Bacterial sorption of heavy metals

Bacterial nano-factories as a tool for the biosynthesis of TiO2 nanoparticles: characterization and potential application in wastewater treatment

The development of reliable and eco-conscious processes for nanoparticle synthesis constitutes a significant element in nanotechnology. TiO2 nanoparticles (NPs) are becoming essential due to their potential uses in dentistry, surgery, agriculture, and pharmacy. This leads to the development of various procedures for producing TiO2 NPs using various physicochemical methods. Still, the drawbacks of these conventional methods are associated with the emission of toxic chemicals into the atmosphere and high energy demands in production, hence endangering the health and the environment. Problems issued are solved by green nanotechnology, which offers tools as nano-factories by utilizing biological sources to subside the improper effects of conventional methods and produces nanoparticles through synthesis methods that are clean, safe, energy-efficient, and cost-effective. Among the biogenic sources, microbial cells such as bacteria possess intrinsic pathways of converting metallic salt to nanoparticles due to their ability to produce reductase enzymes. Also, they can offer features to products such as high dispersity and produce sustainable nanoparticles at a large scale. Biosynthesized TiO2 NPs have high oxidizing potential and a wide range of applications, specifically as photosensitizers and antimicrobial agents. This review will address bacterial nano-factories that can be utilized for the biosynthesis of TiO2 NPs, the characterization of biosynthesized nanoparticles, and their potential application in wastewater treatment.

A fluorescent sensor based on the cascade signal amplification strategy for ultra-sensitive detection of Cu2

Copper is an essential element in the human body, participating in various physiological activities in the bodies of organisms. However, an excessive load of Cu²⁺ is associated with several neurodegenerative diseases and prion diseases, also identified as a symptom of Wilson's disease (WD). A straightforward, rapid, sensitive, and specific copper sensor is highly required but remains a challenge. In this study, guided by the simulation, we developed a chemical sensor using a cascade signal amplification strategy based on the Cu-catalyzed click reaction, combined with a fluorescence-enhanced substrate with gold nanorods coupled with silver nanoislands. The sensor can selectively detect Cu²⁺ as low as 3.87 nM within 10 min. We have demonstrated that this method can be directly employed for WD diagnosis in urine samples. In addition, using antibiotic susceptibility testing (AST) as an example, we verify whether this assay can be adapted to other targets where Cu is designed as an indirect indicator.

Cadmium effects on net N2O production by the deep-sea isolate Shewanella loihica PV-4

Deep-sea mining may lead to the release of high concentrations of metals into the surrounding seabed, which can disturb important ecosystem functions provided by microbial communities. Among these, the production of N2O and its reduction to N2 is of great relevance since N2O is an important greenhouse gas. Metal impacts on net N2O production by deep-sea bacteria are, however, currently unexplored. Here, we evaluated the effects of cadmium (Cd) on net N2O production by a deep-sea isolate, Shewanella loihica PV-4. We performed a series of Cd exposure incubations in oxic conditions and determined N2O fluxes during induced anoxic conditions, as well as the relative expression of the nitrite reductase gene (nirK), preceding N2O production, and N2O reductase gene (nosZ), responsible for N2O reduction. Net N2O production by S. loihica PV-4 exposed to Cd was strongly inhibited when compared to the control treatment (no metal). Both nirK and nosZ gene expression were inhibited in reactors with Cd, but nirK inhibition was stronger, supporting the lower net N2O production observed with Cd. The Cd inhibition of net N2O production observed in this study poses the question whether other deep-sea bacteria would undergo the same effects. Future studies should address this question as well as its applicability to complex communities and other physicochemical conditions, which remain to be evaluated.

Bioavailability of Colloidal Iron to Heterotrophic Bacteria in Sediments, and Effects on the Mobility of Colloid-Associated Metal(loid)s

The submicrometric fraction of surface sediments that accumulate in the bottom of dam reservoirs represent important sources of nutrients and contaminants in freshwater systems. However, assessing their stability in the presence of sediment bacteria as well as their bioavailability in the sediment remains poorly understood. We hypothesized that sediment’s bacteria are able to extract nutrients from sedimentary colloids (<1 µm fraction) and thus contribute to the release of other colloid-associated elements to water. Experiments were performed under laboratory conditions, using the submicrometric fractions of sediments recovered from two dam reservoirs (in calcareous and crystalline granitic contexts) and two heterotrophic bacteria (Gram-negative Pseudomonas sp. and Gram-positive Mycolicibacterium sp.). The results demonstrated that bacteria were able to maintain their metabolic activity (the acidification of the growth medium and the production of organic ligands) in the presence of colloids as the sole source of iron (Fe) and regardless of their chemical composition. This demonstrates that bioavailable Fe, aside from ionic forms, can also occur in colloidal forms. However, the bacteria also catalyzed the release of potentially toxic metallic elements (such as Pb) associated with colloids. These results help improve our understanding of the processes that influence contaminants’ mobility in the ecosystems as well as provide an important insight into current research evaluating the bioavailability of different forms of nutrients.

Microorganisms Accelerate REE Mineralization in Supergene Environments

Exogenic deposits are an important source of rare earth elements (REEs), especially heavy REEs (HREEs). It is generally accepted that microorganisms are able to dissolve minerals and mobilize elements in supergene environments. However, little is known about the roles of microorganisms in the formation of exogenic deposits such as regolith-hosted REE deposits that are of HREE enrichment and provide over 90% of global HREE demand. In this study, we characterized the microbial community composition and diversity along a complete weathering profile drilled from a regolith-hosted REE deposit in Southeastern China and report the striking contributions of microorganisms to the enrichment of REEs and fractionation between HREEs and light REEs (LREEs). Our results provide evidence that the variations in REE contents are correlated with microbial community along the profile. Both fungi and bacteria contributed to the accumulation of REEs, whereas bacteria played a key role in the fractionation between HREEs and LREEs. Taking advantage of bacteria strains isolated from the profile, Gram-positive bacteria affiliated with Bacillus and Micrococcus preferentially adsorbed HREEs, and teichoic acids in the cell wall served as the main sites for HREE adsorption, leading to an enrichment of HREEs in the deposit. The present study provides the first database of microbial community in regolith-hosted REE deposits. These findings not only elucidate the crucial contribution of fungi and bacteria in the supergene REE mineralization but also provide insights into efficient utilization of mineral resources via a biological pathway.

