BIOSORPTION OF CD, CR, MN, AND PB FROM AQUEOUS SOLUTIONS BY Bacillus SP STRAINS ISOLATED FROM INDUSTRIAL WASTE ACTIVATE SLUDGE

Biosorption of chromium by live and dead cells of Bacillus nitratireducens isolated from textile effluent

Bacillus nitratireducens was isolated from textile effluent and showed high tolerance to chromium (Cr), reaching up to a 1000 mg/L MIC value. This research was aimed at utilizing biosorbents from live and dead cells of B. nitratireducens to remove Cr from an aqueous solution. A batch biosorption test was performed, and mechanisms analysis was approached by an adsorption-desorption test, SEM-EDS, and FTIR analysis. Cr removal by dead cells in 25, 50, and 100 mg/L of Cr were 58.99 ± 0.7%, 69.8 ± 0.2%, and 82.87 ± 0.11%, respectively, while that by live cells was 73.08 ± 1.9%, 80.27 ± 6.33%, and 86.17 ± 1.93%, respectively. Live cells showed significantly higher Cr removal and adsorption capacities as compared to dead cells. In all concentrations, absorption contributed more than adsorption to the Cr removal by both live and dead cells. Absorption of Cr was subjected to occur due to passive mechanisms in dead cells while involving some active mechanisms in live cells. SEM-EDS confirmed the detection of Cr on the cell surface, while FTIR revealed the shifting of some peaks after the biosorption test, suggesting interactions between Cr and functional groups. Further TEM analysis is suggested to be conducted as a future approach to reveal the inner structure of cells and confirm the involvement of absorption mechanisms.

Deciphering the mechanistic role of Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52) in bio-sorption and phyto-assimilation of Cadmium via Linum usitatissimum L. Seedlings

Three Cd2+ resistant bacterium's minimal inhibition concentrations were assessed and their percentages of Cd2+ accumulation were determined by measurements using an atomic absorption spectrophotometer (AAS). The results revealed that two isolates Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52), identified by 16S rDNA gene sequencing, showed a higher percentage of Cd2+ accumulation i.e., 83.78% and 81.79%, respectively. Moreover, both novel strains can tolerate Cd2+ levels up to 2000 mg/L isolated from district Chakwal. Amplification of the czcD, nifH, and acdS genes was also performed. Batch bio-sorption studies revealed that at pH 7.0, 1 g/L of biomass, and an initial 150 mg/L Cd2+ concentration were the ideal bio-sorption conditions for Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52). The experimental data were fit to Langmuir isotherm measurements and Freundlich isotherm model R2 values of 0.999 for each of these strains. Bio sorption processes showed pseudo-second-order kinetics. The intra-diffusion model showed Xi values for Bacillus paramycoides (PM51) and Bacillus tequilensis (PM52) of 2.26 and 2.23, respectively. Different surface ligands, was investigated through Fourier-transformation infrared spectroscopy (FTIR). The scanning electron microscope SEM images revealed that after Cd2+ adsorption, the cells of both strains became thick, adherent, and deformed. Additionally, both enhanced Linum usitatissimum plant seed germination under varied concentrations of Cd2+ (0 mg/L, 250 mg/L,350 mg/L, and 500 mg/L). Current findings suggest that the selected strains can be used as a sustainable part of bioremediation techniques.

Assessment of Iron Biosorption Potential by Live and Dead Biomass of Bacillus subtilis (MN093305) from Aqueous Solution

Heavy metals polluted aquatic ecosystems and become a global environmental issue due to their toxic effect on all forms of ecosystems and further on all forms of life. Heavy metals are non- degradable and accumulated in different life forms by accumulating in the food chain; this increases the need for the development of a sustainable method for the removal of these metals. Biosorption is an eco-friendly and cost-effective convenient technique of heavy metal bioremediation from the contaminated aquatic ecosystem. The current investigation involves biosorption of iron using Bacillus subtilis strain (MN093305) isolated from Ganga river at different physical parameters with the highest rate of biosorption was 96.64%, 98.91%, 97.88%, and 99.44% at pH 5, 60 min incubation period, 35 °C temperature and 2.5 mg/ml of biomass respectively for dead biomass. Living biomass biosorption rate was 87.32%, 96.74%, 96.94% and 95.02% at pH 7, 72 h, 35 °C and 2.5 mg/ml respectively. Functional groups involved in the biosorption of iron by Bacillus subtilis were fitted to a second-order kinetic model. Langmuir and Freundlich's isotherm are used to evaluate data; both isotherms indicate iron absorption as a favorable process.

