Flocculation properties of pectin in various suspensions

Pectin had a flocculating activity and its flocculating activities in various suspensions were investigated. Flocculating activity of pectin in a kaolin suspension was markedly stimulated by the addition of Al3+ and Fe3+ to the suspension. Optimum temperature for flocculating activity of pectin in the kaolin suspension was around 30 degrees C and high flocculating activity was obtained when 30 mg/l of pectin and 0.2 mM Fe3+ were added to the suspension. Other inorganic suspensions of activated carbon and acid clay were flocculated by pectin in the presence of Al3+ or Fe3+. Flocculation of organic suspensions such as cellulose and yeast by pectin occurred when 0.1-0.2 mM Fe3+ was present in the suspensions.     

Characterization of a compound bioflocculant produced by mixed culture of <Emphasis Type="Italic">Rhizobium radiobacter</Emphasis> F2 and <Emphasis Type="Italic">Bacillus sphaeicus</Emphasis> F6

A compound bioflocculant CBF-F26, produced by mixed culture of Rhizobium radiobacter F2 and Bacillus sphaeicus F6, was investigated with regard to its physicochemical and flocculating properties. It was identified as a polysaccharide bioflocculant composed of rhamnose, mannose, glucose, and galactose, respectively, in a 1.3: 2.1: 10.0: 1.0 molar ratio. The average molecular weight was determined as 4.79 × 10⁵ Da by gel-permeation chromatography. Infrared spectrum and X-ray photoelectron spectroscopy revealed the presence of carboxyl, hydroxyl and amino groups in its structure. Thermostability test suggested that CBF-F26 was thermostable and high flocculating activity was maintained. Thermogravimetric property, intrinsic viscosity and surface morphology of CBF-F26 were also studied. CBF-F26 was effective under neutral and weak alkaline conditions (pH 7.0–9.0), and flocculating activities of higher than 90% were obtained in the concentration range of 8–24 mg l⁻¹ at pH 8.0. The flocculation could be stimulated by cations Ca²⁺, Zn²⁺, Fe²⁺, Al³⁺, and Fe³⁺. In addition, the probable flocculation mechanisms were proposed.     

Characteristics of extracellular polymeric substances (EPS) fractions from excess sludges and their effects on bioflocculability

Extracellular polymeric substances (EPS) of biological origin are ubiquitous in excess sludges and can be applied as an underlying bioflocculant, owing to their high content of macromolecules and cations. However, low flocculating activity limits the feasibility of their practical applications. This study provides a novel EPS fractionation approach to improve their flocculability by extracting an active EPS fraction and removing the others with low flocculability. The results showed that for two excess sludges (called sludge A and sludge B), the tightly bound EPS (TB-EPS) fraction possessed a high flocculating rate to kaolin suspension compared with the other EPS fractions [i.e., supernatant, slime, and loosely bound EPS (LB-EPS) fraction] (>54.1 ± 1.4% vs <7.8 ± 1.6%). High bioflocculability of TB-EPS fraction could be attributable to high contents of macromolecules (330–1200 kDa) and trivalent cations (Fe³⁺ and Al³⁺). Further investigation reveals that the TB-EPS fraction caused aggregation of particles by bridging and sweep flocculation.     

Characterization of bioflocculant MBF3-3 produced by an isolated <Emphasis Type="Italic">Bacillus </Emphasis>sp.

Summary  The characteristics of bioflocculant MBF3-3 produced by Bacillus sp. BF3-3 were investigated here. MBF3-3 showed excellent flocculating activity on real and synthetic wastewaters, and consumed a much lower dosage than that of the widely used polyaluminum chloride (PAC) when flocculating brewery wastewater. Except Fe³⁺, metal ions, including Al³⁺, Mg²⁺, Ca²⁺, K⁺ and Na⁺, can stimulate the flocculating activity of MBF3-3 obviously, and the stimulating effects increased in the order: monovalent < bivalent < trivalent. MBF3-3 was mainly composed of acidic polysaccharide (66.1%) and protein (29.3%), in which acidic polysaccharide was the main effective flocculating component. OH and COO– groups may play a vital role in the flocculation of suspended particles.     