IMPORTANCE Understanding the role of microorganisms in the formation of regolith-hosted rare earth element (REE) deposits is beneficial for improving the metallogenic theory and deposit exploitation, given that such deposits absolutely exist in subtropical regions with strong microbial activities. Little is known of the microbial community composition and its contribution to REE mineralization in this kind of deposit. Using a combination of high-throughput sequencing, batch adsorption experiments, and spectroscopic characterization, the functional microorganisms contributing to REE enrichment and fractionation are disclosed. For bacteria, the surface carboxyl and phosphate groups are active sites for REE adsorption, while teichoic acids in the cell walls of G⁺ bacteria lead to REE fractionation. The above-mentioned findings not only unravel the importance of microorganisms in the formation of supergene REE deposits but also provide experimental evidence for the bioutilization of REE resources.

Characterization of bio-adsorptive removal performance of strontium through ureolysis-mediated bio-mineralization

The adsorptive removal performance of strontium (Sr) through bio-mineralization metabolism under various parameters was evaluated in this study. The primary mechanism of bio-mineralization used in this study was the urea hydrolysis process through bacterial enzymatic catalysis. Bacillus sp, which was isolated from river sediment, was used as a ureolytic bacteria. Various environmental conditions were set as different initial concentrations of Sr (10, 50, 100, 200, and 500 mg/L), and various ratios of Mg/Ca (4, 2, 1, 0.5, and 0.25). The concentrations of Sr²⁺, Ca²⁺, and Mg²⁺ in the solution of the batch experiment were measured to identify the bio-mineralization performance and the removal rate of Sr. In addition, the main Sr removal mechanism of ureolytic bacteria was identified. As a result, for Sr removal of bacteria, the bio-mineralization mechanism was more predominant than the adsorption of Sr. The rapid growth and high nucleation site production were observed when the initial concentration of Sr²⁺ increased and the Mg/Ca ratio was lowered, resulting in high biomineralization performance and Sr removal rate. The main phases of carbonate minerals formed in the presence of Sr, Ca, and Mg were SrCO₃ and SrCa(CO₃)₂. Mg²⁺ could retard the bacterial growth and participate in the formation of carbonate minerals, when a large amount of Mg²⁺ was present. Furthermore, the desorption rate of Sr²⁺ from bacterial pastes containing the carbonate minerals increased as the concentration of HCl increased, although the carbonate minerals were in a stable state.

Effect of Endotoxemia Induced by Intraperitoneal Injection of Lipopolysaccharide on the Mg isotopic Composition of Biofluids and Tissues in Mice

Endotoxemia induced in vivo in mice by intraperitoneal injection of lipopolysaccharide (LPS) leads to (neuro)inflammation and sepsis. Also the homeostasis of mineral elements can be altered through mechanisms that still are poorly understood. The isotopic composition of Mg and the concentrations of the minor elements Ca, K, Mg, Na, P, and S were determined in biological fluids and tissues of young (14–28 weeks) and aged (40–65 weeks) LPS-injected mice and age-matched controls to reveal potential effects of the LPS-induced infection. Blood plasma of young and aged LPS-injected mice showed a heavy Mg isotopic composition, as well as elevated Mg and P concentrations, compared to matched controls. The plasma Mg isotopic composition was correlated with the P concentration in aged mice. Also the liver Mg isotopic composition was strongly affected in the young and aged LPS-injected mice, while for aged mice, an additional effect on the urine Mg isotopic composition was established. These observations were hypothetically associated with liver inflammation and/or hepatotoxicity, and reduced urinary Mg excretion, respectively. Also a regional endotoxin-induced difference was observed in the brain Mg isotopic composition for the aged mice only, and was attributed to potential disruption of the blood-brain barrier.

Extraction of valuable metals from discarded AMOLED displays in smartphones using Bacillus foraminis as an alkali-tolerant strain

With the alarming rate of e-waste generation, resource recovery from secondary metal sources is essential for sustainable resource utilization and to prevent the release of potentially toxic elements into the environment. In the current study, the first-time extraction of Ag, Mo, and Cu from active-matrix organic light-emitting diode (AMOLED) screens of discarded smartphones have been achieved using organic acids produced by Bacillus foraminis cultured on a modified Horikoshi medium. The influences of initial pH, inoculation size, and pulp density on the bioleaching process were evaluated over six-day experiment. Maximum extraction of Ag, Mo, and Cu (100, 56.8, and 41.4%) at optimal values of three investigated factors was obtained over a 12-day bioleaching experiment. A diverse assemblage of organic acid was produced in the optimized bioleaching condition, including tartaric (12.1 mM), formic (49.8 mM), acetic (21.5 mM), lactic (78.5 mM), citric (2.7 mM), and propionic (69.6 mM) acid. The contact angle analysis highlighted more hydrophobicity of powder after the bioleaching. FTIR and CHNO data also confirmed the role of bioleaching in the powder wettability alteration. The sequential extraction method revealed high mobility of In, Fe, Co, Cu, Cr, and Mo and low mobility of Ag. The results exhibited high tolerance of alkali-tolerant bacteria to potentially toxic elements and its superior performance in the bioleaching of discarded mobile screens at high pulp density.

Microbe-Mediated Biosynthesis of Nanoparticles: Applications and Future Prospects

Nanotechnology is the science of nano-sized particles/structures (~100 nm) having a high surface-to-volume ratio that can modulate the physical, chemical and biological properties of the chemical compositions. In last few decades, nanoscience has attracted the attention of the scientific community worldwide due to its potential uses in the pharmacy, medical diagnostics and disease treatment, energy, electronics, agriculture, chemical and space industries. The properties of nanoparticles (NPs) are size and shape dependent. These characteristic features of nanoparticles can be explored for various other applications such as computer transistors, chemical sensors, electrometers, memory schemes, reusable catalysts, biosensing, antimicrobial activity, nanocomposites, medical imaging, tumor detection and drug delivery. Therefore, synthesizing nanoparticles of desired size, structure, monodispersity and morphology is crucial for the aforementioned applications. Recent advancements in nanotechnology aim at the synthesis of nanoparticles/materials using reliable, innoxious and novel ecofriendly techniques. In contrast to the traditional methods, the biosynthesis of nanoparticles of a desired nature and structure using the microbial machinery is not only quicker and safer but more environmentally friendly. Various microbes, including bacteria, actinobacteria, fungi, yeast, microalgae and viruses, have recently been explored for the synthesis of metal, metal oxide and other important NPs through intracellular and extracellular processes. Some bacteria and microalgae possess specific potential to fabricate distinctive nanomaterials such as exopolysaccharides, nanocellulose, nanoplates and nanowires. Moreover, their ability to synthesize nanoparticles can be enhanced using genetic engineering approaches. Thus, the use of microorganisms for synthesis of nanoparticles is unique and has a promising future. The present review provides explicit information on different strategies for the synthesis of nanoparticles using microbial cells; their applications in bioremediation, agriculture, medicine and diagnostics; and their future prospects.