A facile-treated sago bark (Metroxylon sagu) as a biosorbent for Cd(II) ions removal in aqueous solution by using the batch method

The performance of sago bark for Cd(II) ions removal in the aqueous solution has been investigated using the batch method. The sago bark was facile-treated using HNO3 0.01 M and its ability on Cd(II) removal was evaluated under specific parameters such as pH, contact time, agitation speed, temperature, initial concentration, and adsorbent mass. The adsorption capacity of sago bark was found to be 2.473 mg/g. The Langmuir isotherm model corresponding to the monolayer adsorption process described the adsorption data well. The kinetic and thermodynamic evaluation confirmed that the Cd(II) ion sorption followed a pseudo-second-order model and endothermic. The adsorption capacity decreased after three times adsorption-desorption cycles. This result showed that the treated sago bark could be a good candidate as an adsorbent for Cd(II) removal.

Environmental sporobiota: Occurrence, dissemination, and risks

Spore-forming bacteria known as sporobiota are widespread in diverse environments from terrestrial and aquatic habitats to industrial and healthcare systems. Studies on sporobiota have been mainly focused on food processing and clinical fields, while a large amount of sporobiota exist in natural environments. Due to their persistence and capabilities of transmitting virulence factors and antibiotic resistant genes, environmental sporobiota could pose significant health risks to humans. These risks could increase as global warming and environmental pollution has altered the life cycle of sporobiota. This review summarizes the current knowledge of environmental sporobiota, including their occurrence, characteristics, and functions. An interaction network among clinical-, food-related, and environment-related sporobiota is constructed. Recent and effective methods for detecting and disinfecting environmental sporobiota are also discussed. Key problems and future research needs for better understanding and reducing the risks of environmental sporobiota and sporobiome are proposed.

Prospects of Biogenic Xanthan and Gellan in Removal of Heavy Metals from Contaminated Waters

Biosorption is considered an effective technique for the treatment of heavy-metal-bearing wastewaters. In recent years, various biogenic products, including native and functionalized biopolymers, have been successfully employed in technologies aiming for the environmentally sustainable immobilization and removal of heavy metals at contaminated sites, including two commercially available heteropolysaccharides-xanthan and gellan. As biodegradable and non-toxic fermentation products, xanthan and gellan have been successfully tested in various remediation techniques. Here, to highlight their prospects as green adsorbents for water decontamination, we have reviewed their biosynthesis machinery and chemical properties that are linked to their sorptive interactions, as well as their actual performance in the remediation of heavy metal contaminated waters. Their sorptive performance in native and modified forms is promising; thus, both xanthan and gellan are emerging as new green-based materials for the cost-effective and efficient remediation of heavy metal-contaminated waters.

Recent advances in soil remediation technology for heavy metal contaminated sites: A critical review

With the increasing development of industry and urbanization, heavy metal contaminated sites have become progressively conspicuous, particularly by unreasonable emissions from electroplating, nonferrous metals smelting, mine tailing, etc. In recent years, soil remediation technologies for heavy metal contaminated sites have developed rapidly. New and effective remediation technologies have emerged successively, and more successful practical applications have appeared. Therefore, systematical summarization of the current progress is essential. As a result, in this paper, some mainstream soil remediation technologies for heavy metal contaminated sites, including physical remediation (soil thermal desorption and soil replacement), bioremediation (phytoremediation and microbial remediation), chemical remediation (chemical leaching, chemical stabilization, electrokinetic remediation-permeable reactive barrier, and chemical oxidation/reduction), as well as various combined remediation are comprehensively reviewed. The influencing factors, advantages, disadvantages, remediation mechanism, and practical applications are also deeply discussed. Besides, the corresponding remediation strategies are put forward for the remediation of heavily polluted sites such as the chemical industry, smelting, and tailing areas. Overall, this review will be beneficial for the in-depth understanding and provide references for the reasonable selection and development of soil remediation technology for heavy metal contaminated sites.

