders usage of the adsorbents redundant usage and applications, substantially with the low-cost polymeric material alginate is given more importance for immobilization technique. Alginate apart from low-cost adsorbent, is an excellent support for fungal producing nanoparticles which would provide wide-cast and an extraordinary adsorbent material.

DIET-like and MIET-like mutualism of S. oneidensis MR-1 and metal-reducing function microflora boosts Cr(VI) reduction

Microbial treatment of Cr(VI) is an environmentally friendly and low-cost approach. However, the mechanism of mutualism and the role of interspecies electron transfer in Cr(VI) reducing microflora are unclear. Herein, we constructed an intersymbiotic microbial association flora to augment interspecies electron transfer via functionalizing electroactive Shewanella oneidensis MR-1 with metal-reducing microflora, and thus the efficiency of Cr(VI) reduction. The findings suggest that the metal-reducing active microflora could converts glucose into lactic acid and riboflavin for S. oneidensis MR-1 to act as a carbon source and electron mediator. Thus, when adding initial 25 mg/L Cr (VI), this microflora exhibited an outstanding Cr (VI) removal efficiency (100%) at 12 h and elevated Cr (III) immobilization efficiency (80%) at 60 h with the assistance of 25 mg/L Cu(II). A series of electrochemical experiments proved this remarkable removal efficiency were ascribed to the improved interspecies electron transfer efficiency through direct interspecies electron transfer and riboflavin through mediated interspecies electron transfer. Furthermore, the metagenomic analysis revealed the expression level of the electron transport pathway was promoted. Intriguing high abundance of genes participating in the bio-reduction and biotransformation of Cr(VI) was also observed in functional microflora. These outcomes give a novel strategy for enhancing the reduction and fixation of harmful heavy metals by coculturing function microflora with electrogenic microorganisms.

Genotoxicity responses of single and mixed exposure to heavy metals (cadmium, silver, and copper) as environmental pollutants in Drosophila melanogaster

Heavy metals are now persistently present in living things' environments, in addition to their potential toxicity. Therefore, the aim of this study was to utilize D. melanogaster to determine the biological effects induced by different heavy metals including cadmium chloride (CdCl2), copper (II) sulfate pentahydrate (CuSO 4.5 H2O), and silver nitrate (AgNO3). In vivo experiments were conducted utilizing three low and environmentally relevant concentrations from 0.01 to 0.5 mM under single and combined exposure scenarios on D. melanogaster larvae. The endpoints measured included viability, reactive oxygen species (ROS) generation and genotoxic effects using Comet assay and the wing-spot test. Results indicated that tested heavy metals were not toxic in the egg-to adult viability. However, combined exposure (CdCl2+AgNO3 and CdCl2+AgNO3+CuSO 4.5 H2O) resulted in significant genotoxic and unfavorable consequences, as well as antagonistic and/or synergistic effects on oxidative damage and genetic damage.

Role of chromium reductases, antioxidants, and biosorption against oxidative damage of metals by Bacillus cereus

Current research was performed to look for the performance of Bacillus cereus PY3 for metal detoxification. Strain PY3 was recognized as B. cereus using 16 S rRNA. Higher rate of removal of Zn and Cr (VI) by PY3 was obtained between pH 6-8 and 100-500 µg/mL in 24 h. Highest removal of Cr6+ by strain PY3 was achieved at acidic, neutral, and alkaline atmosphere, 100-300 µg Cr6+ /mL and 25-35°C. Supernatant of PY3 detoxified Cr6+ into Cr3+ then cell pellet (debris) adsorbed them. The mechanism of metal removal was due to the release of cytolic extracts. Release of antioxidants and bio-film played a protective role against cell damage. Metals increased antioxidants and bio-film formation. SEM images showed the smooth external structure of PY3 when cells were exposed to metals thus confirming the role of cells for detoxification. Results Above facts conclude that PY3 can remove metallic pollution in polluted soil.

Performance and mechanism of chromium reduction in denitrification biofilm system with different carbon sources

In the process of biological reduction of Cr(VI), the type of carbon sources affects the rate and effect of Cr(VI) reduction, but its specific performance and influencing mechanism have not yet been explored. In this study, four denitrification biofilm reactors were operated under four common carbon sources (C6H12O6, CH3COONa, CH3OH, CH3COONa:C6H12O6 1:1) to reveal the impact of carbon sources on Cr(VI) reduction. Through preliminary experimental concentration research, 75 mg/L Cr(VI) was selected as the dosing concentration. In long-term operation, the composite carbon sources of CH3COONa and C6H12O6 demonstrated excellent stability and achieved an impressive Cr(VI) removal efficiency of 99.5 %. The following sequence was C6H12O6, CH3COONa, and CH3OH. Among them, CH3OH was less competitive and the system was severely unbalanced with lowest Cr(VI) reduction efficiency. The toxicity reactions, changes in EPS and its functional groups, and electron transfer revealed the reduction and fixation mechanism of chromium on denitrification biofilm. The changes in microbial communities indicated that microbial communities in composite carbon sources can quickly adapt to the high toxic environment. The proportion of Trichococcus reached 43.6 %, which played an important role in denitrification and Cr(VI) reduction. Meanwhile, the prediction of microbial COG function reflected its excellent metabolic ability and defense mechanism.

Ochrobactrum chromiisoli sp. nov., Isolated from Chromium-Contaminated Soil

A Gram-stain-negative, non-spore-forming, flagellated, motile, aerobic, rod-shaped bacteria strain, designated YY2XT, was isolated from chromium-contaminated soil. Phylogenetic analysis based on 16S rRNA gene, recA gene, and whole genome indicated that the strain represented a new member of the genus Ochrobactrum, family Brucellaceae, class Alphaproteobacteria. The phylogenetic trees based on 16 s rRNA gene, revealed that Falsochrobactrum ovis DSM26720T (96.7%), Ochrobactrum gallinifaecis DSM15295T (96.2%), and Pseudochrobactrum asaccharolyticum DSM25619T (96.2%) are the most closely related phylogenetic neighbors of strain YY2XT. The draft genome of YY2XT was approximately 4,650,646 bp in size with a G + C content of 53.0 mol%. Average nucleotide identity and digital DNA-DNA hybridization values among strain YY2XT and the selected Brucellaceae species were 71.4-83.1% and 13.5-42.7%, which are below the recommended cut-off values for species delineation. Growth of strain YY2XT occurred within pH 5-10 (optimum, pH 7-8), 4 ℃-42 °C (optimum, 30 °C), and NaCl concentrations of 0.0-6.0% (optimum, 1.0%). Major quinone system was ubiquinone 10, the major fatty acids were C16:0, C18:1ω7c, and C16:1ω7c and the major polyamines were spermidine and putrescine. Major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, phosphatidylmonomethylethanolamine, phosphatidylethanolamine, and four undefined lipids. On the basis of the phenotypic, genotypic and chemotaxonomic traits, strain YY2XT was considered to represent a novel species of the genus Ochrobactrum, for which the name Ochrobactrum chromiisoli sp. nov. is proposed. The type strain is YY2XT (= CCTCC AB 2023035T = JCM 36000T).