Nanomedicine: A Diagnostic and Therapeutic Approach to COVID-19

The SARS-CoV-2 virus is causing devastating morbidity and mortality worldwide. Nanomedicine approaches have a high potential to enhance conventional diagnostics, drugs and vaccines. In fact, lipid nanoparticle/mRNA vaccines are already widely used to protect from COVID-19. In this review, we present an overview of the taxonomy, structure, variants of concern, epidemiology, pathophysiology and detection methods of SARS-CoV-2. The efforts of repurposing, tailoring, and adapting pre-existing medications to battle COVID-19 and the state of vaccine developments are presented. Next, we discuss the broad concepts and limitations of how nanomedicine could address the COVID-19 threat. Nanomaterials are particles in the nanometer scale (10-100 nm) which possess unique properties related to their size, polarity, structural and chemical composition. Nanoparticles can be composed of precious metals (copper, silver, gold), inorganic materials (graphene, silicon), proteins, carbohydrates, lipids, RNA/DNA, or conjugates, combinations and polymers of all of the aforementioned. The advanced biochemical features of these nanoscale particles allow them to directly interact with virions and irreversibly disrupt their structure, which can render a virus incapable of replicating within the host. Virus-neutralizing coats and surfaces impregnated with nanomaterials can enhance personal protective equipment, hand sanitizers and air filter systems. Nanoparticles can enhance drug-based therapies by optimizing uptake, stability, target cell-specific delivery, and magnetic properties. In fact, recent studies have highlighted the potential of nanoparticles in different aspects of the fight against SARS-CoV-2, such as enhancing biosensors and diagnostic tests, drug therapies, designing new delivery mechanisms, and optimizing vaccines. This article summarizes the ongoing research on diagnostic strategies, treatments, and vaccines for COVID-19, while emphasizing the potential of nanoparticle-based pharmaceuticals and vaccines.

Chromium pollution and its bioremediation mechanisms in bacteria: A review

Environment pollution is at its peak and is creating havoc for living beings. Industrial wastes containing toxic pollutants have contributed to a great extent in this disastrous environment pollution. Chromium (Cr³⁺/Cr⁶⁺) is highly toxic and one of the most common environmental pollutants because of its extensive use in industries especially tanneries. Lack of efficient treatment methods has resulted in extensive chromium pollution. Bioremediation of chromium using bacteria is very thoughtful due to its eco-friendly and cost-effective outcome. Bacteria possess numerous mechanisms such as biosorption, reduction, efflux or bioaccumulation, naturally or acquired to counter the toxicity of chromium. This review focuses on the bacterial responses against chromium toxicity and scope for their application in bioremediation. The differences and similarities between Gram negative and positive bacteria against chromium are also highlighted. Further, the knowledge gap and future prospects are also discussed in order to fill these gaps and overcome the problem associated with real-time applicability of bacterial bioremediation.

Cadmium Immobilization in the Rhizosphere and Plant Cellular Detoxification: Role of Plant-Growth-Promoting Rhizobacteria as a Sustainable Solution

Food is the major cadmium (Cd)-exposure pathway from agricultural soils to humans and other living entities and must be reduced in an effective way. A plant can select beneficial microbes, like plant-growth-promoting rhizobacteria (PGPR), depending upon the nature of root exudates in the rhizosphere, for its own benefits, such as plant growth promotion as well as protection from metal toxicity. This review intends to seek out information on the rhizo-immobilization of Cd in polluted soils using the PGPR along with plant nutrient fertilizers. This review suggests that the rhizo-immobilization of Cd by a combination of PGPR and nanohybrid-based plant nutrient fertilizers would be a potential and sustainable technology for phytoavailable Cd immobilization in the rhizosphere and plant cellular detoxification, by keeping the plant nutrition flow and green dynamics of plant nutrition and boosting the plant growth and development under Cd stress.

Biosorption-based 64Cu-labeling of bacteria for pharmacokinetic positron-emission tomography

Biosorption-based bacterial ⁶⁴Cu-labeling and its application in pharmacokinetic positron-emission tomography (PET) were investigated. Both gram-positive and gram-negative bacteria were efficiently labeled with [⁶⁴Cu]Cu²⁺ ion in saline at room temperature within 5 min. The labeling ratio for Escherichia coli drastically decreased with trypsin pretreatment and the co-presence of excess Cu²⁺ ion, indicating the existence of specific Cu²⁺ binding sites on the E. coli cell surface. Washing with lysogeny broth medium was effective in purifying ⁶⁴Cu-labeled E. coli for kinetic study; the labeling stability was approximately 90% in serum for 15 min. According to dynamic PET imaging in colon-26 tumor-bearing mice, ⁶⁴Cu-labeled E. coli immediately disappeared from the blood circulation and primarily accumulated in the liver. In addition, transient pulmonary distribution was observed, being in a dose-dependently accelerated manner. Considering the simplicity and versatility of biosorption-based bacterial ⁶⁴Cu-labeling without genetic modification, the early-phase pharmacokinetic PET with ⁶⁴Cu-labeled bacteria is promising for assessing toxicological aspects of bacteria-mediated cancer therapy as well as a variety of bacterial pathogenicities in infectious diseases.

Biosorption of Rare Earth Elements by Different Microorganisms in Acidic Solutions

Acidic solutions from metal bioleaching processes usually contain mixtures of metals in different concentrations which need to be separated and concentrated in downstream processing. Aim of this study was to explore and compare biosorption of rare earth elements (REE) by different microorganisms in acidic solutions. Biosorption of REE by bacteria and fungi showed element selective biosorption. The gram-positive bacterium Bacillus subtilis showed a higher selectivity to ytterbium (Yb) and lutetium (Lu) than the gram-negative bacteria Leisingera methylohalidivorans and Phaeobacter inhibens. In contrast, the tested fungi (Catenulostroma chromoblastomyces, Pichia sp.) showed a preference for the middle rare earth elements. Algae exhibited a low biosorption performance. Additionally, for B. subtilis and one yeast (Pichia sp.), better results were achieved with living than dead biomass. This study compares for the first time biosorption of different microorganisms at standardized conditions at low pH und application related conditions.