Characterization of a bioflocculant produced by the marine myxobacterium Nannocystis sp. NU-2

The marine myxobacterium strain NU-2, which can grow on high concentrations (up to 7%) of NaCl, was isolated from a salt soil sample collected from the coast of the Huanghai Sea, China. Morphological properties and 16S rDNA sequence analysis indicated that the isolate is a novel species related to the genus Nannocystis. Nannocystis sp. NU-2 produced a new kind of flocculating substance in a starch medium with a yield of 14.8 g l^–1. The NU-2 flocculant was composed of 40.3% proteins and 56.5% polysaccharides, of which glucose, mannose and glucuronic acid were the principal constituents in the relative proportions of 5:4:1. The flocculation activity of the NU-2 flocculant depends strongly on cations such as Fe³⁺ and Al³⁺. When a 30 mg l^–1 FeCl₃ solution is present in kaolin clay suspension, 30 mg l^–1of the flocculant produced a high flocculating activity value of 90%, which remained unchanged over an extensive pH range (pH 2.0–13.0). The flocculant was tested for its ability to bleach dyeing liquors, and the bleaching activities were 98.2% for acid red in 100 mg l^–1of the flocculant and 99.0% for direct emerald blue in 50 mg l^–1of the flocculant under test conditions. Use of the flocculant to bleach basic pink and cation emerald blue liquors was not effective. Electronic Publication     

Characteristics of a biopolymer flocculant produced by Bacillus sp. PY-90

A biopolymer flocculant-producing bacterium, strain PY-90, was isolated and considered to belong to Bacillus subtilis. For the production of biopolymer flocculant by strain PY-90, a medium containing 2 to 5% l-glutamic acid as a nitrogen source was suitable. The biopolymer flocculant was a homopolymer composed of glutamic acid residues and was presumed to be poly(γ-glutamic acid). In kaolin suspension, the highest flocculating activity was attained at the biopolymer flocculant concentration of 20 mg/l. The flocculating activity was increased by the addition of Ca²⁺, and the optimum concentration of which was about 2 to 8 mM. The flocculating activity was high in an acidic pH range of 3.0 to 5.0, and decreased upon heating at 100°C.     

Characteristics and flocculating mechanism of a novel bioflocculant HBF-3 produced by deep-sea bacterium mutant Halomonas sp. V3a’

A novel bioflocculant HBF-3 produced by deep-sea bacterium mutant Halomonas sp. V3a’ was investigated with regard to its flocculating characteristics and mechanism. 4.0 m g l⁻¹ HBF-3 showed the maximum flocculating activity of 96.9% in 5.0 g l⁻¹ Kaolin suspension containing 11.25 mM CaCl₂, and that its flocculating activity was more than 90% within 5–40°C and over 80% in a wide pH range (3.0–11.0). Chemical analyses indicated that the biopolymer HBF-3 was mainly a polysaccharide, including neutral sugar residues (20.6%), uronic acid residues (7.6%), amino sugar residues (1.6%) and sulfate groups (5.3%). Fourier transform infrared (FTIR) spectrum showed the presence of carboxyl and hydroxyl groups in HBF-3 molecular. The average molecular mass of HBF-3, as determined by gel filtration chromatography (GFC), was approximately 590 kDa. Flocculation of Kaolin suspension with HBF-3 acted as a model to explore the flocculating mechanism in which bridging mediated by Ca²⁺ was proposed as the primary action based upon the experimental observations.     

Bioconversion of lignocellulose and simultaneous production of cellulase,ligninase and bioflocculants by Alcaligenes faecalis-X3

Lignocelluloses have been used as carbon sources for bioflocculant production. However, the low bioconversion efficiency of lignocellulose to bioflocculants is a major challenge. In this study, a lignocellulolytic strain of Alcaligenes faecalis-X3 was cultivated in ramie bio-degumming wastewater. Optimal production of ligninase, cellulase and bioflocculants (MBF-X3) was evaluated. The highest activity of MBF-X3 under the optimal conditions of pH 6.0 at 48 h of fermentation was 95.44%, with the maximum production of ligninase and cellulase (0.27 and 0.12 U/mL, respectively). The crude ligninase and cellulase had optimum activities at pH 5.0 and 40 °C and pH 6.0 and 50 °C, respectively. The cellulase activity was increased by Mn²⁺, Ca²⁺, Zn²⁺, and Mg²⁺ at 1 mM. The ligninase activity was significantly enhanced in the presence of Zn²⁺ at 10 mM. The flocculating activity of MBF-X3 was not changed by the addition of any metal cation. The results demonstrated that A. faecalis possesses an excellent enzyme system for the efficient bioconversion of lignocellulose into MBF-X3. Additionally, MBF-X3 has a high flocculating efficiency of Disperse Blue-2BLN (85.7%) at a dose of 1.0 g/L.     

