Chemical and enzymatic extraction of heavy metal binding polymers from isolated cell walls ofSaccharomyces cerevisiae

Copper Ion Mediates Yeast-to-Hypha Transition in Yarrowia lipolytica

Copper is an essential element that maintains yeast physiological function at low concentrations, but is toxic in excess. This study reported that Cu(II) significantly promoted the yeast-to-hypha transition of Yarrowia lipolytica in dose-dependent manner. Strikingly, the intracellular Cu(II) accumulation was drastically reduced upon hyphae formation. Moreover, we investigated the effect of Cu(II) on the physiological function of Y. lipolytica during the dimorphic transition and found that cellular viability and thermomyces lanuginosus lipase (TLL) were both influenced by the Cu(II)-induced yeast-to-hypha transition. Overall, hyphal cells survived better than yeast-form cells with copper ions. Furthermore, transcriptional analysis of the Cu(II)-induced Y. lipolytica before and after hyphae formation revealed a transition state between them. The results showed multiple differentially expressed genes (DEGs) were turned over between the yeast-to-transition and the transition-to-hyphae processes. Furthermore, gene set enrichment analysis (GSEA) identified that multiple KEGG pathways, including signaling, ion transport, carbon and lipid metabolism, ribosomal, and other biological processes, were highly involved in the dimorphic transition. Importantly, overexpression screening of more than thirty DEGs further found four novel genes, which are encoded by YALI1_B07500g, YALI1_C12900g, YALI1_E04033g, and YALI1_F29317g, were essential regulators in Cu-induced dimorphic transition. Overexpression of each of them will turn on the yeast-to-hypha transition without Cu(II) induction. Taken together, these results provide new insight to explore further the regulatory mechanism of dimorphic transition in Y. lipolytica.

Determination of elemental distribution and evaluation of elemental concentration in single Saccharomyces cerevisiae cells using single cell-inductively coupled plasma mass spectrometry

Single-cell analysis using inductively coupled plasma mass spectrometry (SC-ICP-MS) is a method to obtain qualitative and quantitative information of the elemental content and distribution of single cells. Six intrinsic target elements were analyzed in yeast cells at different cell growth phases cultured in medium with different phosphorus concentrations (0, 7, 14 mM) to study its effect on cell growth and composition. SC-ICP-MS results were compared with those obtained by the acid digestion and the average ratio was 0.81. The limits of detection of this method were 0.08, 2.54, 12.5, 0.02, 0.02, and 0.08 fg cell-1 for Mg, P, K, Mn, Cu, and Zn, respectively. During the exponential growth phase, the cells exhibited higher elemental contents, wider distribution for most elements, and larger cell size in comparison to the stationary growth phase. Phosphorus-free conditions reduced the average P content in single cells of stationary growth phase from 650 to 80 fg. Phosphorus deficiency led to decreasing intracellular concentrations not only of P but also of K and Cu, and to increasing Zn concentration after 48 h. Mg maintained its concentration at ∼0.11 fg µm-3 and did not change significantly under the three investigated conditions after 48 h. Accordingly, Mg content was successfully used to estimate the intracellular concentration of other intrinsic elements in single yeast cells. SC-ICP-MS is suited to determine target elements in single yeast cells, and allows the study of heterogeneity of cell composition and effects of stressors on the elemental content, distribution, and concentrations of intrinsic elements.

Adsorption process and mechanism of heavy metal ions by different components of cells, using yeast (Pichia pastoris) and Cu2+ as biosorption models

Microbial biomass has been recognized as an essential biosorbent to remove heavy metal ions, but the biosorption process and mechanism of different components of microbial cells have not been elucidated. In present study, Pichia pastoris X33 and Cu²⁺ was used as a biosorption model to reveal the biosorption process and mechanism of different components of microbial cells. For the biosorption of whole cells, the maximum removal efficiency was 41.1%, and the adsorption capacity was 6.2 mg g⁻¹. TEM-EDX analysis proved the existence of Cu²⁺ on the cell surface and cytoplasm. The maximum Cu²⁺ removal efficiency of the cell wall, cell membrane and cytoplasm were 21.2%, 20.7% and 18.5%, respectively. The optimum pH of Cu²⁺ biosorption of the P. pastoris cell, cell wall, cell membrane and cytoplasm was 6. Moreover, the maximum adsorption capacity of the cell, cell wall, cell membrane and cytoplasm was 16.13, 11.53, 10.97 and 8.87 mg g⁻¹, respectively. The maximum removal efficiencies of P. pastoris biomass treated with proteinase K and P. pastoris biomass treated with β-mannanase were 18.1% and 28.2%, respectively. The maximum removal efficiencies of mannan and glucan were 34% and 12%, respectively. The FTIR spectra showed that the amino group (N–H), hydroxyl (O–H), carbon oxygen bond (C–O), –CH, C–N and carbonyl group (C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O) of a ketone or aldehyde may interact with Cu²⁺. Thus, our work provides guidance for further understanding the effect of different cell components on biosorption.

