Cadmium removal using Cladophora in batch, semi-batch and flow reactors.

This study presents the results of using viable algae to remove cadmium from a synthetic wastewater. In batch and semi-batch tests, a local strain of Cladophora algae removed 80-94% of the cadmium introduced. The flow experiments that followed were conducted using non-local Cladophora parriaudii. Results showed that the alga removed only 12.7(+/-6.4)% of the cadmium introduced into the reactor. Limited removal was the result of insufficient algal quantities and poor contact between the algae and cadmium solution.     

Cadmium(II) Removal by a Hyperaccumulator Fungus <Emphasis Type="Italic">Phoma</Emphasis> sp. F2 Isolated from Blende Soil

A cadmium(II)-resistant fungus, strain F2, isolated from blende soil was identified as Phoma sp. by morphological study and internal transcribed spacer sequencing. This strain could accumulate 280 mg of Cd(II)/g dry weight mycelium. In liquid medium containing 163.8 mg Cd(II)/L, 96% of Cd(II) was removed by the actively growing mycelium. In addition, both oven-dried and lyophilized mycelium could effectively adsorb Cd(II). There were removed 91% and 46.2% of Cd(II) from 51.6 mg Cd(II)/L solution by lyophilized biomass and oven-dried biomass respectively. Transmission electron microscopy and energy-dispersive X-ray analysis showed the accumulation of Cd(II) in the mycelium cell walls. Our results demonstrated that Phoma sp. F2 was a hyperaccumulator for the removal of Cd(II) from contaminated soil and water.     

Removal of cadmium from scallop hepatopancreas by microbial processes

A microbial process for removing cadmium from a homogenate of hepatopancreas, a waste of scallop processing, was devised to use this waste for value-added protein resources. Microorganisms were screened on the basis of the ability to remove cadmium from a medium with the initial concentration of 10 mg/l of cadmium. One soil isolate, identified as Xanthomonas sp. UR No. 2 by its taxonomical characteristics, removed 98% of the cadmium in the medium in 2 d. During cultivation of this strain in the homogenates of hepatopancreas digested by endopeptidases, 90% of cadmium was removed, while this strain had little effect on the simple non-digested homogenates. The mass balance of cadmium during homogenizations of the hepatopancreas tissues and cultivations in the protease-treated homogenate were examined. The content of crude proteins of culture supernatant treated by Xanthomonas sp. UR No. 2 was equivalent to those of various feedstuffs on the market.     

Two models for screening chelating agents for cadmium removal

The effectiveness of some chelating agents to mobilize cadmium from Chinese hamster ovary cells after chronic exposure (20 hr), as well as from cytosolic metallothionein, was studied. In the first protocol, the most effective substance was 2,3-dimercaptopropanol, followed by 2,3-dimercaptopropane-1-sulfonate and 2,3-dimercaptosuccinic acid, whereas CaNa₃3-diethylenetriamine pentaacetic acid × 5H₂O showed less effect. Simultaneous incubation of cells with cadmium and the chelating agent resulted in a different order of effectiveness: CaNa₃ DTPA prevented cadmium uptake almost totally, 2,3-mercaptopropanol by 75% and 2,3-dimercaptopropane-1-sulfonate by 35%. Neither CaNa₃-diethylenetriamine pentaacetic acid × 5H₂O nor 2,3-dimercaptosuccinic acid had altered the distribution of cadmium between the cytosolic protein fractions after a 2 hr incubation of cells, whereas after this period, 2,3-dimercaptopropanol had removed all cadmium from metallothionein, and 2,3-dimercaptopropane-1-sulfonate about 50%. None of the chelating agents had reduced the amount of Cd bound to high molecular weight proteins. In the cell free system, 2,3-dimercaptopropanol and 2,3-dimercaptopropane-1-sulfonate were equally effective and removed all cadmium from metallothionein within ten minutes. CaNa₃-diethylenetriamine pentaacetic acid × 5H₂O, however, even after 60 min, had removed only 50% of the cadmium. The remaining cadmium was found distributed to the high molecular weight and lower molecular weight protein fractions.Abbreviations BAL 2,3-dimercaptopropanol - CHO Chinese hamster ovary cells - DMPS 2,3-dimercaptopropane-1-sulfonate - DMSA 2,3-dimercaptosuccinic acid - DTPA CaNa₃-diethylenetriaminepentaacetic acid × 5 H₂O - HMW proteins high molecular weight proteins - MT metallothionein     