Reduction of Chromate via Biotic and Abiotic Pathways in the Presence of Three Co-contaminating Electron Acceptors

Bioreduction of Cr(VI) to Cr(III) is a promising technology for removing Cr(VI), but Cr(VI) reduction alone cannot support microbial growth. This study investigated the reduction of Cr(VI) in the presence of three electron acceptors that typically coexist with Cr(VI): NO3-, SO42-, and Fe(III). All three systems could reduce Cr(VI) to Cr(III), but the fate of Cr, its impacts on reduction of the other acceptors, and its impact on the microbial community differed. Although Cr(VI) was continuously removed in the NO3--reduction systems, batch tests showed that denitrification was inhibited primarily through impeding nitrite reduction. The SO42- and Fe(III) reduction systems reduced Cr(VI) using a combination of biotic and abiotic processes. Across all three systems, the abundance of genera capable of reducing Cr(VI) increased following the introduction of Cr(VI). Conversely, the abundance of genera that cannot reduce or resist Cr(VI) decreased, leading to restructuring of the microbial community. Furthermore, the abundance of sulfide oxidizers and Fe(II) oxidizers substantially increased after the introduction of chromate. This study provides fundamental knowledge about how Cr(VI) bioreduction interacts with bioreductions of three other co-contaminating electron acceptors.

Hexavalent chromium removal by a resistant strain Bacillus cereus ZY-2009

Bioreduction of Cr(VI) to Cr(III) by reducing microbes has attracted increasing concern. Here, Cr(VI) removal capacity of a Cr(VI)-resistant bacterium isolated from activated sludge was investigated. Based on its physio-biochemical attributes and 16S rDNA sequence analysis, the strain was identified as Bacillus cereus ZY-2009. It grew normally in the media containing 10-100 mg/L Cr(VI), indicating its high resistance to Cr(VI). Under the optimal conditions of pH 7.0, inoculation amount 10%, and temperature 30°C, Cr(VI) was effectively removed, with a removal rate of ∼80%. Co-existing Fe³⁺ and Cu²⁺ greatly increased Cr(VI) removal, but Cd²⁺ showed significant inhibition. Cr(VI) was removed mainly via enzyme-mediated bioreduction but not biosorption. Cr(VI) was reduced by different cell fractions (i.e. extracellular secretions, cytoplasm, and cell envelope), implying that Cr(VI) can be reduced both extracellularly and intracellularly. This strain can be used in the bioremediation of Cr(VI)-containing wastewater, with Fe³⁺ and Cu²⁺ as stimulators.

Structure of the O-specific polysaccharide of Ochrobactrum endophyticum KCTC 42485T containing 3-(3-hydroxy-2,3-dimethyl-5-oxoprolyl)amino-3,6-dideoxy-d-galactose

Ochrobactrum endophyticum (syn. Brucella endophytica) is an aerobic species of Alphaproteobacteria isolated from healthy roots of Glycyrrhiza uralensis. Here we report the structure of the O-specific polysaccharide obtained by mild acid hydrolysis of the lipopolysaccharide of the type strain KCTC 42485:→3)-α-l-FucpNAc-(1→3)-β-d-QuipNAc-(1→2)-β-d-Fucp3NAcyl-(1→ where Acyl is 3-hydroxy-2,3-dimethyl-5-oxoprolyl. The structure was elucidated using chemical analyses along with ¹H and ¹³C NMR spectroscopy (including ¹H,¹H COSY, TOCSY, ROESY and ¹H,¹³C HSQC, HMBC, HSQC-TOCSY and HSQC-NOESY experiments). To our knowledge the OPS structure is novel and has not been previously published.

Synergy of surface adsorption and intracellular accumulation for removal of uranium with Stenotrophomonas sp: Performance and mechanisms

Uranium is well-known to have serious adverse effects on the ecological environment and human health. Bioremediation stands out among many remediation methods owing to its being economically feasible and environmentally friendly. This study reported a great promising strategy for eliminating uranium by Stenotrophomonas sp. CICC 23833 in the aquatic environment. The bacterium demonstrated excellent uranium adsorption capacity (q_max = 392.9 mg/g) because of the synergistic effect of surface adsorption and intracellular accumulation. Further analysis revealed that hydroxyl, carboxyl, phosphate groups and proteins of microorganisms were essential in uranium adsorption. Intracellular accumulation was closely related to cellular activity, and the efficiency of uranium processing by the permeabilized bacterial cells was significantly improved. In response to uranium stress, the bacterium was found to release multiple ions in conjunction with uranium adsorption, which facilitates the maintenance of bacterial life activities and the conversion of uranyl to precipitates. These above results indicated that Stenotrophomonas sp. Had great potential application value for the remediation of uranium.

PMo12 as a redox mediator for bio-reduction of Cr(VI): Promotor or inhibitor?

Slow reduction rate and low reduction ability were the main limitations of bio-reduction of Cr(VI). As an efficient redox mediator, how phosphomolybdic acid (PMo₁₂) affected bio-reduction of Cr(VI) was worthy of exploration. In this study, short-term and long-term effects of PMo₁₂ on Cr(VI) reduction were investigated to reveal the relevant mechanism. After evaluating the short-term effect of PMo₁₂ concentration from 0.05 to 1.00 mM on Cr(VI) bio-reduction, 0.50 mM was found to be optimum by improving Cr(VI) reduction rate by 16.3 % and microbial electron transport system activity (ETSA) by 43.0 % with Cr(VI) reduction efficiency of 100 % in short-term (22 h) batch experiments. By contrast, in long-term (28 days) continuous flow experiments, 0.50 mM PMo₁₂ exhibited serious inhibition on Cr(VI) bio-reduction. The cumulative toxicity of Mo, strong oxidative stress (reactive oxygen species increased by 16.5 %), the inhibition of extracellular polymeric substances production and the reduction of microbial activity were proved to be the main inhibition mechanism. In terms of microbial electron transport system, the main electron carriers including flavin mononucleotide (FMN), nitrate reductase (NAR), nitrite reductase (NIR) were seriously inhibited. BugBase analysis confirmed that the relative abundance of biofilm forming bacteria decreased after PMo₁₂ addition, and the relative abundance of oxidative stress tolerance bacteria continued to increase.