The Cu²⁺ first bound to the outer mannan and finally entered the cytoplasm. During the whole adsorption process, the number of adsorption sites in the outer and middle cell walls was the largest, and then gradually decreased.

Terbium Excitation Spectroscopy as a Detection Method for Chromatographic Separation of Lanthanide-Binding Biomolecules

Studies of biosorption and bioaccumulation of heavy metals deal mostly with challenging, inhomogeneous, and complex materials. Therefore, most reports describe only application studies, while fundamental research is limited to indirect methods and speculations on the binding mechanisms. In this study, we describe a method for detecting and isolating heavy metal-binding biomolecules directly from crude extracts. The underlying principle is terbium sensitization and fluorescence excitation spectroscopy used offline after a chromatographic run. Compounds interacting with metal ions inevitably change the coordination sphere of terbium, which is reflected in the excitation spectrum leading to metal-specific luminescence. Main advantages of our approach include simple, fast, and inexpensive experiment design, nondestructive measurements, and detection limits far below 1 mg. Here, we have applied our method for three promising biosorbents (green algae, moss, and cyanobacterium) and obtained first information on the character of active compounds isolated from each species.

Cadmium binding characterization and mechanism of a newly isolated strain Cystobasidium oligophagum QN-3

The aim of this study was to screen a strain for the removal of Cd²⁺ from aqueous solution and investigate the characterization and mechanism of the Cd²⁺ binding process. A novel strain of yeast showed high tolerance of cadmium, namely Cystobasidium oligophagum QN-3, was isolated from soils, which could resist 22,000 mg/L and 18,000 mg/L Cd²⁺ on PDA (potato dextrose agar) plate and in PDA liquid medium, respectively. Cd²⁺ binding experiment showed that the strain could remove Cd²⁺ from aqueous solution effectively, the maximum Cd²⁺ removal rate of 84.45% was achieved at initial Cd²⁺ concentration 30 mg/L. Scanning electron microscopy (SEM) analysis revealed that sorption of Cd²⁺ by cells could be associated with changes in the cell surface morphology. Fourier transform-infrared spectroscopy (FTIR) analysis confirmed the important role of the functional groups OH, CO, NH₂ , COO, PO, and CH on the cell surface in the binding of Cd²⁺ . The comparison of the binding ability of different cellular parts indicated a significant role of the cell wall played in the Cd²⁺ binding process. Pretreatment of the cells by boiling or ultrasonication could improve the biosorption capacity of QN-3. In addition, QN-3 exhibited selective and preferential property of binding capacity for other heavy metals, such as Pb²⁺ , Cu²⁺ , Cd²⁺ , Zn²⁺ , and Ni²⁺ . These data suggested the promising use of Cystobasidium oligophagum QN-3 as an effective and friendly biosorbent for cadmium or other heavy metals decontamination in the environment.

A lytic polysaccharide monooxygenase-like protein functions in fungal copper import and meningitis

Infection by the fungal pathogen Cryptococcus neoformans causes lethal meningitis, primarily in immune-compromised individuals. Colonization of the brain by C. neoformans is dependent on copper (Cu) acquisition from the host, which drives critical virulence mechanisms. While C. neoformans Cu+ import and virulence are dependent on the Ctr1 and Ctr4 proteins, little is known concerning extracellular Cu ligands that participate in this process. We identified a C. neoformans gene, BIM1, that is strongly induced during Cu limitation and which encodes a protein related to lytic polysaccharide monooxygenases (LPMOs). Surprisingly, bim1 mutants are Cu deficient, and Bim1 function in Cu accumulation depends on Cu2+ coordination and cell-surface association via a glycophosphatidyl inositol anchor. Bim1 participates in Cu uptake in concert with Ctr1 and expression of this pathway drives brain colonization in mouse infection models. These studies demonstrate a role for LPMO-like proteins as a critical factor for Cu acquisition in fungal meningitis.

Full-color emissive carbon-dots targeting cell walls of onion for in situ imaging of heavy metal pollution

Full-colour emissive carbon-dots were prepared and applied in targeting onion CWs for in situ imaging of heavy metal pollution.