Action of ferric and aluminium ions on the dormancy breakage of <Emphasis Type="Italic">Stylosanthes humilis</Emphasis> seeds

Dormancy of scarified seeds of Stylosanthes humilis was broken by acidic Al³⁺ and Fe³⁺ solutions. Fe⁺³-stimulated seeds exhibited a high activity of 1-aminocyclopropane-1-carboxylate (ACC) oxidase and produced great amounts of ethylene, which showed correlated with the germination process. In addition, specific inhibitors of ethylene biosynthesis and action largely depressed the Fe³⁺-stimulated germination, leading to the conclusion that the ion broke dormancy by triggering ethylene production by the seeds. By contrast, inhibitors of ethylene biosynthesis and action did not impair germination of Al³⁺-stimulated dormant seeds. Moreover, ethylene production and activity of ACC oxidase of Al³⁺-treated seeds was substantially decreased by inhibitors of ethylene biosynthesis, but germination kept large. Together these data suggest that ethylene biosynthesis was not required in the chain of events triggered by Al³⁺ leading to dormancy breakage. Methyl viologen (MV), a reactive oxygen species-generating compound, broke dormancy of seeds to the same extent as Al³⁺ did. Germination of both Al³⁺- and MV-stimulated dormant seeds was inhibited by sodium selenate, an antioxidant compound; selenate, however had no effect on germination of Fe³⁺-stimulated seeds. Together these data indicate that the mechanisms underlying the germination of Al³⁺- and Fe³⁺-treated seeds are not the same.     

Characterization and in vitro selection for iron efficiency inPyrus andCydonia

Summary Responses to low Fe were characterized in tissue cultures ofPyrus amygdaliformis andCydonia oblonga (quince), two species used as rootstocks for pear. Cultured shoots and plantlets ofP. amygdaliformis had a higher chlorophyll concentration and Fe²⁺/total Fe ratio than those ofC. oblonga when grown under low Fe conditions. This tolerance to low Fe was correlated with high Fe³⁺-reducing ability and medium acidification. The adaptive responses were manifested in roots of plantlets, shoot bases, root cultures, and cell suspension cultures. Shoots were regenerated from leaves of quince and subjected to Fe-deficient conditions. Two somaclonal variants (IE-1 and IE-2) were recovered; each displayed higher ability to reduce Fe³⁺ and acidify the medium. These variants may be useful as rootstocks for regions with calcareous soils, which limit Fe availability.     

Factors affecting lipid peroxidation in guinea-pig adrenal microsomes

Studies were carried out to examine the effects of and interactions between NADPH, Fe²⁺, Fe³⁺ and ascorbate on lipid peroxidation in guinea-pig adrenal microsomes. Fe²⁺, at levels between 10⁻⁶ and 10⁻³ M, produced concentration-dependent increases in lipid peroxidation in adrenal microsomes; Fe²⁺ had a far greater effect than Fe³⁺. In liver microsomes, by contrast, Fe²⁺ and Fe³⁺ had quantitatively similar effects on lipid peroxidation. NADPH alone had no effect on malonaldehyde production by adrenal microsomes. However, in the presence of low Fe²⁺ concentrations (10⁻⁶ M), NADPH stimulated malonaldehyde production; the stimulation was not demonstrable in microsomes which had been heat-treated to inactive microsomal enzymes. In the presence of high Fe²⁺ levels (10⁻³ M), NADPH produced a concentration-dependent inhibition of lipid peroxidation; the inhibition was fully demonstrable in heat-treated microsomes. In the presence of Fe³⁺ (10⁻⁶ to 10⁻³ M), NADPH had little effect on lipid peroxidation, suggesting that NADPH does not significantly promote the reduction of Fe³⁺ to Fe²⁺ in adrenal microsomes. Ascorbate alone increased malonaldehyde production by adrenal microsomes; maximum stimulation occurred at a concentration of 10⁻⁴ M. Ascorbate-induced lipid peroxidation was also inhibited by NADPH. Ascorbate (5 · 10⁻⁶ to 1 · 10⁻⁴ M) synergistically interacted with low levels (10⁻⁶ M) of Fe²⁺ to enhance malonaldehyde production by adrenal microsomes. The synergism was not demonstrable at high concentrations (10⁻³ M) of Fe²⁺ At all concentrations (10⁻⁶ to 10⁻³ M) of Fe³⁺ studied, ascorbate synergistically increased the production of malonaldehyde. The results indicate that interactions between various endogenous substances may be important in the control of adrenal microsomal lipid peroxidation and that there are differences in the regulation of adrenal and hepatic lipid peroxidation.     