Practical limitations of bioaugmentation in treating heavy metal contaminated soil and role of plant growth promoting bacteria in phytoremediation as a promising alternative approach

Bioaugmentation, the addition of cultured microorganisms to enhance the currently existing microbial community, is an option to remediate contaminated areas. Several studies reported the success of the bioaugmentation method in treating heavy metal contaminated soil, but concerns related to the applicability of this method in real-scale application were raised. A comprehensive analysis of the mechanisms of heavy metal treatment by microbes (especially bacteria) and the concerns related to the possible application in the real scale were juxtaposed to show the weakness of the claim. This review proposes the use of bioaugmentation-assisted phytoremediation in treating heavy metal contaminated soil. The performance of bioaugmentation-assisted phytoremediation in treating heavy metal contaminated soil as well as the mechanisms of removal and interactions between plants and microbes are also discussed in detail. Bioaugmentation-assisted phytoremediation shows greater efficiencies and performs complete metal removal from soil compared with only bioaugmentation. Research related to selection of hyperaccumulator species, potential microbial species, analysis of interaction mechanisms, and potential usage of treating plant biomass after treatment are suggested as future research directions to enhance this currently proposed topic.

Potential application of thermophilic bacterium Aeribacillus pallidus MRP280 for lead removal from aqueous solution

Bacteria used for application of lead (Pb) removal is usually kept under suboptimal growth conditions. Certain application of Pb removal may be carried out under different condition, such as under aqueous and high temperature conditions. It is, therefore, of interest to examine the Pb removal capacity of the bacteria under adverse environmental conditions. In the present study, Aeribacillus pallidus MRP280, a lead-tolerant thermophilic bacterium was used as an absorbent for the removal of Pb from aqueous solution. The Pb removal and uptake capacity of living and non-living bacterial cells of A. pallidus MRP280 was investigated in 100 mg/L Pb solution. The optimum condition was examined based on several analytical parameters, including temperature, pH, contact time, and cell density. Biosorbent analysis and characterization was carried out using Fourier Transform Infrared (FT-IR) spectroscopy, Scanning Electron Microscope (SEM)-Energy Dispersive X-ray (EDX), and Transmission Electron Microscope (TEM). The results showed that the maximum Pb removal of 96.78 ± 0.19% and 88.64 ± 0.60% were obtained using living and non-living biomass, respectively at 55 °C, pH 6, OD₆₀₀0.5 for 100 min. Meanwhile, the maximum uptake capacity of 86.47 ± 1.32 mg/g and 85.31 ± 1.37 mg/g by living and non-living cells was reached at 55 °C, pH 6, OD₆₀₀0.25 for 60 min. Moreover, Pb removing activity was facilitated by the biosorption and bioaccumulation process. Overall, it is shown that A. pallidus MRP280 is effective when applied as biosorbent in removing Pb from contaminated wastewater at high temperatures.

Enhanced simultaneous adsorption of As(iii), Cd(ii), Pb(ii) and Cr(vi) ions from aqueous solution using cassava root husk-derived biochar loaded with ZnO nanoparticles