Applied of actinobacteria consortia-based bioremediation to restore co-contaminated systems

Global industrialization and natural resources extraction have left cocktails of environmental pollutants. Thus, this work focuses on developing a defined actinobacteria consortium able to restore systems co-contaminated with pollutants occurring in Argentinian environments. In this context, five actinobacteria were tested in solid medium to evaluate antagonistic interactions and tolerance against lindane (LIN), Reactive Black B-V (RBV), phenanthrene (Ph) and Cr(VI). The strains showed absence of antagonism, and most of them tolerated the presence of individual pollutants and their mixtures, except Micromonospora sp. A10. Thus, a quadruple consortium constituted by Streptomyces sp. A5, M7, MC1, and Amycolatopsis tucumanensis DSM 45259^T, was tested in liquid systems with individual contaminants. The best microbial growth was observed in the presence of RBV and the lowest on Cr(VI). Removals detected were 83.3%, 65.0% and 52.4% for Ph, RBV and LIN, respectively, with absence of Cr(VI) dissipation. Consequently, the consortium performance was tested against the organic mixture, and a microbial growth similar to the biotic control and a LIN removal increase (61.2%) were observed. Moreover, the four actinobacteria of the consortium survived the mixture bioremediation process. These results demonstrate the potential of the defined actinobacteria consortium as a tool to restore environments co-contaminated with organic pollutants.

A comprehensive review on bio-stimulation and bio-enhancement towards remediation of heavy metals degeneration

Pollution of heavy metals is one of the risky contaminations that should be managed for all intents and purposes of general well-being concerns. The bioaccumulation of these heavy metals inside our bodies and pecking orders will influence our people in the future. Bioremediation is a bio-mechanism where residing organic entities use and reuse the squanders that are reused to one more form. This could be accomplished by taking advantage of the property of explicit biomolecules or biomass that is equipped for restricting by concentrating the necessary heavy metal particles. The microorganisms can't obliterate the metal yet can change it into a less harmful substance. In this unique circumstance, this review talks about the sources, poisonousness, impacts, and bioremediation strategies of five heavy metals: lead, mercury, arsenic, chromium, and manganese. The concentrations here are the ordinary strategies for bioremediation such as biosorption methods, the use of microbes, green growth, and organisms, etc. This review demonstrates the toxicity of heavy metal contamination degradation by biotransformation through bacterioremediation and biodegradation through mycoremediation.

Deciphering Cadmium (Cd) Tolerance in Newly Isolated Bacterial Strain, Ochrobactrum intermedium BB12, and Its Role in Alleviation of Cd Stress in Spinach Plant (Spinacia oleracea L.)

A cadmium (Cd)-tolerant bacterium Ochrobactrum intermedium BB12 was isolated from sewage waste collected from the municipal sewage dumping site of Bhopal, India. The bacterium showed multiple heavy metal tolerance ability and had the highest minimum inhibitory concentration of 150 mg L-1 of Cd. Growth kinetics, biosorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared (FTIR) spectroscopy studies on BB12 in the presence of Cd suggested biosorption as primary mode of interaction. SEM and TEM studies revealed surface deposition of Cd. FTIR spectra indicated nitrogen atom in exopolysaccharides secreted by BB12 to be the main site for Cd attachment. The potential of BB12 to alleviate the impact of Cd toxicity in spinach plants (Spinacia oleracea L.) var. F1-MULAYAM grown in the soil containing Cd at 25, 50, and 75 mg kg-1 was evaluated. Without bacterial inoculation, plants showed delayed germination, decrease in the chlorophyll content, and stunted growth at 50 and 75 mg kg-1 Cd content. Bacterial inoculation, however, resulted in the early germination, increased chlorophyll, and increase in shoot (28.33%) and root fresh weight (72.60%) at 50 mg kg-1 of Cd concentration after 75 days of sowing. Due to bacterial inoculation, elevated proline accumulation and lowered down superoxide dismutase (SOD) enzyme activity was observed in the Cd-stressed plants. The isolate BB12 was capable of alleviating Cd from the soil by biosorption as evident from significant reduction in the uptake/translocation and bioaccumulation of Cd in bacteria itself and in the plant parts of treated spinach. Potential PGP prospects and heavy metal bioremediation capability of BB12 can make the environmental application of the organism a promising approach to reduce Cd toxicity in the crops grown in metal-contaminated soils.

Biotreatment potential of co-contaminants hexavalent chromium and polychlorinated biphenyls in industrial wastewater: Individual and simultaneous prospects

Co-existence of polychlorinated biphenyls (PCBs) and hexavalent chromium (Cr(VI)) in the environment due to effluent from industries has aggravated the pollution problem. Both contaminants can alter chemical interactions, processes and impair enzymatic activities in the ecosystem that results in negative impacts on aquatic and terrestrial life. Previously, research has been performed for the fate and transfer of these contaminants individually, but simultaneous removal approaches have not received much attention. Cr(VI) exists in a highly toxic form in the environment once released, whereas location of chlorine atoms in the ring determines PCBs toxicity. Lower chlorinated compounds are easily degradable whereas as high chlorinated compounds require sequential strategy for transformation. Microorganisms can develop different mechanism to detoxify both pollutants. However, occurrence of multiple contaminants in single system can alter the bioremediation efficiency of bacteria. Use of metal resistance bacterial for the degradation of organic compounds has been widely used bioaugmentation strategy. Along with that use of sorbents/bio sorbents, biosurfactants and phytoremediation approaches have already been well reported. Bioremediation strategy with dual potential to detoxify the Cr(VI) and PCBs would be a probable option for simultaneous biotreatment. Application of bioreactors and biofilms covered organic particles can be utilized as efficient bioaugmentation approach. In this review, biotreatment systems and bacterial oxidative and reductive enzymes/processes are explained and possible biotransformation pathway has been purposed for bioremediation of co-contaminated waters.

Hexavalent chromium reducing bacteria: mechanism of reduction and characteristics

As a common heavy metal, chromium and its compounds are widely used in industrial applications, e.g., leather tanning, electroplating, and in stainless steel, paints and fertilizers. Due to the strong toxicity of Cr(VI), chromium is regarded as a major source of pollution with a serious impact on the environment and biological systems. The disposal of Cr(VI) by biological treatment methods is more favorable than traditional treatment methods because the biological processes are environmentally friendly and cost-efficient. This review describes how bacteria tolerate and reduce Cr(VI) and the effects of some physical and chemical factors on the reduction of Cr(IV). The practical applications for Cr(VI) reduction of bacterial cells are also included in this review.