Immobilized microbial biosorbents for heavy metals removal

Intensive industrial and urban growth has led to the release of increasing amounts of environmental pollutants. Contamination by metals, in particular, deserves special attention due to their toxicity and potential to bioaccumulate via the food chain. Conventional techniques for the removal of toxic metals, radionuclides and precious metals from wastewater all have a number of drawbacks, such as incomplete metal extraction, high cost and risk of generating hazardous by-products. Biosorption is a cost-effective and environment-friendly technology, an alternative to conventional wastewater treatment methods. Biosorption is a metabolically independent process, in which dead microbial biomass is capable of removal and concentrating metal ions from aqueous solutions. Free microbial biosorbents are of small size and low density, insufficient mechanical stability and low elasticity, which causes problems with metal ion desorption, separation of the sorbent from the medium and its regeneration. Hence, the possibilities for the implementation of continuous biosorbent processes for metal removal in flow-type reactor systems are reduced and the practical application of biosorption in industrial conditions is limited. By immobilizing microbial biomass on suitable carriers the disadvantages of free biosorbents are eliminated and more opportunities for practical use of biosorption become available. This review examines different immobilization techniques and carriers, certain basic features and possibilities of using immobilized microbial biosorbents for the removal and concentration of metals from aqueous solutions.

Effects of synbiotic supplementation on growth performance, carcass characteristics, meat quality and muscular antioxidant capacity and mineral contents in broilers

BACKGROUND

The present study aimed to investigate the effects of dietary synbiotic supplementation on growth performance, carcass composition, meat quality and muscular antioxidant capacity, and mineral contents in broilers. Accordingly, 96 day-old male broiler chicks (Arbor Acres Plus; Aviagen, Huntsville, AL, USA) were randomly allocated to two groups, and each group consisted of six replicates with eight chicks each. Birds were fed a corn-soybean meal basal diet supplemented with either 0 or 1.5 g kg^-1 synbiotic, consisting of probiotics (Bacillus subtilis, Bacillus licheniformis and Clostridium butyricum) and prebiotics (yeast cell wall and xylooligosaccharide) from 1 to 42 days of age.

RESULTS

Compared with the control group, supplementation with a synbiotic increased average daily gain (P < 0.05) but reduced feed/gain ratio (P < 0.01) in broilers from 1 to 42 days of age. Similalrly, dietary synbiotic inclusion increased breast yield (P < 0.05) but decreased abdominal fat (P < 0.01) in broilers. The breast muscle pH value at 24 h postmortem in broilers was elevated with the incorporation of synbiotic (P < 0.05). By contrast, synbiotic supplementation lowered the cooking loss during heat treatment in a water bath, malondialdehyde content, and total Cr content in the thigh muscle in broilers (P < 0.05).

CONCLUSION

Dietary synbiotic supplementation into the diet of broilers may be an effective method for improving growth performance and carcass compositions, resulting in the production of meat with a favorable quality and oxidative stability. © 2017 Society of Chemical Industry.

Ability of Soil Isolated Actinobacterial Strains to Prevent, Bind and Biodegrade Ochratoxin A

Ochratoxin A (OTA) is one of the most important mycotoxins, and contaminates several agricultural products, particularly cereals, grapes, maize, barley, spices and coffee. The aim of this project was to reduce the levels of OTA by supplementing the artificially contaminated solutions with seven strains of actinobacteria (AT10, AT8, SN7, MS1, ML5, G10 and PT1) in order to evaluate their capacity for binding and metabolizing the OTA, as well as their ability to reduce the expression of the genes responsible for its production in A. carbonarius. In the first part of this study, we evaluated the capacity of Streptomyces strains for binding OTA on their surfaces after 0, 30 and 60 min of incubation with PBS solution supplemented with OTA. In the second part, we tested the ability of these strains, as well as their supernatants, to detoxify the ISP2 medium. Finally, we studied the effect of the Streptomyces cocultured with Aspergillus carbonarius on the expression of OTA biosynthesis genes. Results showed that, among the strains co-cultured with A. carbonarius, the strain G10 was able to reduce the expression of acpks, acOTApks, acOTAnrps and vea genes, thus reducing OTA from solid PDA medium to 13.50% of reduction. This strain was remarkably able to detoxify and bind OTA up to 47.07%. Strain AT8 was stronger in detoxifying OTA (52.61%), but had no significant effect on the studied gene expression.

Heavy metal accumulation by Saccharomyces cerevisiae cells armed with metal binding hexapeptides targeted to the inner face of the plasma membrane

Accumulation of heavy metals without developing toxicity symptoms is a phenotype restricted to a small group of plants called hyperaccumulators, whose metal-related characteristics suggested the high potential in biotechnologies such as bioremediation and bioextraction. In an attempt to extrapolate the heavy metal hyperaccumulating phenotype to yeast, we obtained Saccharomyces cerevisiae cells armed with non-natural metal-binding hexapeptides targeted to the inner face of the plasma membrane, expected to sequester the metal ions once they penetrated the cell. We describe the construction of S. cerevisiae strains overexpressing metal-binding hexapeptides (MeBHxP) fused to the carboxy-terminus of a myristoylated green fluorescent protein (myrGFP). Three non-toxic myrGFP-MeBHxP (myrGFP-H6, myrGFP-C6, and myrGFP-(DE)3) were investigated against an array of heavy metals in terms of their effect on S. cerevisiae growth, heavy metal (hyper) accumulation, and capacity to remove heavy metal from contaminated environments.