This study presents the modification of cassava root husk-derived biochar (CRHB) with ZnO nanoparticles (ZnO-NPs) for the simultaneous adsorption of As(iii), Cd(ii), Pb(ii) and Cr(vi). By conducting batch-mode experiments, it was concluded that 3% w/w was the best impregnation ratio for the modification of CRHB using ZnO-NPs, and was denoted as CRHB-ZnO3 in this study. The optimal conditions for heavy metal adsorption were obtained at a pH of 6–7, contact time of 60 min, and initial metal concentration of 80 mg L⁻¹. The heavy metal adsorption capacities onto CRHB-ZnO3 showed the following tendency: Pb(ii) > Cd(ii) > As(iii) > Cr(vi). The total optimal adsorption capacity achieved in the adsorption of the 4 abovementioned metals reached 115.11 and 154.21 mg g⁻¹ for CRHB and CRHB-ZnO3, respectively. For each Pb(ii), Cd(ii), As(iii), and Cr(vi) metal, the maximum adsorption capacities of CRHB-ZnO3 were 44.27, 42.05, 39.52, and 28.37 mg g⁻¹, respectively, and those of CRHB were 34.47, 32.33, 26.42 and 21.89 mg g⁻¹, respectively. In terms of kinetics, both the pseudo-first-order and the pseudo-second-order fit well with metal adsorption onto biochars with a high correlation coefficient of R², while the best isothermal description followed the Langmuir model. As a result, the adsorption process of heavy metals onto biochars was chemisorption on homogeneous monolayers, which was mainly controlled by cation exchange and surface precipitation mechanisms due to enriched oxygen-containing surface groups with ZnO-NP modification of biochar. The FTIR and EDS analysis data confirmed the important role of oxygen-containing surface groups, which significantly contributed to removal of heavy metals with extremely high adsorption capacities, comparable with other studies. In conclusion, due to very high adsorption capacities for metal cations, the cassava root husk-derived biochar modified with ZnO-NPs can be applied as the alternative, inexpensive, non-toxic and highly effective adsorbent in the removal of various toxic cations.

This study presents the modification of cassava root husk-derived biochar (CRHB) with ZnO nanoparticles (ZnO-NPs) for the simultaneous adsorption of As(iii), Cd(ii), Pb(ii) and Cr(vi).

A meta-analysis of metal biosorption by suspended bacteria from three phyla

Biosorption of heavy metals by bacterial biomass has been the subject of significant research interest in last decades due to its efficiency, relatively low cost and minimal negative effects for the surrounding environment. In this meta-analysis, the biosorption efficiencies of different bacterial strains for Cu(II), Cd(II), Zn(II), Cr(III), Mn(II), Pb(II) and Ni(II) were evaluated. Optimum conditions for the biosorption process such as initial metal concentration, temperature, pH, contact time, metal type, biomass dosage and bacterial phyla, were evaluated for each heavy metal. According to the results, the efficiencies of bacterial biomass for removal of heavy metal were as follows: Cd(II) > Cr(III) > Pb(II) > Zn(II) > Cu(II) > Ni(II) > Mn(II). Firmicute phyla showed the highest overall (living and dead) biosorption efficiency for heavy metals. Living biomass of Proteobacteria had the best biosorption performance. Living bacterial biomass was significantly more efficient in biosorption of Cu(II), Zn(II) and Pb(II) than dead biomass. The maximum biosorption efficiency of bacterial strains for Cd(II), Pb(II) and Zn(II) was achieved at pH values between 6 and 7.5. High temperatures (>35 °C) reduced the removal efficiencies for Cu(II) and Zn(II) and increased the efficiencies for Cd(II) and Cr(III) ions. The maximum biosorption efficiency of non-essential heavy metals occurred with short contact times (<2 h). Essential metals such as Zn and Cu were more efficiently removed with long biosorption durations (>24 h). The mean biosorption capacity of bacterial biomass was between 71.26 and 125.88 mg g^-1. No publication bias existed according to Egger's and Begg's test results.

Application of Mussell-derived biosorbent to remove NH4+ from aqueous solution: Equilibrium and Kinetics

Mussel shells are often considered an abundant waste with no use. This study shows that the employment of mussel shells as a biosorbent for ammonium from water environment is completely possible. By using batch experimental method, optimal conditions for the ammonium adsorption onto mussel shells were determined. Specifically, those include a pH level of 8, contact time of 90 min, an initial ammonium concentration of 40 mg/l and the adsorbent dose of 700 mg/25 ml. With such operating conditions, experiments in laboratory aqueous solutions resulted in a maximum adsorption capacity of 2.33 mg/g, corresponded by 46.575% of efficiency. Adsorption isotherms and kinetics were well described with the Freundlich isothermal model, suggesting a heterogeneous adsorption process occurring on multilayers and both the pseudo-first-order and the pseudo-second-order, implying that the operational fundament was based on chemisorption. Analyses regarding SEM, EDS and FTIR were also implemented to identify the morphology, composition and functional groups of the adsorbent.