Production of a biopolymer flocculant from Bacillus licheniformis and its flocculation properties

Bacillus licheniformis CCRC 12826 produced extracellularly an excellent biopolymer flocculant in a large amount when it was grown aerobically in a culture medium containing citric acid, glutamic acid and glycerol as carbon sources. The biopolymer flocculant was an extremely viscous material with a molecular weight over 2 x 10(6) by gel permeation chromatography. It could be easily purified from the culture medium by ethanol precipitation. It was shown to be a homopolymer of glutamic acid by amino acid analysis and thin layer chromatography and presumed to be poly-glutamic acid (PGA). This bioflocculant efficiently flocculated various organic and inorganic suspensions. It flocculated a suspended kaolin suspension without cations, although its flocculating activity was synergistically stimulated by the addition of bivalent or trivalent cations Ca2+, Fe3+ and Al3+. However, the synergistic effects of metal cations were most effective at neutral pH ranges. The comparison of the flocculating activity between the present biopolymer and a commercial lower molecular weight product showed that the biopolymer of the present study had much higher activity. The high productivity and versatile applications of PGA make its development as a new biodegradable, harmless, biopolymer flocculant economical and advantageous.     

In vitro antioxidant activity of silymarin

Silymarin, a known standardized extract obtained from seeds of Silybum marianum is widely used in treatment of several diseases of varying origin. In the present paper, we clarified the antioxidant activity of silymarin by employing various in vitro antioxidant assay such as 1,1-diphenyl-2-picryl-hydrazyl free radical (DPPH·) scavenging, 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity, total antioxidant activity determination by ferric thiocyanate, total reducing ability determination by Fe³⁺ ? Fe²⁺ transformation method and Cuprac assay, superoxide anion radical scavenging by riboflavin/methionine/illuminate system, hydrogen peroxide scavenging and ferrous ions (Fe²⁺) chelating activities. Silymarin inhibited 82.7% lipid peroxidation of linoleic acid emulsion at 30 μg/mL concentration; butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), α-tocopherol and trolox indicated inhibition of 83.3, 82.1, 68.1 and 81.3% on peroxidation of linoleic acid emulsion at the same concentration, respectively. In addition, silymarin had an effective DPPH· scavenging, ABTS^√+ scavenging, superoxide anion radical scavenging, hydrogen peroxide scavenging, ferric ions (Fe³⁺) reducing power by Fe³⁺ ? Fe²⁺ transformation, cupric ions (Cu²⁺) reducing ability by Cuprac method, and ferrous ions (Fe²⁺) chelating activities. Also, BHA, BHT, α-tocopherol and trolox, were used as the reference antioxidant and radical scavenger compounds. Moreover, this study, which clarifies antioxidant mechanism of silymarin, brings new information on the antioxidant properties of silymarin. According to the present study, silymarin had effective in vitro antioxidant and radical scavenging activity. It could be used in the pharmacological and food industry because of its antioxidant properties.     

Production and characterization of bioflocculants from bacteria isolated from wastewater treatment plant in South Africa

Bioflocculants produced by six bacteria obtained from activated sludge at a wastewater treatment plant were quantified, purified, and characterized. Effects of pH, temperature, cationic salt content, and specific potential inhibitors on the flocculating activities of the bioflocculants were also determined. Bioflocculants produced by the different bacterial isolates ranged between 6.33 and 27.66 g/L in concentration and were composed of both carbohydrate and protein in varying amounts, as well as a relatively high concentration of uronic acid. The flocculating activity of the broth culture increased during the logarithmic phase of bacterial growth with a maximum ranging from 2.395 to 3.709/OD. Optimum pH for the flocculating activity of the bioflocculants was between 8 and 9, with generally higher flocculating activity observed at 28°C. Of the cations tested, Mg²⁺ and Mn²⁺ improved flocculating activity up to 5.2 fold. The stability of these bacterial bioflocculants under various environmental and nutritional conditions suggests their possible use in the industries and environmental applications. Therefore, this study details important implications in providing a safer alternative flocculation method for wastewater treatment.     