Role of Microorganisms in the Remediation of Wastewater in Floating Treatment Wetlands: A Review

This article provides useful information for understanding the specific role of microbes in the pollutant removal process in floating treatment wetlands (FTWs). The current literature is collected and organized to provide an insight into the specific role of microbes toward plants and pollutants. Several aspects are discussed, such as important components of FTWs, common bacterial species, rhizospheric and endophytes bacteria, and their specific role in the pollutant removal process. The roots of plants release oxygen and exudates, which act as a substrate for microbial growth. The bacteria attach themselves to the roots and form biofilms to get nutrients from the plants. Along the plants, the microbial community also influences the performance of FTWs. The bacterial community contributes to the removal of nitrogen, phosphorus, toxic metals, hydrocarbon, and organic compounds. Plant–microbe interaction breaks down complex compounds into simple nutrients, mobilizes metal ions, and increases the uptake of pollutants by plants. The inoculation of the roots of plants with acclimatized microbes may improve the phytoremediation potential of FTWs. The bacteria also encourage plant growth and the bioavailability of toxic pollutants and can alleviate metal toxicity.

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.

Co-effect of minerals and Cd(II) promoted the formation of bacterial biofilm and consequently enhanced the sorption of Cd(II)

Heavy metal pollution is very common in soils. Soils are complex systems including minerals, bacteria, and various other substances. In Cd(II) contaminated soil, the combined effects of clay minerals and heavy metals on bacterial biofilm and Cd(II) adsorption are unappreciated. Our study showed that the combination of clay minerals (goethite, kaolinite, and montmorillonite) and heavy metals promoted Serratia marcescens S14 biofilm development significantly more than clay minerals or Cd(II) alone. The amount of biofilm after binary treatment with clay minerals and Cd(II) was 2.3-7.3 times than that in control. Mineral-induced cell death and the expression of the fimA, bsmA, and eps were key players in biofilm formation. Binary treatment with montmorillonite and Cd(II) significantly enhanced biofilm development and consequently increased the adsorption of Cd(II). Cd(II) removal is the result of co-adsorption of bacteria and minerals. Bacterial biofilm played an important role in Cd(II) adsorption. FTIR spectroscopy showed the components of biofilm were not affected by minerals and revealed the functional groups -OH, -NH, -CH₂, -SH, -COO participated in Cd(II) immobilization. Our findings are of fundamental significance for understanding how minerals and Cd(II) affect biofilms and thereby enhance Cd(II) adsorption and predicting the mobility and fate of heavy metals in heavy metal-contaminated soil.

Effect of Fe-metabolizing bacteria and humic substances on magnetite nanoparticle reactivity towards arsenic and chromium

Magnetite is a magnetic, Fe(II)-Fe(III)-mineral formed through abiogenic and biogenic pathways. It constitutes an attractive material for remediation due to its reactivity, large surface-area-to-volume ratio when present as nanoparticles, and magnetic recoverability. Magnetite can be repeatedly microbially oxidized or reduced, but it is unclear how this influences the reactivity of magnetite towards toxic metal or metalloid contaminants. In this study, magnetite (both abiogenic and biogenic) was exposed to microbial Fe(II) oxidation and Fe(III) reduction, before reacted with hexavalent chromium (Cr(VI)) or pentavalent arsenic (As(V)). Results showed microbial reduction of both magnetite types improved the removal rate of Cr(VI) from solution, though surprisingly microbial Fe(II)-oxidation also showed enhanced reactivity towards Cr(VI) compared to un-treated magnetite. Synchrotron based analysis confirmed the formation of Cr(III) at the surface of the magnetite. Reactivity with As was less dramatic and showed un-treated material was able to remove As(V) from solution faster than microbially Fe(III)-reduced and Fe(II)-oxidized magnetite. The presence of humic substances was also shown to lead to a decreased reactivity of biogenic and abiogenic magnetite towards As(V) and Cr(VI). Our results imply that Fe-metabolizing bacteria influence the immobilization of contaminants and should be considered when evaluating remediation schemes, especially where Fe-metabolizing bacteria are active.

The accumulation of rare-earth yttrium ions by Penicillium sp. ZD28

To obtained fungal resources with excellent tolerance and accumulation capacity to rare earth yttrium ions (Y³⁺), rare earth ore samples were collected and used for microbial screening. A fungus hyper-resistant to Y³⁺ was obtained and the effects of the fungus in three physiological states (growth process, mycelial pellets with physiological activity and the fungus powder after being ground) on the Y³⁺ accumulation were investigated. The Y³⁺ resistant fungus was identified as Penicillium sp. ZD28, and its mycelium pellets (about 1 mm in diameter) showed poor ability to accumulate Y³⁺ with an adsorption capacity of less than 81 μmol/g. However, the fungus was able to remove 99% of Y³⁺ during the growth process, at an initial concentration of less than 600 μM. Bioaccumulation of Y was observed on the cell surface of the ZD28 strain by elemental mapping using scanning electron microscopy-energy dispersive X-ray spectroscopy. The adsorbent (the dry fungal powder) had a remarkable adsorption property for Y³⁺ that was greater than 455 μmol/g in conditions of 465 μM < [Y³⁺] < 6382 μM. Penicillium sp. ZD28 has major potential applications in the accumulation of yttrium group rare earth ions. This research has formed a theoretical foundation for the application of this biological method to extract rare earth ions in the mining and smelting of yttrium group rare earth elements.

Multimetal bioremediation and biomining by a combination of new aquatic strains of Mucor hiemalis

Here we describe a unique microbial biotechnology for simultaneous bioremediation and biomining of twelve ionic metals overcoming the obstacles of multimetal toxicity to microbes. After a thorough search of key microorganisms in microbiomes of many sulfidic springs in Bavaria (Germany) over an area of 200 km², we found three new strains EH8, EH10 and EH11 of Mucor hiemalis physiologically compatible and capable of multimetal-remediation and enrichment. We combined the multimetal-resistance, hyper-accumulation and elicitation power of EH8, EH10 and EH11 to develop a novel biotechnology for simultaneous removal, fractionation and enrichment of metal ions. As a first step we showed the intracellular fixing and deposition of mercury as nanospheres in EH8's sporangiospores. Scanning Electron Microscopy-Energy-Dispersive X-Ray analysis revealed binding and precipitation of other applied metal ions as spherical nano-particles (~50-100 nm) at the outer electro-negative cellwall-surface of EH8, EH10 and EH11 sporangiospores. Microbiomes, germinated spores and dead insoluble cellwalls of these strains removed >81-99% of applied Al, Cd, Co, Cr, Cu, Hg, Ni, Pb, U, and Zn simultaneously and furthermore enriched precious Ag, Au and Ti from water all within 48 h, demonstrating the potential of new biotechnologies for safe-guarding our environment from metal pollution and concentrating precious diluted, ionic metals.