Aerobic sulfide production and cadmium precipitation by Escherichia coli expressing the Treponema denticola cysteine desulfhydrase gene

The cysteine desulfhydrase gene of Treponema denticola was over-expressed in Escherichia coli to produce sulfide under aerobic conditions and to precipitate metal sulfide complexes on the cell wall. When grown in a defined salts medium supplemented with cadmium and cysteine, E. coli producing cysteine desulfhydrase secreted sulfide and removed nearly all of the cadmium from solution after 48 h. A control strain produced significantly less sulfide and removed significantly less cadmium. Measurement of acid-labile sulfide and energy dispersive X-ray spectroscopy indicated that cadmium was precipitated as cadmium sulfide. Without supplemental cysteine, both the E. coli producing cysteine desulfhydrase and the control E. coli demonstrated minimal cadmium removal.     

Antiviral efficacy of bromo-anilino substituents of 4,5-dihydrofuran-3-carboxylate compound CW-33 against Japanese encephalitis virus

Japanese encephalitis virus (JEV), a mosquito-borne flavivirus, occasionally causes severe central nervous system disorders in the risk zone where more than 3 billion people reside. Our prior studies demonstrated antiviral potential of 4,5-dihydrofuran-3-carboxylate compound CW-33 (ethyl 2-(3′,5′-dimethylanilino)-4-oxo-4,5-dihydrofuran-3-carboxylate) and its derivative CW-33A ((ethyl 2-(2-fluoroanilino)-4-oxo-4,5-dihydrofuran-3-carboxylate) against JEV infection ((Int. J. Mol. Sci. 2016, 17: E1386; Sci. Rep. 2018, 8: 16595). This study synthesized six new CW-33 derivatives containing chloro, or bromo groups at the C-2, C-3, or C-4 of anilino ring of CW-33, and assessed the antiviral activity and mechanisms of these chloro- and bromo-anilino substituted derivatives. CW-33K, CW-33L and CW-33M had the bromo-substituents at the C-2, C-3, or C-4 of anilino ring of CW-33, respectively, showing the higher anti-JEV activity than CW-33 and other derivatives. CW-33K (ethyl 2-(2-bromoanilino)-4-oxo-4,5-dihydrofuran-3-carboxylate) exhibited the highest antiviral efficacy and therapeutic index. The IC50 value of CW-33K was less than 5 μM for reducing JEV-induced cytopathic effect, virus infectivity and virus yield. CW-33K significantly inhibited the JEV replication at the early and late stages, suppressing viral RNA synthesis and intracellular JEV particle production. The study demonstrated that the CW-33 derivative with a bromo substitution at the C-2 anilino ring improved the antiviral activity JEV, providing the structure-antiviral activity relationship for the development of anti-JEV agents.     

Interplay of the Czc system and two P-type ATPases in conferring metal resistance to Ralstonia metallidurans

Cadmium and zinc are removed from cells of Ralstonia metallidurans by the CzcCBA efflux pump and by two soft-metal-transporting P-type ATPases, CadA and ZntA. The czcCBA genes are located on plasmid pMOL30, and the cadA and zntA genes are on the bacterial chromosome. Expression of zntA from R. metallidurans in Escherichia coli predominantly mediated resistance to zinc, and expression of cadA predominantly mediated resistance to cadmium. Both transporters decreased the cellular content of zinc or cadmium in this host. In the plasmid-free R. metallidurans strain AE104, single gene deletions of cadA or zntA had only a moderate effect on cadmium and zinc resistance, but zinc resistance decreased 6-fold and cadmium resistance decreased 350-fold in double deletion strains. Neither single nor double gene deletions affected zinc resistance in the presence of czcCBA. In contrast, cadmium resistance of the cadA zntA double mutant could be elevated only partially by the presence of CzcCBA. lacZ reporter gene fusions indicated that expression of cadA was induced by cadmium but not by zinc in R. metallidurans strain AE104. In the absence of the zntA gene, expression of cadA occurred at lower cadmium concentrations and zinc now served as an inducer. In contrast, expression of zntA was induced by both zinc and cadmium, and the induction pattern did not change in the presence or absence of CadA. However, expression of both genes, zntA and cadA, was diminished in the presence of CzcCBA. This indicated that CzcCBA efficiently decreased cytoplasmic cadmium and zinc concentrations. It is discussed whether these data favor a model in which the cations are removed either from the cytoplasm or the periplasm by CzcCBA.     

