Characterization of sediment bacteria involved in selenium reduction

Bacterial reduction of selenium (Se) oxyanions (Se[VI] and Se[IV]) to elemental Se (Se[0]) is one of the major biogeochemical processes removing Se from agricultural drainage water and depositing Se in the sediment. This study was conducted to characterize Se-reducing bacterial populations in Lost Hills evaporation pond sediment and to observe their response to Se(VI) and organic C amendments. Se(VI) was removed from the dissolved phase in the sediment slurries amended with organic C with a decrease in redox potential (Eh). Se(VI) concentrations decreased from 2137 to 79 microg L-1 after 9 days of incubation in a 5% soil slurry. Upon our screening process, 9 Se(VI)- and 14 Se(IV)-reducing bacteria were isolated from sediment slurries and identified by amplification and sequencing of 16S rDNA. Bacillus strains appeared to be dominant in the bacterial assemblages active in Se(VI) and Se(IV) reduction in the sediment. Halomonas pacifica and Staphylococcus warneri were also identified as Se(IV)-reducers. Indigenous bacteria have a significant role in the biogeochemical cycling of Se and may be stimulated by addition of a suitable organic source for Se reduction. The bacterial strains isolated from salt-affected and Se-contaminated Lost Hills evaporation pond sediment may have potential application in removing Se from high salt drainage water.     

Biogeochemical regioning problems and the biogeochemical selenium provinces in the former USSR

Current trends in biogeochemical research in the former USSR are exemplified for the trace element selenium (Se). Vast regions of the former USSR are low in Se, giving rise to selenium deficiency diseases in animals and to Kaschin-Beck disease in humans, whereas isolated high-Se regions are comparatively rare. The Se content of plants depends on geological soil-type and secondary processes such as weathering and leaching. In general, a direct correlation between the Se content of feedstock and of the blood in animals is observed, whereas corresponding data for humans remain to be accumulated.     

Trace Element Levels in Scalp Hair of School Children in Shigatse,Tibet, an Endemic Area for Kaschin-Beck Disease (KBD)

Kaschin-Beck disease (KBD) is an endemic osteoarthritis, and the etiology is closely related with levels of trace elements in the human body. Currently, it is clear that the selenium (Se) status of children in KBD areas is lower than that in non-KBD areas in the Tibetan Plateau, whereas role of other elements are yet unknown. This study aimed to assess some essential trace elements (Se, Mo, Mn, Zn, Fe, Cu, Co, and Sr) in children using scalp hair as a biomarker, and 157 samples from school children aged 8–14 years old were collected from both KBD and non-KBD areas in Shigatse, Tibet. Se and Mo were measured by inductive coupled plasma mass spectrometry, and the other elements were determined by inductive coupled plasma optical emission spectrometry. Compared with the non-KBD areas, Se, Mo, Mn, Fe, Zn, Co, and Sr levels of children in KBD areas were found to be significantly different (P < 0.05); while in linear discriminant analysis, only Se and Zn were found to contribute to the KBD prevalence in the study area. The hair Se level of children in KBD areas ranged from 0.115 to 0.299 mg/kg, while in non-KBD areas it ranged from 0.135 to 0.519 mg/kg. The Zn content of children’s hair was between 83 and 207 mg/kg in KBD areas, while it was 37 and 219 mg/kg in non-KBD areas. Lower Se and higher Zn levels in children in KBD areas was found when compared with non-KBD groups. In addition, Mo levels were found to be different between KBD areas and non-KBD areas on the opposite side of the Yarlung Zangbo River, but no close relationship was shown because there was no difference compared with the non-KBD area on the same side of the river. Our observations suggest that Se deficiency is still an important factor for the occurrence and prevalence of KBD, while the relationship between Zn and KBD needs to be further explored in the Tibetan Plateau.     