Immobilization of cadmium and lead by Lactobacillus rhamnosus GR-1 mitigates apical-to-basolateral heavy metal translocation in a Caco-2 model of the intestinal epithelium

Heavy metals are highly toxic elements that contaminate the global food supply and affect human and wildlife health. Purification technologies are often too expensive or not practically applicable for large-scale implementation, especially in impoverished nations where heavy metal contamination is widespread. Lactobacillus rhamnosus GR-1 (LGR-1) was shown in previous work to reduce heavy metal bioaccumulation in a Tanzanian cohort of women and children through indeterminant mechanisms. Here, it was hypothesized that LGR-1 could sequester the heavy metals lead (Pb) and cadmium (Cd), thereby reducing their absorption across intestinal epithelium. LGR-1 and other lactobacilli significantly reduced the amount of Pb and Cd in solution at all concentrations tested (0.5 mg/L - 50 mg/L) and exhibited sustained binding profiles over a 48-hour period. Relative binding efficiency of LGR-1 decreased as Pb concentration increased, with an absolute minimum binding threshold apparent at concentrations of 2 mg/L and above. Electron microscopy revealed that Pb formed irregular cell-surface clusters on LGR-1, while Cd appeared to form intracellular polymeric clusters. Additionally, LGR-1 was able to significantly reduce apical-to-basolateral translocation of Pb and Cd in a Caco-2 model of the intestinal epithelium. These findings demonstrate the absorbent properties of LGR-1 can immobilize Pb and Cd, effectively reducing their translocation across the intestinal epithelium in vitro. Oral administration of heavy metal-binding Lactobacillus spp. (many of which are known human symbionts and strains of established probiotics) may offer a simple and effective means to reduce the amount of heavy metals absorbed from foods in contaminated regions of the world.

Effects and Mechanisms of Microbial Remediation of Heavy Metals in Soil: A Critical Review

The use of microbes to change the concentration of heavy metals in soil and improve the ability of plants to deal with elevated metals concentrations has significant economic and ecological benefits. This paper reviews the origins and toxic effects of heavy metal pollution in soil, and describes the heavy metal accumulation mechanisms of microbes, and compares their different bioconcentration abilities. Biosorption, which depends on the special structure of the cell wall, is found to be the primary mechanism. Furthermore, Escherichia coli are found to adsorb more heavy metals than other species. Factors influencing microbial treatment of wastewater and soil containing heavy metals include temperature, pH, and different substrates. Finally, problems in the application of microbial treatment of heavy metal contamination are considered, and possible directions for future research are discussed.

CuO and ZnO Nanoparticles Modify Interkingdom Cell Signaling Processes Relevant to Crop Production

As the world population increases, strategies for sustainable agriculture are needed to fulfill the global need for plants for food and other commercial products. Nanoparticle formulations are likely to be part of the developing strategies. CuO and ZnO nanoparticles (NPs) offer potential as fertilizers, as they provide bioavailable essential metals, and as pesticides, because of dose-dependent toxicity. Effects of these metal oxide NPs on rhizosphere functions are the focus of this review. These NPs at doses of ≥10 mg metal/kg change the production of key metabolites involved in plant protection in a root-associated microbe, Pseudomonas chlororaphis O6. Altered synthesis occurs in the microbe for phenazines, which function in plant resistance to pathogens, the pyoverdine-like siderophore that enhances Fe bioavailability in the rhizosphere and indole-3-acetic acid affecting plant growth. In wheat seedlings, reprogramming of root morphology involves increases in root hair proliferation (CuO NPs) and lateral root formation (ZnO NPs). Systemic changes in wheat shoot gene expression point to altered regulation for metal stress resilience as well as the potential for enhanced survival under stress commonly encountered in the field. These responses to the NPs cross kingdoms involving the bacteria, fungi, and plants in the rhizosphere. Our challenge is to learn how to understand the value of these potential changes and successfully formulate the NPs for optimal activity in the rhizosphere of crop plants. These formulations may be integrated into developing practices to ensure the sustainability of crop production.

Characterizing the behavior, uptake, and toxicity of NM300K silver nanoparticles in Caenorhabditis elegans

Using Caenorhabditis elegans as a model organism, we addressed the potential linkage among toxicity of NM300K Ag nanoparticles (AgNPs), their particle size distribution, and the presence of dissolved Ag in the test media. Of the 3 endpoints assessed (growth, fertility, and reproduction), reproduction was the most sensitive, with the 50% effect concentration (EC50) ranging from 0.26 to 0.84 mg Ag L^-1 and 0.08 to 0.11 mg Ag L^-1 for NM300K and AgNO₃ , respectively. Silver uptake by C. elegans was similar for both forms of Ag, whereas bioaccumulation was higher in AgNO₃ exposure. The observed differences in toxicity between NM300K and AgNO₃ did not correlate with bioaccumulated Ag, which suggests that toxicity is a function of the type of exposing agent (AgNPs vs AgNO₃ ) and its mode of action. Before addition of the food source (Escherichia coli), size fractionation revealed that dissolved Ag comprised 13 to 90% and 4 to 8% of total Ag in the AgNO₃ and NM300K treatments, respectively. No dissolved Ag was detectable in the actual test media due to immediate Ag adsorption to bacteria. The results of the present study indicate that information on behavior and characterization of exposure conditions is essential for nanotoxicity studies. Environ Toxicol Chem 2018;37:1799-1810. © 2018 SETAC.

Enhanced Removal of Dissolved Hg(II), Cd(II), and Au(III) from Water by Bacillus subtilis Bacterial Biomass Containing an Elevated Concentration of Sulfhydryl Sites

In this study, the sorption of Hg(II), Cd(II), and Au(III) onto Bacillus subtilis biomass with an elevated concentration of sulfhydryl sites, induced by adding excess glucose to the growth medium (termed 'High Sulfhydryl Bacillus subtilis' or HSBS) was compared to that onto B. subtilis biomass with a low concentration of sulfhydryl sites (termed 'Low Sulfhydryl Bacillus subtilis' or LSBS) and to sorption onto a commercially available cation exchange resin. Our results show that HSBS exhibits sorption capacities for the three studied metals that are two to five times greater than the sorption capacities of LSBS for these metals. After blocking the bacterial cell envelope sulfhydryl sites using a qBBr treatment, the sorption of the metals onto HSBS was significantly inhibited, indicating that the enhanced sorption onto HSBS was mainly due to the elevated concentration of sulfhydryl sites on the bacteria. A direct comparison of the removal capacity of the HSBS and that of the cation exchange resin for the three metals demonstrates that HSBS, compared to this commercially available resin, exhibits superior sorption capacity and selectivity for the removal of Hg(II), Cd(II), and Au(III), especially in systems with dilute metal concentrations. These results suggest that bacterial sulfhydryl sites control the sorption behavior of these three metals, and therefore biomass with induced high concentrations of sulfhydryl sites represents a promising and low cost biosorbent for the effective removal and recovery of chalcophile heavy metals from aqueous media.