Cell Surface Interference with Plasma Membrane and Transport Processes in Yeasts

The wall of the yeast Saccharomyces cerevisiae is a shell of about 120 nm thick, made of two distinct layers, which surrounds the cell. The outer layer is constituted of highly glycosylated proteins and the inner layer is composed of β-glucan and chitin. These two layers are interconnected through covalent linkages leading to a supramolecular architecture that is characterized by physical and chemical properties including rigidity, porosity and biosorption. The later property results from the presence of highly negative charged phosphate and carboxylic groups of the cell wall proteins, allowing the cell wall to act as an efficient barrier to metals ions, toxins and organic compounds. An intimate connection between cell wall and plasma membrane is indicated by the fact that changes in membrane fluidity results in change in cell wall nanomechanical properties. Finally, cell wall contributes to transport processes through the use of dedicated cell wall mannoproteins, as it is the case for Fit proteins implicated in the siderophore-iron bound transport and the Tir/Dan proteins family in the uptake of sterols.

Effects of different forms of yeast Saccharomyces cerevisiae on growth performance, intestinal development, and systemic immunity in early-weaned piglets

The present study was conducted to determine effects of different forms of yeast (Saccharomyces cerevisiae, strain Y200007) on the growth performance, intestinal development, and systemic immunity in early-weaned piglets. A total of 96 piglets (14-d old, initial average body weight of 4.5 kg) were assigned to 4 dietary treatments: (1) basal diet without yeast (Control); (2) basal diet supplemented with 3.00 g/kg live yeast (LY); (3) basal diet supplemented with 2.66 g/kg heat-killed whole yeast (HKY); and (4) basal diet supplemented with 3.00 g/kg superfine yeast powders (SFY). Diets and water were provided ad libitum to the piglets during 3-week experiment. Growth performance of piglets was measured weekly. Samples of blood and small intestine were collected at days 7 and 21 of experiment. Dietary supplementation with LY and SFY improved G:F of piglets at days 1-21 of the experiment (P < 0.05) compared to Control group. Serum concentrations of growth hormone (GH), triiodothyronine (T3), tetraiodothyronine (T4), and insulin growth factor 1 (IGF-1) in piglets at day 21 of the experiment were higher when fed diets supplemented with LY and SFY than those in Control group (P < 0.05). Compared to Control group, contents of serum urea nitrogen of piglets were reduced by the 3 yeast-supplemented diets (P < 0.05). Diets supplemented with LY increased villus height and villus-to-crypt ratio in duodenum and jejunum of piglets (P < 0.05) compared to other two groups at day 7 of the experiment. Feeding diets supplemented with LY and SFY increased (P < 0.05) serum concentrations of IgA, IL-2, and IL-6 levels in piglets compared to Control. The CD4(+)/CD8(+) ratio and proliferation of T-lymphocytes in piglets fed diets supplemented with LY were increased compared to that of Control group at day 7 of the experiment (P < 0.05). In conclusion, dietary supplementation with both LY and SFY enhanced feed conversion, small intestinal development, and systemic immunity in early-weaned piglets, with better improvement in feed conversion by dietary supplementation with LY, while dietary supplementation with SFY was more effective in increasing systemic immune functions in early-weaned piglets.

Copper Tolerance and Biosorption of Saccharomyces cerevisiae during Alcoholic Fermentation

At high levels, copper in grape mash can inhibit yeast activity and cause stuck fermentations. Wine yeast has limited tolerance of copper and can reduce copper levels in wine during fermentation. This study aimed to understand copper tolerance of wine yeast and establish the mechanism by which yeast decreases copper in the must during fermentation. Three strains of Saccharomyces cerevisiae (lab selected strain BH8 and industrial strains AWRI R2 and Freddo) and a simple model fermentation system containing 0 to 1.50 mM Cu2+ were used. ICP-AES determined Cu ion concentration in the must decreasing differently by strains and initial copper levels during fermentation. Fermentation performance was heavily inhibited under copper stress, paralleled a decrease in viable cell numbers. Strain BH8 showed higher copper-tolerance than strain AWRI R2 and higher adsorption than Freddo. Yeast cell surface depression and intracellular structure deformation after copper treatment were observed by scanning electron microscopy and transmission electron microscopy; electronic differential system detected higher surface Cu and no intracellular Cu on 1.50 mM copper treated yeast cells. It is most probably that surface adsorption dominated the biosorption process of Cu2+ for strain BH8, with saturation being accomplished in 24 h. This study demonstrated that Saccharomyces cerevisiae strain BH8 has good tolerance and adsorption of Cu, and reduces Cu2+ concentrations during fermentation in simple model system mainly through surface adsorption. The results indicate that the strain selected from China's stress-tolerant wine grape is copper tolerant and can reduce copper in must when fermenting in a copper rich simple model system, and provided information for studies on mechanisms of heavy metal stress.