Bacterial extracellular electron transfer: a powerful route to the green biosynthesis of inorganic nanomaterials for multifunctional applications

Synthesis of inorganic nanomaterials such as metal nanoparticles (MNPs) using various biological entities as smart nanofactories has emerged as one of the foremost scientific endeavors in recent years. The biosynthesis process is environmentally friendly, cost-effective and easy to be scaled up, and can also bring neat features to products such as high dispersity and biocompatibility. However, the biomanufacturing of inorganic nanomaterials is still at the trial-and-error stage due to the lack of understanding for underlying mechanism. Dissimilatory metal reduction bacteria, especially Shewanella and Geobacter species, possess peculiar extracellular electron transfer (EET) features, through which the bacteria can pump electrons out of their cells to drive extracellular reduction reactions, and have thus exhibited distinct advantages in controllable and tailorable fabrication of inorganic nanomaterials including MNPs and graphene. Our aim is to present a critical review of recent state-of-the-art advances in inorganic biosynthesis methodologies based on bacterial EET using Shewanella and Geobacter species as typical strains. We begin with a brief introduction about bacterial EET mechanism, followed by reviewing key examples from literatures that exemplify the powerful activities of EET-enabled biosynthesis routes towards the production of a series of inorganic nanomaterials and place a special emphasis on rationally tailoring the structures and properties of products through the fine control of EET pathways. The application prospects of biogenic nanomaterials are then highlighted in multiple fields of (bio-) energy conversion, remediation of organic pollutants and toxic metals, and biomedicine. A summary and outlook are given with discussion on challenges of bio-manufacturing with well-defined controllability.

Chemical-Assisted Microbially Mediated Chromium (Cr) (VI) Reduction Under the Influence of Various Electron Donors, Redox Mediators, and Other Additives: An Outlook on Enhanced Cr(VI) Removal

Chromium (Cr) (VI) is a well-known toxin to all types of biological organisms. Over the past few decades, many investigators have employed numerous bioprocesses to neutralize the toxic effects of Cr(VI). One of the main process for its treatment is bioreduction into Cr(III). Key to this process is the ability of microbial enzymes, which facilitate the transfer of electrons into the high valence state of the metal that acts as an electron acceptor. Many underlying previous efforts have stressed on the use of different external organic and inorganic substances as electron donors to promote Cr(VI) reduction process by different microorganisms. The use of various redox mediators enabled electron transport facility for extracellular Cr(VI) reduction and accelerated the reaction. Also, many chemicals have employed diverse roles to improve the Cr(VI) reduction process in different microorganisms. The application of aforementioned materials at the contaminated systems has offered a variety of influence on Cr(VI) bioremediation by altering microbial community structures and functions and redox environment. The collective insights suggest that the knowledge of appropriate implementation of suitable nutrients can strongly inspire the Cr(VI) reduction rate and efficiency. However, a comprehensive information on such substances and their roles and biochemical pathways in different microorganisms remains elusive. In this regard, our review sheds light on the contributions of various chemicals as electron donors, redox mediators, cofactors, etc., on microbial Cr(VI) reduction for enhanced treatment practices.

Lead bioaccumulation mediated by Bacillus cereus BPS-9 from an industrial waste contaminated site encoding heavy metal resistant genes and their transporters

This study explores the soil microorganisms for their Lead bioremediation capability. The MIC values of the six Lead resistant bacteria were evaluated, and the AAS studies of these isolates estimated their Lead accumulation percentage. The results showed that the isolate namely Bacillus cereus BPS-9 as identified based on 16S rDNA gene sequences was shown to have the highest Lead accumulation potential (79.26 %) and also selected for bioaccumulation studies. Despite the reduction in growth rate, the superoxide dismutase activity of B. cereus BPS-9 was increased with a rise in the concentration of Lead manifested through increased nitro-blue tetrazolium (NBT) reduction from 3.94 % to 77.48 %. Moreover, the biosorption capacity of B. cereus BPS-9 was 193.93 mg/g and the Langmuir isotherm model showed a value of R² = 0.9. Furthermore, the FTIR analysis also established the role of C-H, C=C, N=N, N-H, and C-O functional groups in Lead adsorption and the SEM micrographs showed that the cells of B. cereus BPS-9 became dense, adhered and distorted after Lead adsorption. Finally, the In-silico results obtained by functional analysis through SEED viewer of the whole genome of B. cereus deciphered the presence of genes encoding heavy metal resistant proteins and transporters for the efflux of heavy metals.

The Genus Ochrobactrum as Major Opportunistic Pathogens

Ochrobactrum species are non-enteric, Gram-negative organisms that are closely related to the genus Brucella. Since the designation of the genus in 1988, several distinct species have now been characterised and implicated as opportunistic pathogens in multiple outbreaks. Here, we examine the genus, its members, diagnostic tools used for identification, data from recent Ochrobactrum whole genome sequencing and the pathogenicity associated with reported Ochrobactrum infections. This review identified 128 instances of Ochrobactrum spp. infections that have been discussed in the literature. These findings indicate that infection review programs should consider investigation of possible Ochrobactrum spp. outbreaks if these bacteria are clinically isolated in more than one patient and that Ochrobactrum spp. are more important pathogens than previously thought.

Improving Biodegradation of Clofibric Acid by Trametes pubescens through the Design of Experimental Tools

Clofibric acid (CLF) is the main pharmacologically active metabolite in composition of the pharmaceutical products used for controlling blood lipid content. This xenobiotic compound is highly persistent in the aquatic environment and passes unchanged or poorly transformed in wastewater treatment plants. A white-rot fungal strain of Trametes pubescens was previously selected, for its ability for clofibric acid biodegradation (up to 30%) during cultivation in submerged system under aerobic conditions at an initial CLF concentration of 15 mg L⁻¹. Plackett-Burman design (PBD) and response surface methodology (RSM) were used for experimental planning, mathematical modelling and statistical analysis of data of the biotechnological process of CLF biotransformation by Trametes pubescens fungal strain. After optimization, the capacity of the selected Trametes pubescens strain to degrade CLF was increased by cultivation in a liquid medium containing 3 g·L⁻¹ yeast extract, 15 g·L⁻¹ peptone, 5 g·L⁻¹ glucose and mineral salts, inoculated at 2% (v/v) vegetative inoculum and cultivated at pH 5.5, during 14 days at 25 °C and 135 rpm. In these optimized biotechnological conditions, the CLF biotransformation yield was 60%.

Modeling and Cr(VI) ion uptake kinetics of Sorghum bicolor plant assisted by plant growth-promoting Pannonibacter phragmetitus: an ecofriendly approach

The research work focuses on the application of Cr(VI)-resistant plant growth-promoting bacteria Pannonibacter phragmetitus for enhancing Cr(VI) uptake by Sorghum bicolor. Significant increase in plant shoot and root characters was found when assisted by P. phragmetitus. The obtained strain showed 700 mg/L of chromium reduction at 24-h incubation. Indole-3 acetic acid (IAA) production by the bacterial strain was found to be 86.45 μg/mL. Pannonibacter phragmetitus solubilized tricalcium phosphate showing maximum solubilizing activity of PSI = 3.31. The q_max of P. phragmetitus was high in the wavelength of 600 nm. Langmuir isotherm best described the Cr(VI) ion uptake by the plant. The R_L values reliably reduced with expanding Cr(VI) ion concentration from 25 to 150 mg/L. The outcomes of kinetic studies showed that compared with pseudo first-order, pseudo second-order kinetics better describes the plant Cr(VI) uptake rate. Elovich model describes the increased rates for attaining equilibrium. The equilibrium parameter values for different Cr(VI) ion concentrations range between 0 and 1 which describes the favorable condition for plant metal uptake at different concentrations. Graphical abstract.