Chlorella sorokiniana immobilized on the biomatrix of vegetable sponge of Luffa cylindrica: a new system to remove cadmium from contaminated aqueous medium

A new sorption system of microalgal cells immobilized on the biostructural matrix of Luffa cylindrica for sequestering cadmium is reported. Free and immobilized Chlorella sorokiniana removed cadmium from 10 mgl(-1) solution at the efficiency of 92.7% and 97.9% respectively. Maximum cadmium sorption was observed to be 39.2 mgg(-1) at equilibrium (C(eq)) of 112.8 mgl(-1) by immobilized microalgal biomass as compared to 33.5 mgg(-1) at C(eq) of 116.5 mgl(-1) by free biomass from initial concentration of 150 mgl(-1). In continuous liquid flow column, the cadmium sorption capacity of immobilized C. sorokiniana was 192 mgg(-1), which was 73.2% of the total metal passed in 51.5 l. Metal desorption with 0.1 M HCl was 100% and the desorbed immobilized system was reusable with a similar efficiency in the subsequent cycle.     

Potent heterologous antifungal proteins from cheeseweed (Malva parviflora)

Two novel antifungal proteins were purified and characterized from cheeseweed (Malva parviflora). Both proteins, designated CW-1 and CW-2, are composed of two different subunits of 5000 and 3000 Da, respectively. These proteins possess very potent antifungal activities, and more interestingly the inhibition is fungicidal instead of fungistatic. At low salt condition, the IC(50) of CW-1 and CW-2 against Fusarium graminearum (Fg) is 2.5 ppm. At high salt condition which diminishes the antifungal activity of many antifungal proteins, both CW-1 and CW-2 still maintain potent activity against Fg with IC(50) of 10 ppm. The two subunits could be separated by gel filtration in the presence of 6 M urea, but their antifungal activity cannot be recovered after the removal of urea. Amino acid sequence analysis indicates that both subunits of CW-1 show homology to 2S albumin, whereas the two subunits of CW-2 have homology to vicilin protein from cotton. To our knowledge, this is the first report of isolation and characterization of heterologous antifungal proteins from any source.     

The effect of superoxide dismutase deficiency on cadmium stress

Saccharomyces cerevisiae mutant strains deficient in superoxide dismutase (Sod), an antioxidant enzyme, were used to analyze cadmium absorption and the oxidation produced by it. Cells lacking the cytosolic Sod1 removed twice as much cadmium as the control strain, while those deficient in the mitochondrial Sod2 exhibited poor metal absorption. Interestingly, the sod1 mutant did not become more oxidized after exposure to cadmium, as opposed to the control strain. We observed that the deficiency of Sod1 increases the expression of both Cup1 (a metallothionein) and Ycf1 (a vacuolar glutathione S-conjugate pump), proteins involved with protection against cadmium. Furthermore, when sod1 cells were exposed to cadmium, the ratio glutathione oxidized/glutathione reduced did not increase as expected. We propose that a high level of metallothionein expression would relieve glutathione under cadmium stress, while an increased level of Ycf1 expression would favor compartmentalization of this metal into the vacuole. Both conditions would reduce the level of glutathione-cadmium complex in cytosol, contributing to the high capacity of absorbing cadmium by the sod1 strain. Previous results showed that the glutathione-cadmium complex regulates cadmium uptake. These results indicate that, even indirectly, metallothionein also regulates cadmium transport.     

Cadmium removal by living cells of the marine microalga Tetraselmis suecica

Cadmium removal by living cells of the marine microalga Tetraselmis suecica was tested in cultures exposed to different cadmium concentrations (0.6, 3, 6, 15, 30 and 45 mg/l). The EC50 for growth was 7.9 mg Cd/l after six days of exposure. The cadmium removed was proportional to the concentration of this metal in the medium and it was dependent on the time of exposure; cultures with higher cadmium concentration removed a higher amount of this metal. In cultures exposed to 0.6 mg/l, T suecica cells removed 98.1% of added cadmium with 0.392 x 10(-6) microg Cd/cell, whereas in cultures with 45 mg/l only 7.7% was removed with 16.052 x 10(-6) microg Cd/cell. The highest amount of cadmium removed per liter of culture was observed in cultures exposed to 6 mg/l, with 3.577 mg/l of cadmium. After six days of incubation, the higher proportion of cadmium was bioaccumulated intracellularly in all cultures except in 45 mg/l cultures, the percentage of intracellular cadmium being always more than 50%. The highest percentage of bioadsorbed cadmium (60.1%) was found in cells of cultures with the highest cadmium concentration (45 mg/l). Furthermore, a relation between intracellular cadmium and the concentration of sulfhydryl groups was observed.     