Effect of the bread-making process on zearalenone levels

The effects of the bread-making process including fermentation with Saccharomyces cerevisiae and lactic acid bacteria (Lactobacillus casei, Lactobacillus rhamnosus, Lactobacillus acidophilus and Lactobacillus fermentum) and baking at 200°C on zearalenone (ZEA) levels were investigated. Standard solutions of ZEA were added to flour and then loaves of bread were prepared. Sourdough and three types of yeast including active dry yeast, instant dry yeast and compressed yeast were used for the fermentation of dough. ZEA levels in flour, dough and bread were determined by HPLC with fluorescence detection after extraction and clean-up on an immunoaffinity column. The highest reduction in levels of ZEA was found in the first fermentation (first proof), while the lowest reduction was observed in the baking stage. In addition, the results showed that compressed yeast had the maximum reduction potential on ZEA levels even at the baking stage.

Applied usage of yeast spores as chitosan beads

In this study, we present a nonhazardous biological method of producing chitosan beads using the budding yeast Saccharomyces cerevisiae. Yeast cells cultured under conditions of nutritional starvation cease vegetative growth and instead form spores. The spore wall has a multilaminar structure with the chitosan layer as the second outermost layer. Thus, removal of the outermost dityrosine layer by disruption of the DIT1 gene, which is required for dityrosine synthesis, leads to exposure of the chitosan layer at the spore surface. In this way, spores can be made to resemble chitosan beads. Chitosan has adsorptive features and can be used to remove heavy metals and negatively charged molecules from solution. Consistent with this practical application, we find that spores are capable of adsorbing heavy metals such as Cu(2+), Cr(3+), and Cd(2+), and removal of the dityrosine layer further improves the adsorption. Removal of the chitosan layer decreases the adsorption, indicating that chitosan works as an adsorbent in the spores. Besides heavy metals, spores can also adsorb a negatively charged cholesterol derivative, taurocholic acid. Furthermore, chitosan is amenable to chemical modifications, and, consistent with this property, dit1Δ spores can serve as a carrier for immobilization of enzymes. Given that yeast spores are a natural product, our results demonstrate that they, and especially dit1Δ mutants, can be used as chitosan beads and used for multiple purposes.

Biosorption of Elements

Biosorption is a unique ability of living or dead biomass to interact with substances such as metals where reduction of sorbate concentration can be achieved. Thus, it has been widely proposed as a promising alternative for metal remediation and recovery owing to its low cost and sustainable “green” nature. Despite considerable biosorption‐related research performed in the past few decades, no significant commercial success has been achieved so far. This chapter starts with discussion of the basic science of biosorption and the potential of some selected biomasses such as yeast, algae, agro‐based waste and vermicompost to be used as biosorbent material. Following this, some important issues regarding the practical application of biosorption are highlighted, including the advantages and disadvantages of using dead or living biomass, the availability of biosorption reactors, immobilization techniques, metal recovery and post‐treatment of spent biosorbent. Lastly, current challenges that limit the commercial success of biosorption as well as the direction of future research are discussed.

Cleanup of industrial effluents containing heavy metals: a new opportunity of valorising the biomass produced by brewing industry

Heavy metal pollution is a matter of concern in industrialised countries. Contrary to organic pollutants, heavy metals are not metabolically degraded. This fact has two main consequences: its bioremediation requires another strategy and heavy metals can be indefinitely recycled. Yeast cells of Saccharomyces cerevisiae are produced at high amounts as a by-product of brewing industry constituting a cheap raw material. In the present work, the possibility of valorising this type of biomass in the bioremediation of real industrial effluents containing heavy metals is reviewed. Given the auto-aggregation capacity (flocculation) of brewing yeast cells, a fast and off-cost yeast separation is achieved after the treatment of metal-laden effluent, which reduces the costs associated with the process. This is a critical issue when we are looking for an effective, eco-friendly, and low-cost technology. The possibility of the bioremediation of industrial effluents linked with the selective recovery of metals, in a strategy of simultaneous minimisation of environmental hazard of industrial wastes with financial benefits from reselling or recycling the metals, is discussed.

Detoxification of mycotoxins by probiotic preparation for broiler chickens

Biological decontamination of mycotoxins using microorganisms is one of the well known strategies for the management of mycotoxins in foods and feeds. Among the different potential decontaminating microorganisms,Saccharomyces cerevisiae and lactic acid bacteria represent unique groups, which are widely used in food fermentation and preservation. The aim of this study was to determine the influence of spontaneous fermentation with the use of probiotic bacteria and yeast (Lactobacillus paracasei/casei ŁOCK 0920,L. brevis ŁOCK 0944,L. plantarum ŁOCK 0945,Saccharomyces cerevisiae ŁOCK 0142), on reduction of sum of aflatoxines (B1, B2, G1, G2) and ochratoxin A concentration during fermentation and the microflora pattern during fermentaton. The probiotic bacteria and yeast applied creates a starter culture for flour fermentation that has a stable feature of detoxication of aflatoxines and especially ochratoxin A.