Transcription profiling-guided remodeling of sulfur metabolism in synthetic bacteria for efficiently capturing heavy metals

Heavy metal contamination is becoming a global problem threatening human health. Heavy metal removal by engineered microbes by cellular adsorption and uptake is a promising strategy for treatment of heavy metal contamination. However, this strategy is confronted with limited heavy metal-capturing elements. In this study, we performed a transcription profiling-guided strategy for construction of heavy metal-capturing synthetic bacteria. Transcription profiling of a heavy metal-tolerating Cupriavidus taiwanensis strain revealed up-regulation of sulfur metabolism-related operons (e.g., iscSAU and moaEDAB) by Pb²⁺ and Cd²⁺. A synthetic Escherichia coli strain, EcSSMO, was constructed by design of a synthetic sulfur metabolism operon (SSMO) based on iscSAU/moaEDAB. Biochemical analysis and X-ray photoelectron spectroscopy (XPS) revealed that the synthetic bacteria had remodeled sulfur metabolism and enhanced heavy metal-tolerating capacity, with higher surviving EcSSMO cells than the surviving control cells Ec0 (not containing SSMO) at 50 mg/L of Pb²⁺ and Cd²⁺ (>92 % versus <10 %). Moreover, EcSSMO exhibited much higher heavy metal-capturing capacity than Ec0, removing>90 % of Pb²⁺ and Cd²⁺ at 5 mg/L of Pb²⁺ and Cd²⁺, and >40 % of both heavy metals even at 50 mg/L of Pb²⁺ and Cd²⁺. This study reveals emphasizes feasibility of transcription profiling-guided construction of synthetic organisms by large-scale remodeling metabolic network.

A High Manganese-Tolerant Pseudomonas sp. Strain Isolated from Metallurgical Waste Heap Can Be a Tool for Enhancing Manganese Removal from Contaminated Soil

Manganese (Mn) is widely used in industry. However, its extensive applications have generated a great amount of manganese waste, which has become an ecological problem and has led to a decrease in natural resources. The use of microorganisms capable of accumulating Mn ions from contaminated ecosystems offers a potential alternative for the removal and recovery of this metal. The main aim of this work was an investigation of removal potential of Mn from soil by isolated bacterial. For this purpose, eleven bacterial strains were isolated from the soil from metallurgical waste heap in Upper Silesia, Poland. Strain named 2De with the highest Mn removal potential was selected and characterized taking into account its ability for Mn sorption and bioaccumulation from soil and medium containing manganese dioxide. Moreover, the protein profile of 2De strain before and after exposition to Mn was analyzed using SDS/PAGE technique. The 2De strain was identified as a Pseudomonas sp. The results revealed that this strain has an ability to grow at high Mn concentration and possesses an enhanced ability to remove it from the solution enriched with the soil or manganese dioxide via a biosorption mechanism. Moreover, changes in cellular protein expression of the isolated strain were observed. This study demonstrated that autochthonous 2De strain can be an effective tool to remove and recover Mn from contaminated soil.