Evaluation of selenite bioremoval from liquid culture by Enterococcus species

The genus Enterococcus belong to the genera of bacteria that produce lactic acid and can confer health benefits to living organisms. Selenium (Se) is an essential micronutrient for humans and animals. Thirty-six Enterococcus species isolated from dairy products were screened for Se(IV) sorption capacity for use as a probiotics in animal nutrition. Several isolates grew luxuriantly and significantly removed Se(IV) from Se(IV) amended medium. Two isolates, LAB 14 and LAB 18, identified by 16S rRNA gene sequence analysis as Enterococcus faecalis (98% nucleotide sequence similarity) and Enterococcus faecium (97% nucleotide sequence similarity), respectively, were selected for further studies. The two isolates grew optimally and removed selenium at initial pH 7.0. Optimum removal of Se(IV) from the medium was recorded at 25 °C. Time course studies showed that after 8 h of incubation LAB 14 and LAB 18 cultures displayed the highest biomass production and Se(IV) bioremoval and most selenite in culture depleted in 24 h. At initial concentrations of 10 mg L⁻¹ and 60 mg L⁻¹, E. faecium (LAB 18) removed 9.91 mg L⁻¹ and 59.70 mg L⁻¹, respectively after 24 h. Similar Se(IV) bioremoval capacity was recorded with E. faecalis (LAB 14). Substantial amount of Se was detected in biomass of E. faecium (0.4599 mg g⁻¹ of dry weight) and E. faecalis (0.4759 mg g⁻¹ of dry weight). The significant uptake and transformation of Se(IV) by the Enterococcus species observed in this study suggest that they can be used to deliver dietary Se through feed augmentation with Se(IV)-enriched Enterococcus biomass.     

Bioeffects of selenite on the growth of Spirulina platensis and its biotransformation

The bioeffects of selenium on the growth of Spirulina platensis and the selenium distribution were investigated. S. platensis was batch cultured in Zarrouk medium containing increasing concentrations of sodium selenite. The biotransformation characteristic of selenium was analysed by the determination of the detailed selenium distribution forms. At 35 degrees C, 315.2 microEm(-2) x s(-1), sodium selenite concentrations below 400 mg x l(-1) were found to stimulate algal growth, especially in the range of 0.5-40 mg x l(-1). However, above 500 mg x l(-1) sodium selenite was toxic to this alga with the toxicity being related to the sulfite level in the medium. S. platensis was found to resist higher selenite by reducing toxic Se(IV) to nonsoluble Se(0). Selenium was accumulated efficiently in S. platensis during cultivation with accumulated selenium increasing with selenite concentration in the medium. It was demonstrated that inorganic selenite could be transformed into organic forms through binding with protein, lipids and polysaccharides and other cell components. The organic selenium accounted for 85.1% of the total accumulated selenium and was comprised of 25.2% water-soluble protein-bound, 10.6% lipids-bound and 2.1% polysaccharides-bound selenium. Among the organic fractions lipid possessed the strongest ability to accumulate Se (6.47 mg x kg(-1)). The 14.9% inorganic selenium in S. platensis was composed of Se(IV) (13.7%) and Se(VI) (1.2%).     

X-ray absorption spectroscopy study shows that the rapid selenium volatilizer, pickleweed (Salicornia bigelovii Torr.), reduces selenate to organic forms without the aid of microbes

In many plant species, selenium (Se) volatilization is limited by the reduction of selenate and its chemical conversion to organic Se compounds, a process that may be facilitated by rhizosphere microbes. This study was conducted to determine if pickleweed (Salicornia bigelovii Torr.), which is characterized by having high rates of Se volatilization from selenate, is able to reduce selenate into organic forms of Se axenically, or whether it requires the presence of microbes. X-ray absorption spectroscopy analysis showed that shoots and roots of pickleweed plants supplied with 50 microM selenate accumulated Se predominantly in organic Se forms (about 65-75% of the total accumulated Se), regardless of whether the plants were grown axenically or in the presence of microbes. The results suggest that, unlike other species for which selenate reduction appears to be rate limiting. e.g. Indian mustard (Brassica juncea L.) and broccoli (Brassica oleracea L.), pickleweed is unusual in that it has an enhanced capacity to reduce selenate to organic forms that is independent of the presence of rhizosphere microbes.     