Bioremediation of industrial effluents containing heavy metals using brewing cells of Saccharomyces cerevisiae as a green technology: a review

The release of heavy metals into the environment, mainly as a consequence of anthropogenic activities, constitutes a worldwide environmental pollution problem. Unlike organic pollutants, heavy metals are not degraded and remain indefinitely in the ecosystem, which poses a different kind of challenge for remediation. It seems that the "best treatment technologies" available may not be completely effective for metal removal or can be expensive; therefore, new methodologies have been proposed for the detoxification of metal-bearing wastewaters. The present work reviews and discusses the advantages of using brewing yeast cells of Saccharomyces cerevisiae in the detoxification of effluents containing heavy metals. The current knowledge of the mechanisms of metal removal by yeast biomass is presented. The use of live or dead biomass and the influence of biomass inactivation on the metal accumulation characteristics are outlined. The role of chemical speciation for predicting and optimising the efficiency of metal removal is highlighted. The problem of biomass separation, after treatment of the effluents, and the use of flocculent characteristics, as an alternative process of cell-liquid separation, are also discussed. The use of yeast cells in the treatment of real effluents to bridge the gap between fundamental and applied studies is presented and updated. The convenient management of the contaminated biomass and the advantages of the selective recovery of heavy metals in the development of a closed cycle without residues (green technology) are critically reviewed.

Biosorption: a new rise for elemental solid phase extraction methods

Biosorption is a term that usually describes the removal of heavy metals from an aqueous solution through their passive binding to a biomass. Bacteria, yeast, algae and fungi are microorganisms that have been immobilized and employed as sorbents in biosorption processes. The binding characteristics of microorganisms are attributed to functional groups on the surface providing some features to the biosorption process like selectivity, specificity and easy release. These characteristics turn the biosorption into an ideal process to be introduced in solid phase extraction systems for analytical approaches. This review encompasses the research carried out since 2000, focused on the employment of biosorption processes as an analytical tool to improve instrumental analysis. Since aminoacids and peptides as synthetic analogues of natural metallothioneins, proteins present in the cell wall of microorganisms, have been also immobilized on solid supports (controlled pore glass, carbon nanotubes, silica gel polyurethane foam, etc.) and introduced into solid phase extraction systems; a survey attending this issue will be developed as well in this review.

Study of the mechanisms of Cu2+ biosorption by ethanol/caustic-pretreated baker's yeast biomass

Baker's yeast biomass was pretreated by ethanol and caustic soda, and then the pristine baker's yeast, ethanol pretreated baker's yeast (ethanol-baker's yeast) and caustic soda pretreated baker's yeast (caustic-baker's yeast) were utilized as biosorbents to adsorb Cu(2+) in aqueous solution. The influence of different parameters on Cu(2+) uptake by the three biomasses, such as initial Cu(2+) concentration, initial pH of solution, contact time and temperature, was studied. The mechanism of Cu(2+) binding by biomass was investigated by a number of techniques. Evidence from potentiometric titration revealed that the concentration of carboxyl and amino groups is higher on the caustic and ethanol-baker's yeast compared to the pristine baker's yeast and FTIR spectra confirmed carboxyl, and amino groups on the surface of baker's yeast could be available for characteristic coordination bonding with Cu(2+). In addition, SEM and Zeta potential of the three samples show that caustic and ethanol-pretreatment resulted in the change of baker's yeast surface structure and charge which is relative to adsorption. These results demonstrate that the increase of biosorption capacity for Cu(2+) by ethanol and caustic-baker's yeast was attributed to the increase and exposure of carboxyl and amino groups on the surface of biomass sample.

Interaction of malathion, an organophosphorus pesticide with Rhizopus oryzae biomass

Adsorption of malathion on Rhizopus oryzae biomass (ROB) with special reference to binding mechanism has been described. ROB has been found to adsorb approximately 85% of malathion from its aqueous solution as against 47-68% by other fungal biomasses. Hydrogen ion concentration does not influence the adsorption of malathion by ROB which follows Langmuir-Freundlich dual equilibrium isotherm model (r(2)=0.998). Both physical and chemical interactions are responsible for binding of malathion on ROB. Scanning electron micrographs and EDXA spectra exhibit adsorption of the pesticide on cell surface of ROB. Studies with cell surface polysaccharides show that chitosan through its amine groups contributes largely in the adsorption of malathion. Extraction of lipids from ROB decreases its adsorption capacity to the extent of 36.37-94.02%, depending on the polarity of the solvent.

