Correlative Cryogenic Spectromicroscopy to Investigate Selenium Bioreduction Products

Fakra, Sirine C.; Luef, Birgit; Castelle, Cindy J.; Mullin, Sean W.; Williams, Kenneth H.; Marcus, Matthew A.; Schichnes, Denise; Banfield, Jillian F.

doi:10.1021/acs.est.5b01409

Cited by 25 publications

(24 citation statements)

References 95 publications

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“…All spectra recorded in the range 12500–13070eV, were deadtime-corrected, deglitched, calibrated, pre-edge background substracted, and post-edge normalized using a suite of custom LabVIEW software available at the beamline. Least-squares linear combination fitting (LCF) of experimental XANES spectra was performed in the range of 12630 to 12850 eV using a library of 52 standard selenocompounds (Fakra et al, 2018 ). The best LCF was obtained by minimizing the normalized sum of squares residuals (NSS = 0 = perfect fit).…”

Section: Methodsmentioning

confidence: 99%

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Characterization of Selenium Accumulation, Localization and Speciation in Buckwheat–Implications for Biofortification

et al. 2018

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Buckwheat is an important crop species in areas of selenium (Se) deficiency. To obtain better insight into their Se metabolic properties, common buckwheat (Fagopyrum esculentum) and tartary buckwheat (F. tataricum) were supplied with different concentrations of Se, supplied as selenate, selenite, or Astragalus bisulcatus plant extract (methyl-selenocysteine). Se was supplied at different developmental stages, with different durations, and in the presence or absence of potentially competing ions, sulfate, and phosphate. The plants were analyzed for growth, Se uptake, translocation, accumulation, as well as for Se localization and chemical speciation in the seed. Plants of both buckwheat species were supplied with 20 μM of either of the three forms of Se twice over their growth period. Both species accumulated 15–40 mg Se kg−1 DW in seeds, leaves and stems, from all three selenocompounds. X-ray microprobe analysis showed that the Se in seeds was localized in the embryo, in organic C-Se-C form(s) resembling selenomethionine, methyl-selenocysteine, and γ-glutamyl-methylselenocysteine standards. In short-term (2 and 24 h) Se uptake studies, both buckwheat species showed higher Se uptake rate and shoot Se accumulation when supplied with plant extract (methyl-selenocysteine), compared to selenite or selenate. In long-term (7 days) uptake studies, both species were resistant to selenite up to 50 μM. Tartary buckwheat was also resistant to selenate up to 75 μM Se, but >30 μM selenate inhibited common buckwheat growth. Selenium accumulation was similar in both species. When selenite was supplied, Se levels were 10–20-fold higher in root (up to 900 mg Se kg−1 DW) than shoot, but 4-fold higher in shoot (up to 1,200 mg Se kg−1 DW) than root for selenate-supplied plants. Additionally, sulfate and phosphate supply affected Se uptake, and conversely selenate enhanced S and P accumulation in both species. These findings have relevance for crop Se biofortification applications.

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Section: Methodsmentioning

confidence: 99%

“…The error margin for the fraction found for selenocompounds is ±10%. Additionally, valence-state scatter plots, where each datapoint represent a XANES spectrum, were obtained for quick visualization of Se valence state in the samples, following procedures detailed in Fakra et al ( 2018 ).…”

Section: Methodsmentioning

confidence: 99%

Characterization of Selenium Accumulation, Localization and Speciation in Buckwheat–Implications for Biofortification

et al. 2018

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“…Because it has low solubility, biogenic Se(0) production is often considered a beneficial bioremediation strategy for limiting Se mobility in the environment and reducing its ability to enter the food chain. However, biogenic Se(0) tends to be nanoparticulate, with most organisms forming amorphous spherical particles with 100-300 nm diameters (Fakra et al, 2015;Oremland et al, 2004).…”

Section: Se(iv) Mediamentioning

confidence: 99%

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

et al. 2017

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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.

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“…Least square linear combination (LSQ) fitting of Se XANES spectra was performed in the 12630–12850 eV range, using a library of standard seleno-compounds. As Se standards a library of 52 compounds was used ( Fakra et al, 2018 ). All data processing and analyses were performed with a suite of custom LabVIEW (National Instruments, Austin, TX, United States) programs available at the beamline.…”

Section: Methodsmentioning

confidence: 99%

Fungal Endophyte Alternaria tenuissima Can Affect Growth and Selenium Accumulation in Its Hyperaccumulator Host Astragalus bisulcatus

et al. 2018

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Endophytes can enhance plant stress tolerance by promoting growth and affecting elemental accumulation, which may be useful in phytoremediation. In earlier studies, up to 35% elemental selenium (Se0) was found in Se hyperaccumulator Astragalus bisulcatus. Since Se0 can be produced by microbes, the plant Se0 was hypothesized to be microbe-derived. Here we characterize a fungal endophyte of A. bisulcatus named A2. It is common in seeds from natural seleniferous habitat containing 1,000–10,000 mg kg-1 Se. We identified A2 as Alternaria tenuissima via 18S rRNA sequence analysis and morphological characterization. X-ray microprobe analysis of A. bisulcatus seeds that did or did not harbor Alternaria, showed that both contained >90% organic seleno-compounds with C-Se-C configuration, likely methylselenocysteine and glutamyl-methylselenocysteine. The seed Se was concentrated in the embryo, not the seed coat. X-ray microprobe analysis of A2 in pure culture showed the fungus produced Se0 when supplied with selenite, but accumulated mainly organic C-Se-C compounds when supplied with selenate. A2 was completely resistant to selenate up to 300 mg L-1, moderately resistant to selenite (50% inhibition at ∼50 mg Se L-1), but relatively sensitive to methylselenocysteine and to Se extracted from A. bisulcatus (50% inhibition at 25 mg Se L-1). Four-week old A. bisulcatus seedlings derived from surface-sterilized seeds containing endophytic Alternaria were up to threefold larger than seeds obtained from seeds not showing evidence of fungal colonization. When supplied with Se, the Alternaria-colonized seedlings had lower shoot Se and sulfur levels than seedlings from uncolonized seeds. In conclusion, A. tenuissima may contribute to the Se0 observed earlier in A. bisulcatus, and affect host growth and Se accumulation. A2 is sensitive to the Se levels found in its host’s tissues, but may avoid Se toxicity by occupying low-Se areas (seed coat, apoplast) and converting plant Se to non-toxic Se0. These findings illustrate the potential for hyperaccumulator endophytes to affect plant properties relevant for phytoremediation. Facultative endophytes may also be applicable in bioremediation and biofortification, owing to their capacity to turn toxic inorganic forms of Se into non-toxic or even beneficial, organic forms with anticarcinogenic properties.

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Correlative Cryogenic Spectromicroscopy to Investigate Selenium Bioreduction Products

Cited by 25 publications

References 95 publications

Characterization of Selenium Accumulation, Localization and Speciation in Buckwheat–Implications for Biofortification

Characterization of Selenium Accumulation, Localization and Speciation in Buckwheat–Implications for Biofortification

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

Fungal Endophyte Alternaria tenuissima Can Affect Growth and Selenium Accumulation in Its Hyperaccumulator Host Astragalus bisulcatus

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