定向驯化对异养蛋白核小球藻硒的耐受性及富集能力的影响

硒(Se)是生物体必不可少的微量元素,硒缺乏会导致人产生克山病、大骨节病等疾病,缺硒也会给畜牧业带来巨大损失。目前的补硒产品存在硒含量和生物利用度低、安全性差等问题,而通过小球藻培养可获得生物利用度高、安全性好的有机硒,因此是非常有应用前景的补硒产品。首先,为了获得对硒的耐受性和富集能力更强的藻种,研究通过定向驯化的方式逐步提高培养基中Na₂SeO₃浓度来驯化蛋白核小球藻,并对驯化时间和驯化过程中Na₂SeO₃的浓度梯度进行了优化。结果表明,驯化后的藻种对硒的耐受性和富集能力明显提高。在5L发酵罐中,驯化后的藻株可以耐受40mg/L的Na₂SeO₃,胞内有机硒合成速率提高了175.6%。之后,在5L发酵罐中进一步优化了硒的补加方式,在异养培养过程中分批补料添加40mg/LNa₂SeO₃时,最终获得的蛋白核小球藻细胞干重达106.4g/L,有机硒含量为1227mg/kg,有机硒合成速率为1.36mg/(L·h)。研究结果与已有蛋白核小球藻异养富硒文献报道的最高细胞密度75g/L和最高有机硒含量560mg/kg相比分别提高了41.9%和119.1%。上述结果表明,通过定向驯化的方法,可大大提高蛋白核小球藻对硒的耐受性和富集能力。     

Production of Selenium-Enriched Biomass by Enterococcus durans

Selenium (Se) is an essential micronutrient for several organisms, and there is an increased interest about adequate sources for dietary selenium supplementation. The aim of this study was to evaluate the selenium bioaccumulation capacity of an Enterococcus strain. The isolate LAB18s was identified as Enterococcus durans by the VITEK® 2 system and analysis of both 16S rDNA gene sequence (JX503528) and the 16S-23S rDNA intergenic spacer (ITS). After 24-h incubation, E. durans LAB18s bioaccumulated elevated Se(IV) concentrations, reaching 2.60 and 176.97 mg/g in media containing initial amounts of 15 and 240 mg/l sodium selenite, respectively. The isolate grew optimally and had high selenium bioaccumulation at initial pH of 7.0 and 30 °C. Time course studies showed that E. durans LAB18s displayed the highest bioaccumulation of Se(IV) after 6 h of incubation. Analyses from scanning electron microscopy (SEM) demonstrated the presence of filaments connecting the cells of E. durans LAB18s cultivated in the presence of sodium selenite. It was demonstrated that a considerable amount of Se(IV) was absorbed by E. durans LAB18s. Therefore, this strain may represent an alternative source of organic dietary selenium.     

Proteomic characterization of a selenium-metabolizing probiotic Lactobacillus reuteri Lb2 BM for nutraceutical applications

Selenium (Se), Se‐cysteines and selenoproteins have received growing interest in the nutritional field as redox‐balance modulating agents. The aim of this study was to establish the Se‐concentrating and Se‐metabolizing capabilities of the probiotic Lactobacillus reuteri Lb2 BM, for nutraceutical applications. A comparative proteomic approach was employed to study the bacteria grown in a control condition (MRS modified medium) and in a stimulated condition (4.38 mg/L of sodium selenite). The total protein extract was separated into two pI ranges: 4–7 and 6–11; the 25 identified proteins were divided into five functional classes: (i) Se metabolism; (ii) energy metabolism; (iii) stress/adhesion; (iv) cell shape and transport; (v) proteins involved in other functions. All the experimental results indicate that L. reuteri Lb2 BM is able to metabolize Se(IV), incorporating it into selenoproteins, through the action of a selenocysteine lyase, thus enhancing organic Se bioavailability. This involves endo‐ergonic reactions balanced by an increase of substrate‐level phosphorylation, chiefly through lactic fermentation. Nevertheless, when L. reuteri was grown on Se a certain degree of stress was observed, and this has to be taken into account for future applicative purposes. The proteomic approach has proven to be a powerful tool for the metabolic characterization of potential Se‐concentrating probiotics.     