Staphylococcus carnosus: from starter culture to protein engineering platform

Since the 1950s, Staphylococcus carnosus is used as a starter culture for sausage fermentation where it contributes to food safety, flavor, and a controlled fermentation process. The long experience with S. carnosus has shown that it is a harmless and "food grade" species. This was confirmed by the genome sequence of S. carnosus TM300 that lacks genes involved in pathogenicity. Since the development of a cloning system in TM300, numerous genes have been cloned, expressed, and characterized and in particular, virulence genes that could be functionally validated in this non-pathogenic strain. A secretion system was developed for production and secretion of industrially important proteins and later modified to also enable display of heterologous proteins on the surface. The display system has been employed for various purposes, such as development of live bacterial delivery vehicles as well as microbial biocatalysts or bioadsorbents for potential environmental or biosensor applications. Recently, this surface display system has been utilized for display of peptide and protein libraries for profiling of protease substrates and for generation of various affinity proteins, e.g., Affibody molecules and scFv antibodies. In addition, by display of fragmented antigen-encoding genes, the surface expression system has been successfully used for epitope mapping of antibodies. Reviews on specific applications of S. carnosus have been published earlier, but here we provide a more extensive overview, covering a broad range of areas from food fermentation to sophisticated methods for protein-based drug discovery, which are all based on S. carnosus.

Cesium-induced inhibition of bacterial growth of Pseudomonas aeruginosa PAO1 and their possible potential applications for bioremediation of wastewater

Radioactive isotopes and fission products have attracted considerable attention because of their long lasting serious damage to the health of humans and other organisms. This study examined the toxicity and accumulation behavior of cesium towards P. aeruginosa PAO1 and its capacity to remove cesium from waste water. Interestingly, the programmed bacterial growth inhibition occurred according to the cesium environment. The influence of cesium was analyzed using several optical methods for quantitative evaluation. Cesium plays vital role in the growth of microorganisms and functions as an anti-microbial agent. The toxicity of Cs to P. aeruginosa PAO1 increases as the concentration of cesium is increased in concentration-dependent manner. P. aeruginosa PAO1 shows excellent Cs removal efficiency of 76.1% from the contaminated water. The toxicity of cesium on the cell wall and in the cytoplasm were studied by transmission electron microscopy and electron dispersive X-ray analysis. Finally, the removal of cesium from wastewater using P. aeruginosa PAO1 as a potential biosorbent and the blocking of competitive interactions of other monovalent cation, such as potassium, were assessed. Overall, P. aeruginosa PAO1 can be used as a high efficient biomaterial in the field of radioactive waste disposal and management.

Construction and evaluation of a modular biofilm-forming chamber for microbial recovery of neodymium and semi-continuous biofilm preparation. Tolerance of Serratia sp.N14 on acidic conditions and neutralized aqua regia

Recovery of neodymium from liquid metallic wastes and scrap leachates is a crucial step for its recycling, which can take place through the immobilized biofilms of Serratia sp. N14. These biofilms are produced in a fermentor vessel with a turnaround time of 10-14 days, which is unacceptable from an economic point of view for an industrial process. This study proposes the construction and evaluation of a modular system, whereby a biofilm-forming chamber is inserted into the continuous biomass outflow of the main chemostat vessel, for an alternative semi-continuous and economic production of biofilm. The activity of the biofilm from the outflow chamber was found to be the same as the one from the main chamber, which was stored in a cold room (4°C), for 9-12 months, depending on a 24 h nucleation step.Moreover, the ability of the biofilm to function in the presence of a leaching agent (aqua regia) or in acidic conditions was also evaluated. The biofilm of the main chamber can remain active even at 50% neutralized aqua regia (pH 3.0), while at acidic conditions, phosphate release of the cells is reduced to 50%. This strain proves to be very tolerant in low pH or high salt concentration solutions. The biofilm produced from the outflow of the main fermentor vessel is of acceptable activity, rather than being disposed.

Influence of bacterial extracellular polymeric substances on the sorption of Zn on γ-alumina: A combination of FTIR and EXAFS studies

Extracellular polymeric substances (EPS) isolated from bacteria, are abound of functional groups which can react with metals and consequently influence the immobilization of metals. In this study, we combined with Zn K-edge Extended X-ray Absorption Fine Structure (EXAFS), Fourier Transform Infrared (FTIR) spectroscopy, and High-Resolution Transmission Electron Microscopy (HRTEM) techniques to study the effects of EPS isolated from Bacillus subtilis and Pseudomonas putida on Zn sorption on γ-alumina. The results revealed that Zn sorption on aluminum oxide was pH-dependent and significantly influenced by bacterial EPS. At pH 7.5, Zn sorbed on γ-alumina was in the form of Zn-Al layered doubled hydroxide (LDH) precipitates, whereas at pH 5.5, Zn sorbed on γ-alumina was as a Zn-Al bidentate mononuclear surface complex. The amount of sorbed Zn at pH 7.5 was 1.3-3.7 times higher than that at pH 5.5. However, in the presence of 2 g L^-1 EPS, regardless of pH conditions and EPS source, Zn + EPS + γ-alumina ternary complex was formed on the surface of γ-alumina, which resulted in decreased Zn sorption (reduced by 8.4-67.8%) at pH 7.5 and enhanced Zn sorption (increased by 10.0-124.7%) at pH 5.5. The FTIR and EXAFS spectra demonstrated that both the carboxyl and phosphoryl moieties of EPS were crucial in this process. These findings highlight EPS effects on Zn interacts with γ-alumina.

Nanotechnology, Metal Nanoparticles, and Biomedical Applications of Nanotechnology

Nanotechnology has emerged as an important field of modern scientific research due to its diverse range of applications in the area of electronics, material sciences, biomedical engineering, and medicines at nano levels such as healthcare, cosmetics, food and feed, environmental health, optics, biomedical sciences, chemical industries, drug-gene delivery, energy science, optoelectronics, catalysis, reprography, single electron transistors, light emitters, nonlinear optical devices, and photoelectrochemical applications and other applications. Due to these immense applications of nanotechnology in biomedical science, it has became possible to design the pharmaceuticals in such a way that they could directly treat diseased cells like cancer and make microscopic repairs in hard-to-operate-on areas of the body. The nanomachines have been designed to clean up toxins or oil spills, recycle all garbage, eliminate landfills, etc. The chapter summarizes the present and future applications of nanotechnology for human welfare but needs further study in catalysis, optical devices, sensor technology, cancer treatment, and drug delivery systems.