Characterization and flocculating properties of an extracellular biopolymer produced from a Bacillus subtilis DYU1 isolate

Biopolymer DYU500 produced from Bacillus subtilis DYU1 was found to have excellent flocculating ability. With the addition of 40 mg-DYU500/L and 50 mM CaCO₃, the optimum temperature for flocculation performance of DYU500 was 30 °C, giving the highest flocculating activity and rate of 13.5 and 97%, respectively. Analysis with Fourier transform infrared spectrophotometry (FT-IR), nuclear magnetic resonance spectrometry (NMR) and amino acid identification shows that the DYU500 biopolymer mainly possesses the structure of poly-glutamic acid (PGA). The average molecular weight of DYU500 was about (3.16–3.20) × 10⁶ Da as determined by gel permeation chromatography. The major components of biopolymer DYU500 were total sugars, uronic acids, proteins and polyamides (homopolymer of glutamic acid), accounting for a weight ratio of approximate 14.9, 2.7, 4.4 and 48.7% (w/w), respectively. The flocculating activity of DYU500 in the kaolin suspension was markedly stimulated by the addition of bivalent cations Ca²⁺ or Mg²⁺ in optimum concentration ranges of about 0.15–0.90 and 0.10–0.90 mM, respectively. The synergistic effect of cations was most effective at a weak acidic or neutral pH (6.0–7.0). The flocculating activity of DYU500 linearly decreased with an increase in incubation temperature and the activity was completely lost when heating upon 120 °C, arising from the destruction of the polyamides structure of DYU500. Moreover, mechanisms describing the flocculation process with DYU500 were proposed based on the experimental observations.     

Linoleic acid peroxidation initiated by Fe-reducing compounds recovered from Eucalyptus grandis biotreated with Ceriporiopsis subvermispora

This work evaluates linoleic acid peroxidation reactions initiated by Fe³⁺-reducing compounds recovered from Eucalyptus grandis, biotreated with the biopulping fungus Ceriporiopsis subvermispora. The aqueous extracts from biotreated wood had the ability to reduce Fe³⁺ ions from freshly prepared solutions. The compounds responsible for the Fe³⁺-reducing activity corresponded to UV-absorbing substances with apparent molar masses from 3 kDa to 5 kDa. Linoleic acid peroxidation reactions conducted in the presence of Fe³⁺ ions and the Fe³⁺-reducing compounds showed that the rate of O₂ consumption during peroxidation was proportional to the Fe³⁺-reducing activity present in each extract obtained from biotreated wood. This peroxidation reaction was coupled with in-vitro treatment of ball-milled E. grandis wood. Ultraviolet data showed that the reaction system released lignin fragments from the milled wood. Size exclusion chromatography data indicated that the solubilized material contained a minor fraction representing high-molar-mass molecules excluded by the column and a main low-molar-mass peak. Overall evaluation of the data suggested that the Fe³⁺-reducing compounds formed during wood biodegradation by C. subvermispora can mediate lignin degradation through linoleic acid peroxidation.     

Growth of moderately thermophilic iron-oxidizing bacterium strain TI-1 in synthetic medium

The moderately thermophilic iron-oxidizing bacterium strain TI-1, which lacks enzyme systems involved in CO₂ fixation, grows at 45°C in Fe²⁺ medium supplemented with yeast extract to give a maximum cell growth of 1.0 × 10⁸ cells per ml, but does not grow in Fe²⁺ medium without yeast extract. To elucidate the physiology of the strain, a synthetic medium was developed. It was found that the best synthetic medium was Fe²⁺-6AA, containing Fe²⁺, salts, and the following six l-amino acids: alanine, aspartic acid, glutamic acid, arginine, serine, and histidine. In this medium, strain TI-1 showed a maximum cell growth of 10 × 10⁸ cells/ml. The six amino acids in the Fe²⁺-6AA medium were used not only as a carbon source but also as a source of nitrogen. Inorganic nitrogen sources, such as ammonium ion, hydrazine, hydroxylamine, nitrite, and nitrate, were not used as a sole source of nitrogen, but rather strongly inhibited the utilization of the six amino acids at 1 mM. In the Fe²⁺ (10 mM)-6AA medium supplemented with 21 mM Fe³⁺, reduction of Fe³⁺ to Fe²⁺ that was dependent on the added amino acids was observed, suggesting another role of the amino acids in the growth of strain TI-1. Washed, intact cells of strain TI-1 had the activity to reduce Fe³⁺ to Fe²⁺.     