Opposite effect of Cu(II) and Se(IV) ions on the antibacterial-toxic action of mycotoxins

The effect of Se(IV) and Cu(II) ions on the antibacterial activity of aflatoxins and ochratoxin A (mycotoxins) was studied in BioArena as a complex bioautographic system. In the presence of 0.23 and 0.46 mg/100 mL Se(IV) the inhibition zones of mycotoxins were decreased, however, lower concentration (0.046 mg/100 mL) increased the antibacterial effect of aflatoxin B1. Cu(II) (1.53 mg/100 mL) enhanced the toxicity of mycotoxins. The results supported the possible role of formaldehyde and its reaction products (e.g. 1O2, O3) in the antibacterial-toxic action of mycotoxins. Cu(II) can probably generate and mobilise the formaldehyde molecules and so it could increase the toxicity with its potential reaction products. It is possible that the enzymatic or spontaneous methylation of Se(IV) takes place through formaldehyde, which may cause partial formaldehyde depletion in the system. The enhanced antibacterial effect at low concentration Se(IV) is overlapping with the often experienced prooxidant effect in cases of natural antioxidants.     

Selenite Enhances Immune Response against Pseudomonas aeruginosa PA14 via SKN-1 in Caenorhabditis elegans

Background

Selenium (Se) is an important nutrient that carries out many biological processes including maintaining optimal immune function. Here, inorganic selenite (Se(IV)) was evaluated for its pathogen resistance and potential-associated factors in Caenorhabditis elegans. The immune effects of Se(IV) were investigated by examining the responses of C. elegans to Pseudomonas aerugonisa PA14 strain.

Principal Findings

Se(IV)-treated C. elegans showed increased survival under PA14 infection compared with untreated controls. The significant pathogen resistance of Se(IV) on C. elegans might not be attributed to the effects of Se(IV) on PA14 as Se(IV) showed no effect on bacterial quorum-sensing and virulence factors of PA14. This study showed that Se(IV) enhanced the expression of a gene pivotal for the innate immunity in C. elegans. The study found that the pathogen-resistant phenotypes contributed by Se(IV) was absent from the skn-1 mutant worms. Moreover, Se(IV) influenced the subcellular distribution of SKN-1/Nrf in C. elegans upon PA14 infection. Furthermore, Se(IV) increased mRNA levels of SKN-1 target genes (gst-4 and gcs-1).

Conclusions

This study found evidence of Se(IV) protecting C. elegans against P. aeruginosa PA14 infection by exerting effects on the innate immunity of C. elegans that is likely mediated via regulation of a SKN-1-dependent signaling pathway.     

Se和V_E与克山病

以克山病病区粮配成基础饲料,另在基础饲料中分别补充Ｓｅ或ＶＥ,或Ｓｅ＋ＶＥ喂养大鼠,在细胞及亚细胞水平上以Ｃａ代谢为主研究并比较了Ｓｅ和ＶＥ在克山病病因中的作用。测量了心肌细胞和心肌线粒体的Ｃａ代谢及有关指标、心肌线粒体能量转换功能及心肌组织自由基含量。结果表明,在低Ｓｅ病区粮中补充Ｓｅ或ＶＥ均能在一定程度上预防病区粮中致病因素对心肌细胞及线粒体的损伤;并且补充Ｓｅ或ＶＥ均能使心肌组织中自由基含量减少。提示Ｓｅ和ＶＥ是通过清除体内过量自由基预防细胞和线粒体的损伤的。但值得注意的是,实验中所用病区粮ＶＥ含量不低于甚至高于非病区对照粮,在低Ｓｅ情况下,所补ＶＥ的量需要相当大（如本实验中补充２００μｇ／ｇ）才能较明显地预防心肌细胞和心肌线粒体的损伤。通过对这些结果的分析,进一步肯定低Ｓｅ是克山病形成的重要因素之一。     

Selenite removal and reduction by growing <Emphasis Type="Italic">Aspergillus</Emphasis> sp. J2

In this study, the removal and reduction of selenite [Se(IV)] by growing Aspergillus sp. J2 were investigated. The lag phase, growth rate and biomass of J2 was not significantly influenced by the presence of 100 mg/L Se(IV). A rapid Se(IV) removal process took place from the 3rd to the 4th day during the growth of J2. Scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction analyses showed that the Se(IV) did not cause any visible effects on cell morphology and the reduced amorphous elemental selenium [Se(0)] nanoparticles were mainly on the surface of the mycelial cell walls. The macromolecules containing amine groups also interact with Se(IV) and could play an important role in Se(IV) removal by J2.     