Novel application of maghemite nanoparticles coated bacteria for the removal of cadmium from aqueous solution

Heavy metals are classified as persistent pollutants owing to their nature of bioaccumulation and affect human life and environment, even in minor concentrations. Divalent Cadmium (Cd²⁺) is one of the heavy metal pollutants that are highly toxic. The present study investigates the novel application of maghemite nanoparticles coated Bacillus subtilis for the removal of Cd²⁺ ions from its aqueous solution by batch adsorption studies. Surface characterization of the biosorbent done by Scanning Electron Microscope (SEM) and the presence of maghemite nanoparticle coat was confirmed. Parameters like pH, initial metal ion concentration, contact time, and temperature that affect the biosorption of cadmium ions are analyzed, and the equilibrium adsorption capacity expressed as a function of each of the parameters. The mechanism of biosorption was studied by plotting adsorption isotherms, and it follows pseudo-second-order kinetics. Thermodynamic studies showed the process to be spontaneous and endothermic. At optimum conditions of pH 4, 30 °C, 120 rpm, maximum removal percentage of 83.5%, which accounts for an equilibrium adsorption capacity of 32.6 mg/g of biosorbent. There was a recovery of 76.4% of the biosorbent after adsorption studies. Based on the adsorptive capacity and good recovery of the biosorbent, maghemite coated Bacillus subtilis proves to be an efficient adsorbent for the removal of Cd²⁺ ions from its aqueous solution.

Structural Changes of Bacillus subtilis Biomass on Biosorption of Iron (II) from Aqueous Solutions: Isotherm and Kinetic Studies

Various microbial biomasses have been employed as biosorbents. Bacterial biomass has added advantages because of easy in production at a low cost. The study investigated the biosorption of iron from aqueous solutions by Bacillus subtilis. An optimum biosorption capacity of 7.25 mg of the metal per gram of the biosorbent was obtained by the Inductive Coupled Plasma Optical Emission Spectroscopy (ICP-OES) under the experimental conditions of initial metal concentration of 100 mg/l, pH 4.5, and biomass dose of 1 g/l at 30°C for 24 hrs. The data showed the best fit with the Freundlich isotherm model while following pseudo-first-order kinetics. Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) analysis confirmed iron biosorption as precipitates on the bacterial surface, and as a peak in the EDX spectrum. The functional hydroxyl, carboxyl, and amino groups that are involved in biosorption were revealed by the Fourier Transform Infrared spectroscopy (FTIR). The amorphous nature of the biosorbent for biosorption was indicated by the X-ray Diffraction (XRD) analysis. The biomass of B. subtilis exhibited a point zero charge (pH_pzc) at 2.0.

Various microbial biomasses have been employed as biosorbents. Bacterial biomass has added advantages because of easy in production at a low cost. The study investigated the biosorption of iron from aqueous solutions by Bacillus subtilis. An optimum biosorption capacity of 7.25 mg of the metal per gram of the biosorbent was obtained by the Inductive Coupled Plasma Optical Emission Spectroscopy (ICP-OES) under the experimental conditions of initial metal concentration of 100 mg/l, pH 4.5, and biomass dose of 1 g/l at 30°C for 24 hrs. The data showed the best fit with the Freundlich isotherm model while following pseudo-first-order kinetics. Scanning Electron Microscope (SEM) and Energy Dispersive X-ray (EDX) analysis confirmed iron biosorption as precipitates on the bacterial surface, and as a peak in the EDX spectrum. The functional hydroxyl, carboxyl, and amino groups that are involved in biosorption were revealed by the Fourier Transform Infrared spectroscopy (FTIR). The amorphous nature of the biosorbent for biosorption was indicated by the X-ray Diffraction (XRD) analysis. The biomass of B. subtilis exhibited a point zero charge (pH_pzc) at 2.0.

Adhesion abilities and biosorption of Cd and Mg by microorganisms - first step for eco-friendly beneficiation of phosphate ore

Chemical reagents used in traditional mineral processing can be toxic and hazardous for the environment. Therefore, the use of biotechnological methods is becoming increasingly important. Great hopes are being placed in the use of microorganisms for bio-beneficiation of raw materials. However, assessment of adhesion abilities of bacteria onto minerals surface as well as biosorption of metals are essential steps before designing final process of each ore beneficiation. The main aim of this work was an investigation of biosorption of Cd and Mg, as well as adhesion abilities of five microorganism species with minerals included in the natural mixture of phosphate ore form Djebel Onk, Algeria. The ore, due to its unique composition, created conditions for adhesion of all five tested microbial strains onto apatite surface during incubation at pH 3. Moreover, Rhodococcus erythropolis CD 130, Pseudomonas fluorescens and Escherichia coli adhered distinctly onto apatite surface during incubation at pH 7. Incubation lasting 20 min at pH 4-6 created the most favorable conditions for biosorption of metals by B. subtilis and adhesion of cells. In case of C. albicans, biosorption of metals as well as adhesion of cells onto the mineral surface were more effective after longer time and in a wider pH range.