Adaptation strategies of two closely related Desmodesmus armatus (green alga) strains contained different amounts of cadmium: A study with light-induced synchronized cultures of algae

During the Desmodesmus armatus cell cycle, 8-celled coenobia of 276-4d strain accumulated a much lower amounts of cadmium than unicells of B1-76 strain. Cadmium reduced growth and photosynthesis in the cells of strain B1-76, but not those of 276-4d strain. Cells of 276-4d strain revealed a higher activity of superoxide dismutase (SOD) isoforms, in particular the activity and protein content of Fe-SOD. Cu/Zn-SOD was earlier and much stronger induced by cadmium in 276-4d than in B1-76 strain, whereas Fe- and Mn-SOD activity and Fe-SOD synthesis were induced only in 276-4d strain. Cadmium did not affect the heat shock protein 70 synthesis in B1-76 strain, but significantly stimulated this process in 276-4d strain. The level of glutathione increased 30-fold during cell development of Cd-exposed 276-4d strain, while in B1-76 it increased about 12 timed. Matured cells of both strains exposed to cadmium produced comparable amounts of phytochelatins and other thiol peptides, but their production in young cells of B1-76 strain was much higher than in 276-4d strain. In conclusion, a complex of internal detoxification mechanisms appeared to be more efficient in cells of 276-4d strain than B1-76 one.     

一株高耐镉硫酸盐还原菌的分离及脱硫性能研究

本研究从镉污染稻田水稻根际土壤中分离、纯化出一株硫酸盐还原菌SRB1-1,并对该菌株的生理生态特征、镉和盐耐受性、16S rDNA、脱硫性能及影响因子进行了系列分析。结果表明,该菌为革兰氏阴性菌,菌体弧状,对镉离子的耐受浓度可达200 mg/L,在2%的氯化钠浓度下仍可生长。对其16S rDNA的序列分析表明该菌株属于脱硫弧菌属(Desulfovibrio)。单因子实验考察温度、pH及SO_4~(2-)浓度对该菌脱硫效率的影响,正交实验确定了该菌最佳脱硫工艺条件及影响因子顺序。结果表明最佳脱硫工艺条件为pH 7.5、温度40℃、SO_4~(2-)浓度为1 000 mg/L、培养时间56 h。     

Heavy metal accumulation by immobilized cells of a Citrobacter sp.

Summary Immobilized cells of a strain of a Citrobacter sp. were effective in the removal of cadmium, lead and copper from single and mixed metal flows, and from synthetic effluents. About 80% of the presented metal was removed, and this was increased to nearly 100% by the incorporation of additional immobilized cell column units.     

镉对固定化小球藻除磷效果的影响

采用人工配制污水进行静态模拟实验,研究了镉对被海藻酸钙凝胶包埋固定的小球藻去除磷能力的影响.结果表明:在各光照及pH条件下,镉对固定化小球藻吸收磷的效果随着实验时间的推移而变化,在实验的第一天时影响最大;总体而言,镉抑制了固定化小球藻的除磷能力,但在某些条件下镉反而提高了藻对磷的吸收;固定化处理减弱了镉对小球藻除磷能力的影响.具体的光照、pH值与镉的影响效果的关系尚待进一步探讨.     

Immobilization of blue green microalgae on loofa sponge to biosorb cadmium in repeated shake flask batch and continuous flow fixed bed column reactor system

Summary An indigenous strain of blue green microalga, Synechococcus sp., isolated from wastewater, was immobilized onto loofa sponge discs and investigated as a potential biosorbent for the removal of cadmium from aqueous solutions. Immobilization has enhanced the sorption of cadmium and an increase of biosorption (21%) at equilibrium was noted as compared to free biomass. The kinetics of cadmium biosorption was extremely rapid, with (96%) of adsorption within the first 5 min and equilibrium reached at 15 min. Increasing initial pH or initial cadmium concentration resulted in an increase in cadmium uptake. The maximum biosorption capacity of free and loofa immobilized biomass of Synechococcus sp. was found to be 47.73 and 57.76 mg g⁻¹ biomass respectively. The biosorption equilibrium was well described by Langmuir adsorption isotherm model. The biosorbed cadmium was desorbed by washing the immobilized biomass with dilute HCl (0.1 M) and desorbed biomass was reused in five biosorption–desorption cycles without an apparent decrease in its metal biosorption capacity. The metal removing capacity of loofa immobilized biomass was also tested in a continuous flow fixed-bed column bioreactor and was found to be highly effective in removing cadmium from aqueous solution. The results suggested that the loofa sponge-immobilized biomass of Synechococcus sp. could be used as a biosorbent for an efficient removal of heavy metal ions from aqueous solution.     