Precipitation of Zn(II), Cu(II) and Pb(II) at bench-scale using biogenic hydrogen sulfide from the utilization of volatile fatty acids

Biological production of hydrogen sulfide (H(2)S) using sulfate-reducing bacteria (SRB) has important potential within environmental biotechnology. The aim of this work was to study the possibility of using SRB for the treatment of an acid mine drainage (AMD) at bench-scale. This process involved three stages: the optimization of H(2)S production through the utilization of total volatile fatty acids (TVFAs) by SRB, the establishment of a biofilm reactor for sulfide production, and the precipitation of metals by using the biologically produced H(2)S. The substrates used for TVFAs production consisted of papaya, apple and banana. The H(2)S produced from the degradation of TVFAs was utilized for the precipitation of a metal-contaminated effluent collected from Bolivar mine (Oruro, Bolivia). The maximum concentration of H(2)S obtained was approximately 16mM. Removal efficiencies of ca. 100% for copper, above 94% for zinc, and above 92% for lead were achieved.

Characteristics of copper tolerance in Yarrowia lipolytica

We discovered that a mutant strain of the dimorphic yeast Yarrowia lipolytica could grow in the yeast form in high concentrations of copper sulfate. The amount of metal accumulated by Y. lipolytica increased with increasing copper concentrations in the medium. Washing with 100 mM EDTA released at least 60% of the total metal from the cells, but about 20-25 micromol/g DW persisted, which represented about 30% of the soluble fraction of cultured cells. The soluble fraction (mainly cytosol) contained only about 10% of the total metal content within cells cultured in medium supplemented with 6 mM copper. We suggest that although a high copper concentration induces an efflux mechanism, the released copper becomes entrapped in the periplasm and in other parts of the cell wall. Washing with EDTA liberated not only copper ions, but also melanin, a brown pigment that can bind metal and which located at the cell wall. These findings indicated that melanin participates in the mechanism of metal accumulation. Culture in medium supplemented with copper obviously enhanced the activities of Cu, Zn-SOD, but not of Mn-SOD.

Biosorption of heavy metals by Saccharomyces cerevisiae: A review

Heavy metal pollution has become one of the most serious environmental problems today. Biosorption, using biomaterials such as bacteria, fungi, yeast and algae, is regarded as a cost-effective biotechnology for the treatment of high volume and low concentration complex wastewaters containing heavy metal(s) in the order of 1 to 100 mg/L. Among the promising biosorbents for heavy metal removal which have been researched during the past decades, Saccharomyces cerevisiae has received increasing attention due to the unique nature in spite of its mediocre capacity for metal uptake compared with other fungi. S. cerevisiae is widely used in food and beverage production, is easily cultivated using cheap media, is also a by-product in large quantity as a waste of the fermentation industry, and is easily manipulated at molecular level. The state of the art in the field of biosorption of heavy metals by S. cerevisiae not only in China, but also worldwide, is reviewed in this paper, based on a substantial number of relevant references published recently on the background of biosorption achievements and development. Characteristics of S. cerevisiae in heavy metal biosorption are extensively discussed. The yeast can be studied in various forms for different purposes. Metal-binding capacity for various heavy metals by S. cerevisiae under different conditions is compared. Lead and uranium, for instances, could be removed from dilute solutions more effectively in comparison with other metals. The yeast biosorption largely depends on parameters such as pH, the ratio of the initial metal ion and initial biomass concentration, culture conditions, presence of various ligands and competitive metal ions in solution and to a limited extent on temperature. An assessment of the isotherm equilibrium model, as well as kinetics was performed. The mechanisms of biosorption are understood only to a limited extent. Elucidation of the mechanism of metal uptake is a real challenge in the field of biosorption. Various mechanism assumptions of metal uptake by S. cerevisiae are summarized.

Isolation and process parameter optimization of Aspergillus sp. for removal of chromium from tannery effluent

Five morphologically different fungi were isolated from leather tanning effluent in which Aspergillus sp. and Hirsutella sp. had higher potential to remove chromium. The potential of Aspergillus sp. for removal of chromium was evaluated in shake flask culture in different pH, temperature, inoculums size, carbon and nitrogen source. The maximum chromium was removed at pH 6, temperature 30 degrees C, sodium acetate (0.2%) and yeast extract (0.1%). Aspergillus sp. was applied in 2l bioreactor for removal of chromium, and it was observed that 70% chromium was removed after 3 days.

Genome-wide screening of aluminum tolerance in Saccharomyces cerevisiae

Genome-wide screening has identified 37 Al-tolerance genes in Saccharomyces cerevisiae. These genes can be roughly categorised into three groups on the basis of function, i.e., genes related to vesicle transport processes, signal transduction pathways, and protein mannosylation. The largest group is composed of genes related to vesicle transport processes; severe Al sensitivity was found in yeast strains lacking these genes. The retrograde transport of endosome-derived vesicles back to the Golgi apparatus is an important factor in determining the Al tolerance of the vesicle transport system. The PKC1-MAPK cascade signalling pathway is important in the Al tolerance of signal transduction. The lack of the gene implicated in this process leads to weakened cell wall architecture, rendering the yeast Al-sensitive. Alternatively, Al might attack the cell wall and/or plasma membrane, and, as signalling is prevented in cells devoid of the genes related to signalling processes, the cells may be unable to alleviate the damage. The genes for protein mannosylation are also associated with Al tolerance, demonstrating the importance of cell wall architecture. These genes are involved in cell integrity processes.