Characterization of novel thorium tolerant Ochrobactrum intermedium AM7 in consort with assessing its EPS-Thorium binding

Currently, radioactive waste is disposed primarily by burial in a deep geological repository. Microorganisms thriving in such contaminated environment show tolerance to radionuclides. In the present study the bacterial flora, from soil sample collected from an area around atomic power station exposed to radionuclides and heavy metals, was cultivated and assessed for thorium (Th) tolerance. Of all the isolates, strain AM7 identified as O. intermedium was selected since it could thrive at high levels of Th (1000 mg L^-1). AM7 was characterized physico-chemically and its culture medium was optimized using central composite design of response surface methodology for assessing its growth properties in presence of Th. The strain also showed exceptional exopolysaccharide (EPS) production and its yield was further analyzed using one factor study to investigate the influence of each medium component. On supplementing the EPS medium with Th, no significant decrease in yield was observed. FTIR spectroscopy revealed the functional groups of EPS involved in EPS-Th binding. To the best of our knowledge, this is the first report showing exceptional Th-tolerance by any bacteria. Such study will help other researchers to strategize an environment-friendly way of radwaste disposal.

Ochrobactrum teleogrylli sp. nov., a pesticide-degrading bacterium isolated from the insect Teleogryllus occipitalis living in deserted cropland

A Gram-stain-negative, non-spore-forming, motile, aerobic, rod-shaped bacteria strain, designated LCB8^T, was isolated from the insect Teleogryllus occipitalis captured from a deserted cropland in Shuangliu district, Chengdu, PR China. Phylogenetic analysis on the basis of 16S rRNA gene sequence indicated that the strain represented a member of the genus Ochrobactrum, family Brucellaceae, class Alphaproteobacteria. Ochrobactrum pecoris CCUG 60088^T (97.9 %) and Ochrobactrum haematophilum CCUG 38531^T (98.8 %) were identified as the most closely related phylogenetic neighbours of strain LCB8^T. The novel strain was able to grow at salt concentrations of 0-4.5 % (w/v), pH 5-9 and temperatures of 20-42 °C. The major quinone system was ubiquinone Q-10, the major fatty acids were C_18 : 1ω7c, C_16 : 0 and C_18 : 0. The major polar lipids were phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, phosphatidylmonomethylethanolamine, diphosphatidylglycerol and four undefined aminolipids. The major polyamines were putrescine and spermidine. Genome sequencing revealed a genome size of 4.76 Mbp and a DNA G+C content of 57.1 mol%. These phenotypic, genotypic and chemotaxonomic traits excellently supported the affiliation of LCB8^T to the genus Ochrobactrum. Pairwise determined whole-genome average nucleotide identity (ANI) values indicated that strain LCB8^T represents a novel species, for which we propose the name Ochrobactrum teleogrylli sp. nov. with the type strain LCB8^T (=KCTC 72031^T=CGMCC 1.13984^T).

Coupling enhancement of Chromium(VI) bioreduction in groundwater by phosphorus minerals

Groundwater contaminated by hexavalent chromium (Cr(VI)) has posed severe threat to the environment and public health. Although heterotrophic bioremediation has been known as an efficient approach, little is explored on mineral nutrient source addition such as phosphorus minerals. In this study, the stabilization and sustainability of phosphorus minerals for providing phosphorus has been investigated, and the enhancement of Cr(VI) removal by mixed bacterial consortium coupled with phosphorus minerals was also observed and further verified, with 1.4-3.9 times K values (first-order) increase under different conditions. We demonstrated that the applied of phosphorus minerals facilitated the reduction of Cr(VI) and the removal of Cr(III), promoted the resistance of Cr(VI) and the generation of antioxidase, and engendered the evolution of microbial community structures and functional genes. These findings provide a new insight for enhancement of Cr(VI)-contaminated groundwater in-situ remediation.

Comparative Analyses of the Microbial Communities Inhabiting Coal Mining Waste Dump and an Adjacent Acid Mine Drainage Creek

Microbial communities inhabiting the acid mine drainage (AMD) have been extensively studied, but the microbial communities in the coal mining waste dump that may generate the AMD are still relatively under-explored. In this study, we characterized the microbial communities within these under-explored extreme habitats and compared with those in the downstream AMD creek. In addition, the interplay between the microbiota and the environmental parameters was statistically investigated. A Random Forest ensemble model indicated that pH was the most important environmental parameter influencing microbial community and diversity. Parameters associated with nitrogen cycling were also critical factors, with positive effects on microbial diversity, while S-related parameters had negative effects. The microbial community analysis also indicated that the microbial assemblage was driven by pH. Various taxa were enriched in different pH ranges: Sulfobacillus was the indicator genus in samples with pH < 3 while Acidobacteriaceae-affiliated bacteria prevailed in samples with 3 < pH < 3.5. The detection of some lineages that are seldom reported in mining areas suggested the coal mining dumps may be a reservoir of phylogenetic novelty. For example, potential nitrogen fixers, autotrophs, and heterotrophs may form diverse communities that actively self-perpetuate pyrite dissolution and acidic waste generation, suggesting unique ecological strategies adopted by these innate microorganisms. In addition, co-occurrence network analyses suggest that members of Acidimicrobiales play important roles in interactions with other taxa, especially Fe- and S-oxidizing bacteria such as Sulfobacillus spp.

Reduction of hexavalent chromium (VI) by indigenous alkaliphilic and halotolerant Microbacterium sp. M5: comparative studies under growth and nongrowth conditions

AIMS

To evaluate hexavalent chromium (Cr (VI)) reduction potential of indigenous isolate M5, under growing and nongrowing conditions.

METHODS AND RESULTS

Microbacterium sp. M5 was isolated from soil samples collected from a common effluent treatment plant, after enrichment of indigenous microbial diversity in the presence of 200 mg l^-1 of Cr (VI). The isolate achieved complete reduction of 400 mg l^-1 Cr (VI) supplement to Luria Bertani medium having initial pH of 9·0 after 48 h incubation. Furthermore, the reduction potential of resting and surfactant treated cell membrane compromised cells of M5 was evaluated. The control and biosurfactant treated cells achieved 22·71 ± 0·5% and 40·56 ± 0·5% reduction of 50 mg l^-1 Cr (VI) in Tris-HCl buffer, under resting cells conditions. To the best of our knowledge, this is the first report where cells with compromised cell membrane obtained after exposure to biosurfactant have been evaluated for Cr (VI) reduction.