Effect of water activity on invertase production in solid state fermentation by improved diploid strains of Aspergillus niger

Invertase production under solid state fermentation (SSF) was determined using two overproducing mutants (Aw96-3 and Aw96-4) isolated previously from the wild type strain Aspergillus niger C28B25, as well as one diploid (DAR1) and two autodiploid strains (AD96-3 and AD96-4) constructed by parasexual crossings among these mutants. Using polyurethane foam (PUF) as an inert carrier, two initial water activity (Aw) values were evaluated (0.99 and 0.96). At Aw=0.99, maximal activity was reached by diploid AD96-4 (48.91 IU/ml) representing 30- and 13-fold increases with respect to maximal values achieved by the wild type and the haploid parental mutant (Aw96-4), respectively. Similar levels were achieved by this strain at Aw=0.96. However, diploid DAR1 only produced high levels of invertase at Aw=0.96 (43.90 IU/ml), whereas strain AD96-3 reached its highest production (31.10 IU/ml) at Aw=0.99. Both productivity and yields were also analysed for every strain at each Aw value.     

Dual-bioaugmentation strategy to enhance remediation of cocontaminated soil.

Although metals are thought to inhibit the ability of microorganisms to degrade organic pollutants, several microbial mechanisms of resistance to metal are known to exist. This study examined the potential of cadmium-resistant microorganisms to reduce soluble cadmium levels to enhance degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) under conditions of cocontamination. Four cadmium-resistant soil microorganisms were examined in this study. Resistant up to a cadmium concentration of 275 microg ml(-1), these isolates represented the common soil genera Arthrobacter, Bacillus, and Pseudomonas. Isolates Pseudomonas sp. strain H1 and Bacillus sp. strain H9 had a plasmid-dependent intracellular mechanism of cadmium detoxification, reducing soluble cadmium levels by 36%. Isolates Arthrobacter strain D9 and Pseudomonas strain I1a both produced an extracellular polymer layer that bound and reduced soluble cadmium levels by 22 and 11%, respectively. Although none of the cadmium-resistant isolates could degrade 2,4-D, results of dual-bioaugmentation studies conducted with both pure culture and laboratory soil microcosms showed that each of four cadmium-resistant isolates supported the degradation of 500-microg ml(-1) 2,4-D by the cadmium-sensitive 2,4-D degrader Ralstonia eutropha JMP134. Degradation occurred in the presence of up to 24 microg of cadmium ml(-1) in pure culture and up to 60 microg of cadmium g(-1) in amended soil microcosms. In a pilot field study conducted with 5-gallon soil bioreactors, the dual-bioaugmentation strategy was again evaluated. Here, the cadmium-resistant isolate Pseudomonas strain H1 enhanced degradation of 2,4-D in reactors inoculated with R. eutropha JMP134 in the presence of 60 microg of cadmium g(-1). Overall, dual bioaugmentation appears to be a viable approach in the remediation of cocontaminated soils.     

Gas vesicles are strengthened by the outer-surface protein,GvpC

The critical collapse pressure of gas vesicles isolated from Anabaena flos-aquae decreased from 0.557 to 0.190 MPa when GvpC, the hydrophilic 22 kDa protein present on the outer surface of the gas vesicle, was removed by rising in 6 M urea. Recombinant GvpC was purified from inclusion bodies, produced in an E. coli strain containing an expression vector bearing the gene ecoding GvpC from A. flos-aquae, and then solubilised in 6 M urea. This recombinant GvpC became bound to gas vesicles that had been stripped of their native protein, when the urea was removed by dialysis; the amount which bound increased with the concentration of GvpC present. The critical pressure of these reconstituted gas vesicles increased to 0.533 MPa, 96% of the original value. These results indicate that the function of GvpC is to increase the strength of the structure.Non-standard abbreviations SBTI Soy bean trypsin inhibitor - Gvp Gas vesicle protein - SDS Sodium dodecyl sulphate - PAGE Polyacrylamide gel electrophoresis