Potential use of Bacillus genera for metals removal from spent catalysts

The aim of the present study was to isolate microorganisms able to tolerate Ni²⁺ and V⁵⁺ from different sites located close to a mineral mine in Guanajuato, Mexico, and then to evaluate their ability to remove metals contained in a spent catalyst. Seventeen isolates were obtained; among them seven presented a minimum inhibitory concentration (MIC) higher than 200 mg/L of Ni²⁺ and V⁵⁺ each. Nickel and Vanadium removal was evaluated in 9 K liquid medium added with spent catalyst at 16% (s/v) pulp density and incubated at 30 °C, 150 rpm for 7 days. Only three isolates which were coded as PRGSd-MS-2, MNSH2-AH-3, and MNSS-AH-4 showed a significant removal at the end of treatment corresponding in mg kg^-1 (or percentage metal removal) of 138 (32%), 123 (29%), and 101 (24%) for Ni, respectively; and 557 (26%), 737 (34%), and 456 (21%) mg kg^-1 for V, respectively. The same isolates were capable to remove also Al, Fe, As, and Mg at different extent. Cell morphology changes were observed, in comparison to the control system at the end of biological treatment as a higher quantity of spores for MNSH2-AH-3, 2 μm cells in pairs for MNSS-AH-4, also long chain-vegetative cells having inclusions into the cell surface were observed for PRGSd-MS-2. The three isolated microorganisms were identified by sequencing of the 16S gene as Bacillus thuringiensis, Bacillus megaterium, and Bacillus sp, respectively, suggesting its potential use in the treatment of this solid industrial waste.

Chromate detoxification potential of Staphylococcus sp. isolates from an estuary

Chromium (Cr) pollution is an emerging environmental problem. The present study was carried out to isolate Cr-resistant bacteria and characterize their Cr detoxification and resistance ability. Bacteria screened by exposure to chromate (Cr⁶⁺) were isolated from Mandovi estuary Goa, India. Two isolates expressed high resistance to Cr⁶⁺ (MIC ≥ 300 µg mL^-1), Cr³⁺ (MIC ≥ 900 µg mL^-1), other toxic heavy metals and displayed a pattern of resistance to cephalosporins and ß-lactams. Biochemical and 16 S rRNA gene sequence analysis indicated that both isolates tested belonged to the Staphylococcus genus and were closely related to S. saprophyticus and S. arlettae. Designated as strains NIOER176 and NIOER324, batch experiments demonstrated that both removed 100% of 20 and 50 µg mL^-1 Cr⁶⁺ within 4 and 10 days, respectively. The rate of reduction in both peaked at 0.260 µg mL^-1 h^-1. ATP-binding cassette (ABC) transporter gene involved in transport of a variety of substrates including efflux of toxicants was present in strain NIOER176. Through SDS-PAGE analysis, whole-cell proteins extracted from both strains indicated chromium-induced specific induction and up-regulation of 24 and 40 kDa proteins. Since bacterial ability to ameliorate Cr⁶⁺ is of practical significance, these findings demonstrate strong potential of some estuarine bacteria to detoxify Cr⁶⁺ even when its concentrations far exceed the concentrations reported from many hazardous effluents and chromium contaminated natural habitats. Such potential of salt tolerant bacteria would help in Cr⁶⁺ bioremediation efforts.