Comparative mathematical modelling of a green approach for bioaccumulation of cobalt from wastewater

Cobalt is an essential element, but its wide use in industry generates important environmental and biological problems. The present study explores theoretical and empirical models of a green process for cobalt {Co²⁺} bioaccumulation from aqueous solutions. Two Gram-positive Bacillus subtilis species, strains CECT 4522 and LMM (the latter a former laboratory isolate from wastewater samples, which was phylogenetically characterized for the present work), were selected among others as the best Co²⁺ accumulation systems. Mathematical models representing kinetic and steady-state conditions for discrete and large amounts of bacterial biomass were expanded. In this way, it was possible to theoretically calculate the amount of Co²⁺ retained on the outer cell wall layer and incorporated inside the cell at any time. Theoretical and empirical hyperbolic-type models were suitable to fit the experimental bioaccumulation data for discrete amounts of bacteria biomass. In addition, kinetic relationships between the amount of Co²⁺ accumulated and the time before (or after) reaching steady state were established for large amounts of bacterial biomass. Other kinetic approaches were also satisfactorily tested. The two Gram-positive bacteria assayed are promising agents for developing heavy metal removal systems from industrial waste.

Remediation of sewage and industrial effluent using bacterially assisted floating treatment wetlands vegetated with Typha domingensis

This investigation reports the quantitative assessment of endophyte-assisted floating treatment wetlands (FTWs) for the remediation of sewage and industrial wastewater. Typha domingensis was used to vegetate FTWs that were subsequently inoculated with a consortium of pollutant-degrading and plant growth-promoting endophytic bacteria. T. domingensis, being an aquatic species, holds excellent potential to remediate polluted water. Nonetheless, investigation conducted on Madhuana drain carrying industrial and sewage water from Faisalabad City revealed the percentage reduction in chemical oxygen demand (COD) and biochemical oxygen demand (BOD₅) to be 87% and 87.5%, respectively, within 96 h on coupling the plant species with a consortium of bacterial endophytes. With the endophytes surviving in plant tissue, maximal reduction was obtained in not only the aforementioned pollution parameters but for other major environmental quality parameters including nutrients (N and P), ions (Na⁺ and K⁺), Cl^-, and SO₄^2- as well, which showed percentage reductions up to 90%, 39%, 77%, 91.8%, 40%, and 60%, respectively. This significant improvement in polluted wastewater quality treated with the proposed method render it safe to be discharged freely in larger water bodies as per the National Environmental Quality Standards (NEQS) of Pakistan or to be reused safely for irrigation purposes; thus, FTWs provide a sustainable and affordable approach for in situ remediation of sewage and industrial wastewater.

Attenuation of Microbial Stress Due to Nano-Ag and Nano-TiO2 Interactions under Dark Conditions

Engineered nanomaterials (ENMs) are incorporated into thousands of commercial products, and their release into environmental systems creates complex mixtures with unknown toxicological outcomes. To explore this scenario, we probe the chemical and toxicological interactions of nanosilver (n-Ag) and nanotitania (n-TiO₂) in Lake Michigan water, a natural aqueous medium, under dark conditions. We find that the presence of n-Ag induces a stress response in Escherichia coli, as indicated by a decrease in ATP production observed at low concentrations (in the μg L^-1 range), with levels that are environmentally relevant. However, when n-Ag and n-TiO₂ are present together in a mixture, n-TiO₂ attenuates the toxicity of n-Ag at and below 20 μg L^-1 by adsorbing Ag⁺_(aq). We observe, however, that toxic stress cannot be explained by dissolved silver concentrations alone and, therefore, must also depend on silver associated with the nanoscale fraction. Although the attenuating effect of n-TiO₂ on n-Ag's toxicity is limited, this study emphasizes the importance of probing the toxicity of ENM mixtures under environmental conditions to assess how chemical interactions between nanoparticles change the toxicological effects of single ENMs in unexpected ways.

Silver Nanoparticles: Synthesis, Characterization, Properties, Applications, and Therapeutic Approaches

Recent advances in nanoscience and nanotechnology radically changed the way we diagnose, treat, and prevent various diseases in all aspects of human life. Silver nanoparticles (AgNPs) are one of the most vital and fascinating nanomaterials among several metallic nanoparticles that are involved in biomedical applications. AgNPs play an important role in nanoscience and nanotechnology, particularly in nanomedicine. Although several noble metals have been used for various purposes, AgNPs have been focused on potential applications in cancer diagnosis and therapy. In this review, we discuss the synthesis of AgNPs using physical, chemical, and biological methods. We also discuss the properties of AgNPs and methods for their characterization. More importantly, we extensively discuss the multifunctional bio-applications of AgNPs; for example, as antibacterial, antifungal, antiviral, anti-inflammatory, anti-angiogenic, and anti-cancer agents, and the mechanism of the anti-cancer activity of AgNPs. In addition, we discuss therapeutic approaches and challenges for cancer therapy using AgNPs. Finally, we conclude by discussing the future perspective of AgNPs.

Assessment of agglomeration, co-sedimentation and trophic transfer of titanium dioxide nanoparticles in a laboratory-scale predator-prey model system

Nano titanium dioxide (nTiO₂) is the most abundantly released engineered nanomaterial (ENM) in aquatic environments. Therefore, it is prudent to assess its fate and its effects on lower trophic-level organisms in the aquatic food chain. A predator-and-prey-based laboratory microcosm was established using Paramecium caudatum and Escherichia coli to evaluate the effects of nTiO₂. The surface interaction of nTiO₂ with E. coli significantly increased after the addition of Paramecium into the microcosm. This interaction favoured the hetero-agglomeration and co-sedimentation of nTiO₂. The extent of nTiO₂ agglomeration under experimental conditions was as follows: combined E. coli and Paramecium > Paramecium only > E. coli only > without E. coli or Paramecium. An increase in nTiO₂ internalisation in Paramecium cells was also observed in the presence or absence of E. coli cells. These interactions and nTiO₂ internalisation in Paramecium cells induced statistically significant (p < 0.05) effects on growth and the bacterial ingestion rate at 24 h. These findings provide new insights into the fate of nTiO₂ in the presence of bacterial-ciliate interactions in the aquatic environment.