CONCLUSION

The Cr (VI) reduction potential of Microbacterium sp. M5 could be effectively exploited for treatment of chromium-rich effluents, under nongrowing conditions.

SIGNIFICANCE AND IMPACT OF THE STUDY

The isolate M5 could be a potential inoculum for effluent treatment plants as it is able to support Cr (VI) reduction under wide range of pH, salinity and in the presence of different metal ions.

Microbial reduction fate of chromium (Cr) in aqueous solution by mixed bacterial consortium

Groundwater contaminated by Cr(VI) requires effective remediation to prevent adverse environmental impacts. The biodegradation of Cr(VI) has been documented for several decades, but little remains known about the removal fate of chromium, including the main species of reductase (sites) and functional genes involved in Cr(VI) reduction in mixed bacterial consortium. Cr(VI) reduction in this study was verified to be an enzyme-mediated process. Meanwhile, Cr(VI) reduction of different cell components demonstrated that the extracellular enzyme was the main active substance, and the distribution of Cr after experiment was quantified using mass balance calculation. Furthermore, the optimal pH for reduction was 8.0, with the reduction rate decreasing with increasing initial Cr(VI) concentrations. The co-existing oxyanions had little effect on Cr(VI) reduction, while the presence of other heavy metals had a relatively significant influence. The evolutionary behavior of microbial community structure and functional genes affected by Cr(VI) were also analyzed, which provided new insights on the underlying mechanisms involved in bioreduction in this study. These results generated new understanding of the reduction mechanisms on the Cr-relevant bacterial species and genes, which would be helpful in designing strategies for the bioremediation of Cr(VI) contaminated water.

Characterization of iron-metabolizing communities in soils contaminated by acid mine drainage from an abandoned coal mine in Southwest China

Acid mine discharge (AMD) has been demonstrated to have significant impacts on microbial community composition in the surrounding soil environment. However, their effect on adjacent soil has not been extensively studied. In this study, microbial community composition of 20 AMD-contaminated soil samples collected from an abandoned coal mine along an AMD creek was characterized using high-throughput sequencing. All samples were characterized as extremely low in pH (< 3) and relatively enriched in HCl-extractable Fe species. The dominant phylotypes were belonging to genera Ochrobactrum, Acidiphilium, Staphylococcus, Brevibacterium, and Corynebacterium. Canonical correspondence analysis results revealed that the HCl-extractable Fe(III) had a strong impact on the soil microbial assemblage. Co-occurrence network analysis revealed that Aquicella, Acidobacteriaceae, Ochrobactrum, Enhydrobacter, Sphingomonas, and Legionellales were actively correlated with other taxa. As expected, most of the abundant taxa have been reported as acidophilic Fe-metabolizing bacteria. Hence, a co-occurring sub-network and a phylogenetic tree related to microbial taxa responsible for Fe metabolism were constructed and described. The biotic interaction showed that Dechloromonas exhibited densely connections with Fe(III)-reducing bacteria of Comamonas, Burkholderia, Shewanella, Stenotrophomonas, Acidithiobacillus, and Pseudomonas. These results demonstrated that Fe-metabolizing bacteria could have an important role in the Fe biogeochemical cycling.

Structural basis for expanding the application of bioligand in metal bioremediation: A review

Bioligands (BL) present in plant and microbes are primarily responsible for their use in metal decontamination. Both primary (proteins and amino acid) and secondary (proliferated) response in the form of BL is possible in plants and microbes toward metal bioremediation. Structure of these BL have specific requirement for preferential binding towards a particular metal in biomass. The aim of this review is to explore various templates from BL (as metal host) for the metal detoxification/decontamination and associated bioremediation. Mechanistic explanation for bioremediation may involve the various processes like: (i) electron transfer; (ii) translocation; and (iii) coordination number variation. HSAB (hard and soft acid and base) concept can act as guiding principle for many such processes. It is possible to investigate various structural homolog of BL (similar to secondary response in living stage) for the possible improvement in bioremediation process.

Chromium tolerance, bioaccumulation and localization in plants: An overview

In the current industrial scenario, chromium (Cr) as a metal is of great importance, but poses a major threat to the environment. Phytoremediation provides an environmentally sustainable, ecofriendly, cost effective approach for environmental cleanup of Cr. This review presents the current status of phytoremediation research with particular emphasis on cleanup of Cr contaminated soil and water systems. It gives a detailed account of the work done by different authors on the Cr bioavailability, uptake pathway, toxicity and storage in plants following the phytoextraction mechanism. This paper also describes recent findings related to Cr localization in hyperaccumulator plants. It gives an insight into the processes and mechanisms that allow plants to remove Cr from contaminated sites under varying conditions. These detailed knowledge of changes in plant metabolic pool in response to Cr stress would immensely help understand and improve the phytoextraction process. Further, this review provides a detailed understanding of Cr uptake and detoxification mechanism by plants that can be applied in developing a suitable approach for a better applicability of the process.

Hexavalent chromium reduction potential of Cellulosimicrobium sp. isolated from common effluent treatment plant of tannery industries

Present study deals with the isolation and characterization of a bacterium capable for the effective reduction of Cr(VI) from tannery wastewater. Based on the 16S rRNA gene sequence analysis, this bacterium was identified as Cellulosimicrobium sp. (KX710177). During the Cr(VI) reduction experiment performed at 50, 100, 200,and 300mg/L of Cr(VI) concentrations, the bacterium showed 99.33% and 96.98% reduction at 50 and 100mg/L at 24 and 96h, respectively. However, at 200 and 300mg/L concentration of Cr(VI), only 84.62% and 62.28% reduction was achieved after 96h, respectively. The SEM analysis revealed that bacterial cells exposed to Cr(VI) showed increased cell size in comparison to unexposed cells, which might be due to either the precipitation or adsorption of reduced Cr(III) on bacterial cells. Further, the Energy Dispersive X-ray (EDX) analysis showed some chromium peaks for cells exposed to Cr(VI), which might be either due to the presence of precipitated reduced Cr(III) on cells or complexation of Cr(III) with cell surface molecules. The bacterium also showed resistance and sensitivity against the tested antibiotics with a wide range of MIC values ranging from 250 to 800mg/L for different heavy metals. Thus, this multi-drug and multi-metal resistant bacterium can be used as a potential agent for the effective bioremediation of metal contaminated sites.

Optimization of chromium and tannic acid bioremediation by Aspergillus niveus using Plackett-Burman design and response surface methodology

A chromium and tannic acid resistance fungal strain was isolated from tannery effluent, and identified as Aspergillus niveus MCC 1318 based on its rDNA gene sequence. The MIC (minimum inhibitory concentration) of the isolate against chromium and tannic acid was found to be 200 ppm and 5% respectively. Optimization of physiochemical parameters for biosorption of chromium and tannic acid degradation was carried out by Plackett-Burman design followed by response surface methodology (RSM). The maximum chromium removal and tannic acid degradation was found to be 92 and 68% respectively by A. niveus. Chromium removal and tannic acid degradation was increased up to 11 and 6% respectively after optimization. Scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) was used to investigate biosorption phenomena.