Metal removal and morphological changes of B. megaterium in the presence of a spent catalyst

Spent catalysts represent an environmental concern, mainly due to their elevated metal content. Although conventional treatment methods for spent catalysts are available, they generate large volumes of potentially harmful wastes and gaseous emissions. To overcome the environmental impact, biotechnological approaches are currently being explored and developed. Thus, the current study assayed the capability of Bacillus megaterium strain MNSH1-9K-1 to remove Al, Ni, V and Ti contained in the spent catalyst coded as ECAT-TL-II. To this end, B. megaterium MNSH1-9K-1 growth and metal uptake abilities in the presence of ECAT-TL-II spent catalyst at 15% (wt/vol) pulp density were evaluated in modified Starkey medium at 37 °C and 200 rpm. The results presented here show B. megaterium resistance capability to the high-metal content residue, and its Al, V and Ni removal ability, in 1,059.15 ± 197.28 mg kg^-1 of Al, 43.39 ± 24.13 mg kg^-1 of V and 0.58 ± 0.00 mg kg^-1 of Ni, corresponding to the 0.79%, 1.63% and 0.46% of each metal content, respectively, while no Ti removal was detected. Besides, it was observed that the sporulation process took place in B. megaterium cells in the presence of the spent catalyst. The results shown in this study suggest the potential of the strain MNSH1-9K-1 for the removal of metals contained in high-metal content residues, contributing also to the knowledge of the metal resistance and removal abilities of B. megaterium in the presence of a spent catalyst, and how morphological cell changes may be occurring while metal removal is taking place.

Evaluation of Mn bioaccumulation and biosorption by bacteria isolated from spent nuclear fuel pools using 54Mn as a radioindicator

Bioaccumulation and biosorption characteristics of Mn2+ions by both dead and living, non-growing biomass of Gram-positive bacteriaKocuria palustrisandMicrococcus luteusisolated from spent nuclear fuel pools were compared. The radioindicator method using radionuclide54Mn was applied to obtain precise and reliable data characterizing both processes as well as manganese distribution in bacterial cells. Manganese was mainly found on the surface (biosorption) of live cells of both bacteria and surface sorption capacity increased with Mn concentration in solution. Only 10.0% (M. luteus) and 6.3% (K. palustris) of uptaken Mn were localized in the cytoplasm (bioaccumulation). Biosorption of Mn by dead bacterial biomass was a rapid process strongly affected by solution pH. Maximum sorption capacitiesQmaxcalculated from the Langmuir isotherm and characterizing Mn binding represented 316±15 μmol/g forM. luteusand 282±16 μmol/g forK. palustris.Results indicate that living, non-growing cells showed a higher efficiency of Mn removal than dead biomass. Based on FTIR spectra examination with aim to characterize the surface ofK. palustrisandM. luteuscells, we confirmed that the phosphate and carboxyl functional groups are involved in manganese sorption onto cell surface by both live and dead bacterial biomass.

Exploited application of sulfate-reducing bacteria for concomitant treatment of metallic and non-metallic wastes: a mini review

A variety of multidimensional anthropogenic activities, especially of industrial level, are contaminating our aquatic and terrestrial environments with a variety of metallic and non-metallic pollutants. The metallic and non-metallic pollutants addressed specifically in this review are heavy metals and various compound forms of sulfates, respectively. Direct and indirect deleterious effects of the both types of pollutants to all forms of life are well-known. The treatment of such pollutants is therefore much necessary before their final discharge into the environment. This review summarizes the productive utility of sulfate-reducing bacteria (SRB) for economical and concomitant treatment of the above mentioned wastes. Utilization of agro-industrial wastes and some environmental contaminants including hydrocarbons, as economical growth substrates for SRB, is also suggested and proved efficient in this review. Mechanistically, SRB will utilize sulfates as their terminal electron acceptors during respiration while utilizing agro-industrial and/or hydrocarbon wastes as electron donors/carbon sources and generate H₂S. The biogenic H₂S will then react vigorously with dissolved metals present in the wastewaters thus forming metal sulfide. The metal sulfide being water insoluble and heavier than water will settle down in the water as precipitates. In this way, three types of pollutants i.e., metals, sulfates and agro-industrial and/or hydrocarbon wastes will be treated simultaneously.