Selenium (IV,VI) reduction and tolerance by fungi in an oxic environment

Microbial processes are known to mediate selenium (Se) oxidation–reduction reactions, strongly influencing Se speciation, bioavailability, and transport throughout the environment. While these processes have commonly been studied in anaerobic bacteria, the role that aerobic fungi play in Se redox reactions could be important for Se‐rich soil systems, dominated by microbial activity. We quantified fungal growth, aerobic Se(IV, VI) reduction, and Se immobilization and volatilization in the presence of six, metal‐tolerant Ascomycete fungi. We found that the removal of dissolved Se was dependent on the fungal species, Se form (i.e., selenite or selenate), and Se concentration. All six species grew and removed dissolved Se(IV) or Se(VI) from solution, with five species reducing both oxyanions to Se(0) biominerals, and all six species removing at least 15%–20% of the supplied Se via volatilization. Growth rates of all fungi, however, decreased with increasing Se(IV,VI) concentrations. All fungi removed 85%–93% of the dissolved Se(IV) within 10 d in the presence of 0.01 mm Se(IV), although only about 20%–30% Se(VI) was removed when grown with 0.01 mm Se(VI). Fungi‐produced biominerals were typically 50‐ to 300‐nm‐diameter amorphous or paracrystalline spherical Se(0) nanoparticles. Our results demonstrate that activity of common soil fungi can influence Se form and distribution, and these organisms may therefore play a role in detoxifying Se‐polluted environments.     

Bacterial reduction of selenate to elemental selenium utilizing molasses as a carbon source

Selecting an inexpensive and effective organic carbon source is the key to reducing the cost in selenium (Se) remediation. Five bacteria were screened based on their ability in using molasses as an organic carbon source to reduce selenate [Se(VI)] in drainage water. Efficiency of Se removal differed in the molasses-added drainage water containing different bacteria, with an order of Enterobacter taylorae>Pantoea sp. SSS2>Klebsiella sp. WRS2>Citerobacter freundii>Shigella sp. DW2. By using E. taylorae, 97% of the added Se(VI) (1000 microg/L) was reduced to elemental Se [Se(0)] in an artificial drainage water during an 11-day experiment, and 93% of Se(VI) in a natural agricultural drainage water was reduced to Se(0) and organic Se during a 7-day experiment. E. taylorae also rapidly removed Se(VI) in agar-coated sand columns. During 45 days of the experiment, more than 92% of influent Se was removed from the drainage water with a molasses range of 0.01-0.1%. This study reveals that molasses may be a cost-effective organic carbon source used by Se(VI)-reducing bacteria to remove Se from agricultural drainage water in field.     

Effect of Organic Selenium Supplementation on Growth, Se Uptake, and Nutrient Utilization in Guinea Pigs

Forty weaned male guinea pigs (Cavia porcellus) of 152.6?±?7.96 g mean body weight were divided into four equal groups and fed a common basal diet comprised of 25% ground cowpea (Vigna unguiculata) hay, 30% ground maize (Zea mays) grain, 22% ground gram (Cicer arietinum) grain, 9.5% deoiled rice (Oryza sativa) bran, 6% soybean (Glycine max) meal, 6% fish meal, 1.5% mineral mixture (without Se), and ascorbic acid at 200 mg/kg to meet their nutrient requirements along with 0, 0.1, 0.2, and 0.3 ppm of organic selenium (Se) in groups I, II, III, and IV, respectively. Experimental feeding lasted for a period of 10 weeks, during which, daily feed intake and weekly body weights were recorded. Intake and digestibility of dry matter, organic matter, ether extract, crude fiber, and nitrogen-free extract as well as uptake of calcium and phosphorus were similar (P?>?0.05) among the four groups. Feed:gain ratio was also similar (P?>?0.05) in the four groups. However, digestibility of crude protein was significantly (P?<?0.001) higher in group II supplemented with 0.1 ppm organic Se as compared to other three group. Intake and absorption of Se was significantly (P?<?0.001) higher in all the Se supplemented groups as compared to control group. Average daily gain (ADG) was significantly (P?<?0.05) higher in group II (3.16 g/day) and III (3.38 g/day) as compared to group I (2.88 g/day). However, ADG in group IV (supplemented 0.3 ppm organic Se) was significantly (P?<?0.05) lower (2.83 g/day) than group II and III, but comparable (P?>?0.05) to group I. Findings of the present experiment suggests that Se requirements of guinea pigs are ≥0.2 ppm, as supplementation of 0.1 ppm organic Se in the diet (having 0.1 ppm Se) not only enhanced their growth rate but also improved the protein utilization.     