The yeast mitochondrial carrier proteins Mrs3p/Mrs4p mediate iron transport across the inner mitochondrial membrane

The yeast proteins Mrs3p and Mrs4p are two closely related members of the mitochondrial carrier family (MCF), which had previously been implicated in mitochondrial Fe²⁺ homeostasis. A vertebrate Mrs3/4 homologue named mitoferrin was shown to be essential for erythroid iron utilization and proposed to function as an essential mitochondrial iron importer. Indirect reporter assays in isolated yeast mitochondria indicated that the Mrs3/4 proteins are involved in mitochondrial Fe²⁺ utilization or transport under iron-limiting conditions. To have a more direct test for Mrs3/4p mediated iron uptake into mitochondria we studied iron (II) transport across yeast inner mitochondrial membrane vesicles (SMPs) using the iron-sensitive fluorophore PhenGreen SK (PGSK). Wild-type SMPs showed rapid uptake of Fe²⁺ which was driven by the external Fe²⁺ concentration and stimulated by acidic pH. SMPs from the double deletion strain mrs3/4Δ failed to show this rapid Fe²⁺ uptake, while SMPs from cells overproducing Mrs3/4p exhibited increased Fe²⁺ uptake rates. Cu²⁺ was transported at similar rates as Fe²⁺, while other divalent cations, such as Zn²⁺ and Cd²⁺ apparently did not serve as substrates for the Mrs3/4p transporters. We conclude that the carrier proteins Mrs3p and Mrs4p transport Fe²⁺ across the inner mitochondrial membrane. Their activity is dependent on the pH gradient and it is stimulated by iron shortage.     

Study on the flocculability of the Arthrobacter sp., an actinomycete resuscitated from the VBNC state

A bioflocculant with high flocculating activity, LC13-SF, produced by strain LC13^T which was in a viable but nonculturable (VBNC) state, and which was woken up by Rpf (resuscitation promoting factor), was systematically investigated with regard to its fermentation conditions and flocculating activity. The key parameters influencing the bioflocculant LC13-SF were investigated through measuring the optical density at 660 (OD₆₆₀) of the fermentation liquid and the optical density at 550 (OD₅₅₀) of the centrifugal supernatant. The flocculating efficiency and the Zeta potentials were chosen as the response variables for the study of the flocculating activity. The results showed that the optimal conditions for bioflocculant LC13-SF production were a fermentation time of 72 h, an initial pH of 7.0, a fermentation temperature of 30°C and a shaking speed of 150 r/min. The optimized flocculating process was as follows: a final volume percentage of bioflocculant LC13-SF and 0.5% (w/w) CaCl₂ were 1.5 and 5%, respectively in a 4 g/L Kaolin suspension, and the system pH was adjusted to 8.0. Under these conditions, the flocculating efficiency and the absolute value of the Zeta potential reached 94.83% and 4.37, respectively.     

钒钛磁铁尾矿土壤中水黄皮根瘤菌铁耐受性与钝化能力研究

铁是好氧微生物生长所必需的元素,而铁污染土壤环境中的根瘤菌是否对高浓度铁具有耐受性和钝化能力尚不清楚。以攀枝花钒钛磁铁尾矿土壤作为基质进行水黄皮共生根瘤菌捕获实验,获得水黄皮共生根瘤并从中分离纯化出根瘤菌39株。通过Fe~(2+)/Fe~(3+)耐受性和钝化能力测试筛选出耐受性和钝化能力均强的优势菌株PZHS20、PZHS90、PZHS87,其对Fe~(2+)的最大耐受质量浓度为1 600 mg/L,其中PZHS20在200 mg/L Fe~(2+)溶液中钝化效率最大,为73.54%;PZHS90对Fe~(3+)的最大耐受质量浓度为1 600 mg/L,而PZHS20和PZHS87对Fe~(3+)的最大耐受质量浓度为1 800 mg/L,其在200 mg/L Fe~(3+)溶液中钝化效率分别为84.25%和81.95%。16S rRNA基因系统进化分析将PZHS20鉴定为苍白杆菌(Ochrobactrum),将PZHS90和PZHS87鉴定为慢生根瘤菌(Bradyrhizobium)。研究结果表明,钒钛磁铁尾矿土壤中的水黄皮根瘤菌具有不同程度的Fe~(2+)/Fe~(3+)耐受性和钝化能力,筛选出的优势菌株为进一步利用水黄皮-根瘤菌联合修复高浓度铁污染土壤提供可利用的菌株资源。