Cadmium sulphide quantum dots with tunable electronic properties by bacterial precipitation

We present a new method to fabricate semiconducting, transition metal nanoparticles (NPs) with tunable bandgap energies using engineered Escherichia coli. These bacteria overexpress the Treponema denticola cysteine desulfhydrase gene to facilitate precipitation of cadmium sulphide (CdS) NPs. Analysis with transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy reveal that the bacterially precipitated NPs are agglomerates of mostly quantum dots, with diameters that can range from 3 to 15 nm, embedded in a carbon-rich matrix. Additionally, conditions for bacterial CdS precipitation can be tuned to produce NPs with bandgap energies that range from quantum-confined to bulk CdS. Furthermore, inducing precipitation at different stages of bacterial growth allows for control over whether the precipitation occurs intra- or extracellularly. This control can be critically important in utilizing bacterial precipitation for the environmentally-friendly fabrication of functional, electronic and catalytic materials. Notably, the measured photoelectrochemical current generated by these NPs is comparable to values reported in the literature and higher than that of synthesized chemical bath deposited CdS NPs. This suggests that bacterially precipitated CdS NPs have potential for applications ranging from photovoltaics to photocatalysis in hydrogen evolution.

Uptake of radioiodide by Paenibacillus sp., Pseudomonas sp., Burkholderia sp. and Rhodococcus sp. isolated from a boreal nutrient-poor bog

Radionuclides, like radioiodine ((129)I), may escape deep geological nuclear waste repositories and migrate to the surface ecosystems. In surface ecosystems, microorganisms can affect their movement. Iodide uptake of six bacterial strains belonging to the genera Paenibacillus, Pseudomonas, Burkholderia and Rhodococcus isolated from an acidic boreal nutrient-poor bog was tested. The tests were run in four different growth media at three temperatures. All bacterial strains removed iodide from the solution with the highest efficiency shown by one of the Paenibacillus strains with >99% of iodide removed from the solution in one of the used growth media. Pseudomonas, Rhodococcus and one of the two Paenibacillus strains showed highest iodide uptake in 1% yeast extract with maximum values for the distribution coefficient (Kd) ranging from 90 to 270L/kg DW. The Burkholderia strain showed highest uptake in 1% Tryptone (maximum Kd 170L/kg DW). The Paenibacillus strain V0-1-LW showed exceptionally high uptake in 0.5% peptone +0.25% yeast extract broth (maximum Kd>1,000,000L/kg DW). Addition of 0.1% glucose to the 0.5% peptone +0.25% yeast extract broth reduced iodide uptake at 4°C and 20°C and enhanced iodide uptake at 37°C compared to the uptake without glucose. This indicates that the uptake of glucose and iodide may be competing processes in these bacteria. We estimated that in in situ conditions of the bog, the bacterial uptake of iodide accounts for approximately 0.1%-0.3% of the total sorption of iodide in the surface, subsurface peat, gyttja and clay layers.

Chemical speciation and bioavailability of cadmium in the temperate and semiarid soils treated with wheat residue

Heavy metal bioavailability depends on metal fractions in soil. The impacts of mild wheat residue (<2 mm) and incubation time on fractions of Cd were studied in two different spiked soils sampled from Hamadan and Lahijan, Iran with semiarid and temperate climates, respectively. Two factorial experiments were done in two soils polluted with 10 μg Cd g(-1) soil separately. Organic matter (0 and 5 % wheat straw) and soil incubation time (24 and 3600 h) were factors examined in three replicates. The transformation of Cd from KNO3 extractable form to less available fractions was higher in semiarid soils with lower clay and OM contents and higher pH and carbonate contents compared to temperate soils. In polluted semiarid soils after 24 h incubation, greater content of Cd was observed in residual (HNO3 extractable) (45 %), carbonates associated (EDTA extractable) (34 %), organic matter associated (NaOH extractable) (11 %), and KNO3 extractable (10 %) fractions, but in temperate soils, greater content of Cd was observed in KNO3 extractable (61 %), HNO3 extractable (14 %), EDTA extractable (13 %), and NaOH extractable (12 %) fractions. KNO3 extractable form of Cd was decreased, and NaOH extractable and HNO3 extractable forms of Cd were increased by addition of wheat residue to both soils. The initial decrease of added Cd from KNO3 extractable form to less mobile fractions in Hamadan soil was very interesting. But this change was not observed in Lahijan soil. Since contamination factor was significantly high in temperate soils compared to semiarid soils in all treatments, the risk of Cd environmental pollution in temperate region is considerably high.

Response surface methodology for cadmium biosorption on Pseudomonas aeruginosa

In this research the effects of various physicochemical factors on Cd(2+) biosorption such as initial metal concentration, pH and contact exposure time were studied. This study has shown a Cd(2+) biosorption, equilibrium time of about 5 min for Pseudomonas aeruginosa and the adsorption equilibrium data were well described by Langmuir equation. The maximum capacity for biosorption has been extrapolated to 0.56 mmol.g(-1) for P. aeruginosa. The thermodynamic properties ΔG(0), ΔH(0), and ΔS(0) of Cd(2+) for biosorption were analyzed by the equilibrium constant value obtained from experimented data at different temperatures. The results show that biosorption of Cd(2+) by P. aeruginosa are endothermic and spontaneous with ΔH value of 36.35 J.mol(-1). By response surface methodology, the quadratic model has adequately described the experimental data based on the adjusted determination coefficient (R(2) = 0.98). The optimum conditions for maximum uptake onto the biosorbent were established at 0.5 g.l(-1) biosorbent concentration, pH 6 for the aqueous solution, and a temperature of 30 °C.

Effect of UV-photofunctionalization on oral bacterial attachment and biofilm formation to titanium implant material

Bacterial biofilm infections remain prevalent reasons for implant failure. Dental implant placement occurs in the oral environment, which harbors a plethora of biofilm-forming bacteria. Due to its trans-mucosal placement, part of the implant structure is exposed to oral cavity and there is no effective measure to prevent bacterial attachment to implant materials. Here, we demonstrated that UV treatment of titanium immediately prior to use (photofunctionalization) affects the ability of human polymicrobial oral biofilm communities to colonize in the presence of salivary and blood components. UV-treatment of machined titanium transformed the surface from hydrophobic to superhydrophilic. UV-treated surfaces exhibited a significant reduction in bacterial attachment as well as subsequent biofilm formation compared to untreated ones, even though overall bacterial viability was not affected. The function of reducing bacterial colonization was maintained on UV-treated titanium that had been stored in a liquid environment before use. Denaturing gradient gel-electrophoresis (DGGE) and DNA sequencing analyses revealed that while bacterial community profiles appeared different between UV-treated and untreated titanium in the initial attachment phase, this difference vanished as biofilm formation progressed. Our findings confirm that UV-photofunctionalization of titanium has a strong potential to improve outcome of implant placement by creating and maintaining antimicrobial surfaces.