Microorganisms in inorganic chemical analysis

There are innumerable strains of microbes (bacteria, yeast and fungi) that degrade or transform chemicals and compounds into simpler, safer or less toxic substances. These bioprocesses have been used for centuries in the treatment of municipal wastes, in wine, cheese and bread making, and in bioleaching and metal recovery processes. Recent literature shows that microorganisms can be also used as effective sorbents for solid phase extraction procedures. This review reveals that fundamental nonanalytical studies on the parameters and conditions of biosorption processes and on metal-biomass interactions often result in efficient analytical procedures and biotechnological applications. Some selected examples illustrate the latest developments in the biosorption of metals by microbial biomass, which have opened the door to the application of microorganisms to analyte preconcentration, matrix separation and speciation analysis.

Metal bioremediation through growing cells

Heavy-metal pollution represents an important environmental problem due to the toxic effects of metals, and their accumulation throughout the food chain leads to serious ecological and health problems. Metal remediation through common physico-chemical techniques is expensive and unsuitable in case of voluminous effluents containing complexing organic matter and low metal contamination. Biotechnological approaches that are designed to cover such niches have, therefore, received great deal of attention in the recent years. Biosorption studies involving low-cost and often dead/pretreated biomass have dominated the literature and, subsequently, extensive reviews focusing on equilibrium and kinetics of metal biosorption have also come up. However, the low binding capacity of biomass for certain recalcitrant metals such as Ni and failure to effectively remove metals from real industrial effluents due to presence of organic or inorganic ligands limit this approach. At times, when pure biosorptive metal removal is not feasible, application of a judicious consortium of growing metal-resistant cells can ensure better removal through a combination of bioprecipitation, biosorption and continuous metabolic uptake of metals after physical adsorption. Such approach may lead to simultaneous removal of toxic metals, organic loads and other inorganic impurities, as well as allow optimization through development of resistant species. However, sensitivity of living cells to extremes of pH or high metal concentration and need to furnish metabolic energy are some of the major constraints of employing growing cells for bioremediation. The efforts to meet such challenges via isolation of metal-resistant bacterial/fungal strains and exploitation of organic wastes as carbon substrates have began. Recent studies show that the strains (bacteria, yeast and fungi) isolated from contaminated sites possess excellent capability of metal scavenging. Some bacterial strains possess high tolerance to various metals and may be potential candidates for their simultaneous removal from wastes. Evidently, the stage has already been set for the application of metal-resistant growing microbial cells for metal harvesting. This review focuses on the applicability of growing bacterial/fungal/algal cells for metal removal and the efforts directed towards cell/process development to make this option technically/economically viable for the comprehensive treatment of metal-rich effluents.

Adhesion forces measured between a calcium blocker drug and its receptor in living cells using atomic force microscope

The adhesion force between the tip of an atomic force microscope cantilever derivatized with nimodipine (a calcium blocker, from the dihydropyridine class, currently used in clinical medicine for hypertension) and living cells of Saccharomyces cerevisiae (unicellular eukaryotes which portray ultrastructural features characteristic of higher eukaryotic cells) was measured. This methodology allowed us to locate (and visualize) pores on the cell surface which may be responsible for calcium transportation in the living cells. The interaction of the cantilever derivatized with the calcium blocker and a pore, which can be a calcium channel, is more intense than a non-derivatized cantilever and the pore. Outside the pore (on the rest of cell surface), a derivatized or a non-derivatized cantilever has the same pattern of adhesion force. The information obtained with this method is very important for the design of new, more potent and less toxic drugs for pharmacological use.

Thermal and spectroscopic studies on sorption of nickel(II) ion on protonated baker's yeast

Protonated form (Hy) of yeast was subjected to thermal analysis (TGA and DTG) in the temperature range 60-800 degrees C. Chemically bound water volatilizes around 200 degrees C and the matrix undergoes extensive oxidative decomposition at 450 degrees C, the weight loss reaching 75% at 800 degrees C. The sorption capacity of the matrix for nickel(II) ion increases on heat treatment from 60 to 200 degrees C (from 16.9 to 25.0 mg/g), but was reduced on heating to higher temperatures at an initial nickel(II) ion concentration of 1200 mg/g. The FTIR spectra of Hy and nickel(II) ion saturated yeast, indicated that biosorption occurs on the sugar and nucleic acid regions, possibly involving --COOH and --NH groups.