The Endogenous Nitric Oxide Mediates Selenium-Induced Phytotoxicity by Promoting ROS Generation in Brassica rapa

Selenium (Se) is suggested as an emerging pollutant in agricultural environment because of the increasing anthropogenic release of Se, which in turn results in phytotoxicity. The most common consequence of Se-induced toxicity in plants is oxidative injury, but how Se induces reactive oxygen species (ROS) burst remains unclear. In this work, histofluorescent staining was applied to monitor the dynamics of ROS and nitric oxide (NO) in the root of Brassica rapa under Se(IV) stress. Se(IV)-induced faster accumulation of NO than ROS. Both NO and ROS accumulation were positively correlated with Se(IV)-induced inhibition of root growth. The NO accumulation was nitrate reductase (NR)- and nitric oxide synthase (NOS)-dependent while ROS accumulation was NADPH oxidase-dependent. The removal of NO by NR inhibitor, NOS inhibitor, and NO scavenger could alleviate Se(IV)-induced expression of Br_Rbohs coding for NADPH oxidase and the following ROS accumulation in roots, which further resulted in the amelioration of Se(IV)-induced oxidative injury and growth inhibition. Thus, we proposed that the endogenous NO played a toxic role in B. rapa under Se(IV) stress by triggering ROS burst. Such findings can be used to evaluate the toxic effects of Se contamination on crop plants.     

Quinone-mediated reduction of selenite and tellurite by Escherichia coli

The reduction of selenite (Se(IV)) and tellurite (Te(IV)) by Escherichia coli was significantly enhanced by various quinone redox mediators (lawsone, menadione, anthraquinone-2-sulfonate, and anthraquinone-2,6-disulfonate). In the presence of 0.2mM lawsone, over 99.1% Se(IV) and around 96.4% Te(IV) were reduced in 8 h, at average reduction rates of 9.1 and 7.6 mM g cell(-1) h(-1), respectively. Better mediated reduction of Se(IV) and Te(IV) were observed when lawsone concentration increased from 0.1 to 0.4 mM and cell concentration increased from 0.1 to 0.6 g l(-1), respectively. Transmission electron microscopy analysis revealed the formation of both intracellular and extracellular Se(0) nanospheres or Te(0) nanorods, and the presence of lawsone increased the formation and accumulation of extracellular precipitates. The efficient mediated microbial reduction of Se(IV)/Te(IV) may be exploited for pollution removal and biological nanomaterials production.     

Aerobic microbial manufacture of nanoscale selenium: exploiting nature’s bio-nanomineralization potential

The potential of the environment to yield organisms that can produce functional bionanominerals is demonstrated by selenium-tolerant, aerobic bacteria isolated from a seleniferous rhizosphere soil. An isolate, NS3, was identified as a Bacillus species (EU573774.1) based on morphological and 16S rRNA characterization. This strain reduced Se(IV) under aerobic conditions to produce amorphous α Se(0) nanospheres. A room-temperature washing treatment was then employed to remove the biomass and resulted in the production of clusters of hexagonal Se(0) nano-rods. The Se(0) nanominerals were analyzed using electron microscopy and X-ray diffraction techniques. This Bacillus isolate has the potential to be used both in the neutralizing of toxic Se(IV) anions in the environment and in the environmentally friendly manufacture of nanomaterials.     

Design and application of a rapid screening technique for isolation of selenite reduction-deficient mutants of Shewanella putrefaciens

A rapid screening technique for isolation of selenite (Se(IV)) reduction-deficient (Ser) mutants was developed and used to identify four Ser mutants of Shewanella putrefaciens. Two Ser mutants were unable to grow anaerobically on fumarate, nitrate or nitrite. Two other Ser mutants were unable to grow anaerobically on all compounds tested as sole terminal electron acceptor. Previously isolated Mn(IV) reduction-deficient mutants displayed Ser-positive phenotypes and reduced Se(IV) at wild-type rates, while two of nine Fe(III) reduction-deficient mutants displayed Ser-negative phenotypes and reduced Se(IV) at low rates. This study provides the first reported method for isolation of Ser mutants and demonstrates that Se(IV) reduction by S. putrefaciens is respiratory chain-linked.