Copper (II) binding of NAD(P)H- flavin oxidoreductase (NfoR) enhances its Cr (VI)-reducing ability

Microbes can reduce hexavalent chromium Cr (VI) to the less toxic and soluble trivalent Cr (III). Copper stimulates microbial reduction of Cr (VI) by the Bacillus, Ochrobactrum, and Gluconobacter species; however, the mechanism remains unclear. In our study, the rate of Cr (VI) reduction by Staphylococcus aureus LZ-01 was increased by 210 % when supplemented with 60 μM Cu (II). A putative NAD(P)H-flavin oxidoreductase gene (nfoR) was upregulated under Cr (VI) stress. NfoR-knockout mutant displayed impaired reduction of Cr (VI) and Cu (II)-enhanced Cr (VI) reduction by nfoR isogenic mutant was attenuated in the presence of Cu (II). In vitro tests showed an increased V_max value of 25.22 μM min⁻¹ mg⁻¹ NfoR in the presence of Cu (II). Together, these results indicate that NfoR is responsible for Cu (II) enhancement. Isothermal titration calorimetry (ITC) assays confirmed the interaction of NfoR with Cu (II) at the dissociation constant of 85.5 μM. Site-directed mutagenesis indicates that His100, His128, and Met165 residues may be important for Cu (II) binding, while Cys163 is necessary for the FMN binding of NfoR. These findings show that Cu (II)-enhanced NfoR belongs to a new branch of Cr (VI) reductases and profoundly influences Cr (VI) reduction.

Prevalence, Host Range, and Comparative Genomic Analysis of Temperate Ochrobactrum Phages

Ochrobactrum and Brucella are closely related bacteria that populate different habitats and differ in their pathogenic properties. Only little is known about mobile genetic elements in these genera which might be important for survival and virulence. Previous studies on Brucella lysogeny indicated that active phages are rare in this genus. To gain insight into the presence and nature of prophages in Ochrobactrum, temperate phages were isolated from various species and characterized in detail. In silico analyses disclosed numerous prophages in published Ochrobactrum genomes. Induction experiments showed that Ochrobactrum prophages can be induced by various stress factors and that some strains released phage particles even under non-induced conditions. Sixty percent of lysates prepared from 125 strains revealed lytic activity. The host range and DNA similarities of 19 phages belonging to the families Myoviridae, Siphoviridae, or Podoviridae were determined suggesting that they are highly diverse. Some phages showed relationship to the temperate Brucella inopinata phage BiPB01. The genomic sequences of the myovirus POA1180 (41,655 bp) and podovirus POI1126 (60,065 bp) were analyzed. Phage POA1180 is very similar to a prophage recently identified in a Brucella strain isolated from an exotic frog. The POA1180 genome contains genes which may confer resistance to chromate and the ability to take up sulfate. Phage POI1126 is related to podoviruses of Sinorhizobium meliloti (PCB5), Erwinia pyrifoliae (Pep14), and Burkholderia cenocepacia (BcepIL02) and almost identical to an unnamed plasmid of the Ochrobactrum intermedium strain LMG 3301. Further experiments revealed that the POI1126 prophage indeed replicates as an extrachromosomal element. The data demonstrate for the first time that active prophages are common in Ochrobactrum and suggest that atypical brucellae also may be a reservoir for temperate phages.

Optimization of Culture Conditions for Growth Associated with Cr(VI) Removal by Wickerhamomyces anomalus M10

Chromate-resistant microorganisms with the ability of reducing toxic Cr(VI) to less toxic Cr(III), are candidates for bioremediation. An alternative culture medium to reduce Cr(VI) using Wickerhamomyces anomalus M10 was optimized. Using the Plackett-Burman design, it was determined that sucrose, K₂HPO₄ and inoculum size had significant effects on chromate removal (i.e., reduction) at 24 h. Concentrations of these significant factors were adjusted using a complete factorial design. In this case, only the K₂HPO₄ effect was significant at 12 h of culture, with greater Cr(VI) removal at low concentration (1.2 g L^-1). The optimum medium was validated at the fermenter scale level. Optimal culture conditions for complete removal of Cr(VI) (1 mM) were 400 rpm agitation and air flow of 1 vvm. Moreover, W. anomalus M10 completely removed consecutively added pulses of Cr(VI) (1 mM). These results show interesting characteristics from the standpoint of biotechnology because the development of a future remediation process using W. anomalus M10 can represent an efficient and highly profitable technology for removing the toxic form of Cr.

Copper oxide nanoparticles and copper sulphate act as antigenotoxic agents in drosophila melanogaster

The biological reactivity of metal and metal oxide nanomaterials is attributed to their redox properties, which would explain their pro- or anti-cancer properties depending on exposure circumstances. In this sense, copper oxide nanoparticles (CuONP) have been proposed as a potential anti-tumoral agent. The aim of this study was to assess if CuONP can exert antigenotoxic effects using Drosophila melanogaster as an in vivo model. Genotoxicity was induced by two well-known genotoxic compounds, namely potassium dichromate (PD) and ethyl methanesulfonate (EMS). The wing-spot assay and the comet assay were used as biomarkers of genotoxic effects. In addition, changes in the expression of Ogg1 and Sod genes were determined. The effects of CuONP cotreatment were compared with those induced by copper sulfate (CS), an agent releasing copper ions. Using the wing-spot assay, CuONP and CS were not able to reduce the genotoxic effects of EMS exposure, but had the ability to decrease the effects induced by PD, reducing the frequency of mutant twin-spots that arise from mitotic recombination. In addition, CuONP and CS were able to reduce the DNA damage induced by PD as determined by the comet assay. In general, similar qualitative antigenotoxic effects were obtained with both copper compounds. The antigenotoxic effects of environmentally relevant and non-toxic doses of CuONP and CS may be explained by their ability to partially restore the expression levels of the repair gene Ogg1 and the antioxidant gene Cu,ZnSod, both of which are inhibited by PD treatment. Environ. Mol. Mutagen. 58:46-55, 2017. © 2016 Wiley Periodicals, Inc.

Genotoxicity evaluation of tannery effluent treated with newly isolated hexavalent chromium reducing Bacillus cereus

In this study, the efficiency of free and immobilized cells of newly isolated hexavalent chromium [Cr(VI)] reducing Bacillus cereus strain Cr1 (accession no. KJ162160) was studied in the treatment of tannery effluent. The analysis of effluents revealed high chemical oxygen demand (COD-1260 mg/L), biological oxygen demand (BOD5-660 mg/L), total dissolved solids (TDS-14000 mg/L), electrical conductivity (EC-21.5 mS/cm) and total chromium (TC-2.4 mg/L). The effluents also showed genotoxic effects to Allium cepa. Treatment of tannery effluent with isolated B. cereus strain led to considerable reduction of pollutant load. The pollutant load reduction was studied with both immobilized and free cells and immobilized cells were more effective in reducing COD (65%), BOD (80%), TDS (67%), EC (65%) and TC (92%) after 48 h. GC-MS analysis of pre and post-treatment tannery effluent samples revealed reduction of organic load after treatment with free and immobilized cells. An improvement in mitotic index and reduction in chromosomal aberrations was also observed in A. cepa grown with post-treatement effluent samples compared to untreated sample. Results demonstrate that both methods of bacterial treatment (free and immobilized) were efficient in reducing the pollutant load of tannery effluent as well as in reducing genotoxic effects, however, treatment with immobilized cells was more effective.

Feather degradation potential of Stenotrophomonas maltophilia KB13 and feather protein hydrolysate (FPH) mediated reduction of hexavalent chromium

An efficient keratinolytic strain of Stenorophomonas maltophilia KB13 was isolated from feather disposal site of Bilaspur, Chhattisgarh, India. The strain could metabolize 10 g/l chicken feathers as sole source of carbon and nitrogen. Soluble protein, amino acid, and cysteine content were found to be maximum (690.6 ± 8.7, 688.9 ± 9.12 and 21 ± 0.36 µg/ml, respectively) at late logarithmic phase of growth. Protease and keratinase activity reached its maximum level (103.26 ± 7.09 and 178.5 ± 9.10 U/ml) at the 4th day of incubation. The feather protein hydrolysate (FPH) obtained after degradation of chicken feathers was utilized to reduce hexavalent chromium. About 78.4 ± 2.4 and 63.6 ± 2.2 % reduction of 50 and 100 mg/l Cr(VI), respectively, was observed after 60 min of incubation with FPH. Further, there was no effect of autoclaved FPH on Cr(VI) reduction indicating that any bacterial enzyme was not involved in reduction process. Cr(VI) reduction was significantly inhibited by 10 mm Hg²⁺ ions indicating the role of sulfur-containing amino acids in reduction process. FTIR analysis confirmed that chromium reduction occurred due to oxidation of amino acids cysteine and cystine. This study shows that FPH arising after feather degradation can be employed as a potential candidate for the reduction of hexavalant chromium.

Characterization of Cu(II) and Cd(II) resistance mechanisms in Sphingobium sp. PHE-SPH and Ochrobactrum sp. PHE-OCH and their potential application in the bioremediation of heavy metal-phenanthrene co-contaminated sites

Soil that is co-contaminated with heavy metals (HMs) and polycyclic aromatic hydrocarbons (PAHs) is difficult to bioremediate due to the ability of toxic metals to inhibit PAH degradation by bacteria. We demonstrated the resistance mechanisms to Cu(II) and Cd(II) of two newly isolated strains of Sphingobium sp. PHE-SPH and Ochrobactrum sp. PHE-OCH and further tested their potential application in the bioremediation of HM-phenanthrene (PhA) co-contaminated sites. The PHE-SPH and PHE-OCH strains tolerated 4.63 and 4.34 mM Cu(II) and also showed tolerance to 0.48 and 1.52 mM Cd(II), respectively. Diverse resistance patterns were detected between the two strains. In PHE-OCH cells, the maximum accumulation of Cu(II) occurred in the cell wall, while the maximum accumulation was in the cytoplasm of PHE-SPH cells. This resulted in a sudden suppression of growth in PHE-OCH and a gradual inhibition in PHE-SPH as the concentration of Cu(II) increased. Organic acid production was markedly higher in PHE-OCH than in PHE-SPH, which may also have a role in the resistance mechanisms, and contributes to the higher Cd(II) tolerance of PHE-OCH. The factors involved in the absorption of Cu(II) or Cd(II) in PHE-SPH and PHE-OCH were identified as proteins and carbohydrates by Fourier transform infrared (FT-IR) spectroscopy. Furthermore, both strains showed the ability to efficiently degrade PhA and maintained this high degradation efficiency under HM stress. The high tolerance to HMs and the PhA degradation capacity make Sphingobium sp. PHE-SPH and Ochrobactrum sp. PHE-OCH excellent candidate organisms for the bioremediation of HM-PhA co-contaminated sites.

Bioremediation of hexavalent chromate using permeabilized Brevibacterium sp. and Stenotrophomonas sp. cells

Bioremediation has been found to be a useful method for removing hexavalent chromium (Cr(VI)), which is very toxic, from wastewater. Two strains of bacteria that were able to reduce Cr(VI) effectively were isolated from Cr(VI) contaminated soil samples and identified as Brevibacterium sp. K1 and Stenotrophomonas sp. D6, respectively, based on 16S rRNA gene sequence analyses. Brevibacterium sp. K1 and Stenotrophomonas sp. D6 could grow in Luria-Broth medium containing K2Cr2O7 at 1000 and 1600 mg/L, respectively, and they completely reduced the Cr(VI) in LB medium containing K2Cr2O7 at 200 mg/L within 72 h. Further analyses revealed that permeabilized K1 and D6 cells reduced Cr(VI) more effectively than did the resting cells. Triton X-100 was the best permeabilizing agent that was tested. The permeabilized cells of both strains could completely reduce Cr(VI) in industrial wastewater twice before needing to be replenished. The results suggested that these chromate-reducing bacteria are potential candidates for practical use biotreating industrial effluents containing Cr(VI) with Stenotrophomonas sp. D6 being the more effective bacterium.

Role of Geitlerinema sp. DE2011 and Scenedesmus sp. DE2009 as Bioindicators and Immobilizers of Chromium in a Contaminated Natural Environment

The aim of this work was to study the potential of the two phototrophic microorganisms, both isolated from Ebro Delta microbial mats, to be used as bioindicators and immobilizers of chromium. The results obtained indicated that (i) the Minimum Metal Concentration (MMC) significantly affecting Chlorophyll a intensity in Geitlerinema sp. DE2011 and Scenedesmus sp. DE2009 was 0.25 µM and 0.75 µM, respectively, these values being lower than those established by current legislation, and (ii) Scenedesmus sp. DE2009 was able to immobilize chromium externally in extracellular polymeric substances (EPS) and intracellularly in polyphosphate (PP) inclusions. Additionally, this microorganism maintained high viability, including at 500 µM. Based on these results, we postulate that Geitlerinema sp. DE2011 and Scenedesmus sp. DE2009 are good chromium-indicators of cytotoxicity and, further, that Scenedesmus sp. DE2009 plays an important role in immobilizing this metal in a contaminated natural environment.