Dataset Information

Reduction of selenite to Se(0) nanoparticles by filamentous bacterium Streptomyces sp. ES2-5 isolated from a selenium mining soil.

ABSTRACT: BACKGROUND:Selenium (Se) is an essential trace element in living systems. Microorganisms play a pivotal role in the selenium cycle both in life and in environment. Different bacterial strains are able to reduce Se(IV) (selenite) and (or) Se(VI) (selenate) to less toxic Se(0) with the formation of Se nanoparticles (SeNPs). The biogenic SeNPs have exhibited promising application prospects in medicine, biosensors and environmental remediation. These microorganisms might be explored as potential biofactories for synthesis of metal(loid) nanoparticles. RESULTS:A strictly aerobic, branched actinomycete strain, ES2-5, was isolated from a selenium mining soil in southwest China, identified as Streptomyces sp. based on 16S rRNA gene sequence, physiologic and morphologic characteristics. Both SEM and TEM-EDX analysis showed that Se(IV) was reduced to Se(0) with the formation of SeNPs as a linear chain in the cytoplasm. The sizes of the SeNPs were in the range of 50-500 nm. The cellular concentration of glutathione per biomass decreased along with Se(IV) reduction, and no SeNPs were observed in different sub-cellular fractions in presence of NADPH or NADH as an electron donor, indicating glutathione is most possibly involved in vivo Se(IV) reduction. Strain ES2-5 was resistant to some heavy metal(loid)s such as Se(IV), Cr(VI) and Zn(II) with minimal inhibitory concentration of 50, 80 and 1.5 mM, respectively. CONCLUSIONS:The reducing mechanism of Se(IV) to elemental SeNPs under aerobic condition was investigated in a filamentous strain of Streptomyces. Se(IV) reduction is mediated by glutathione and then SeNPs synthesis happens inside of the cells. The SeNPs are released via hypha lysis or fragmentation. It would be very useful in Se bioremediation if Streptomyces sp. ES2-5 is applied to the contaminated site because of its ability of spore reproduction, Se(IV) reduction, and adaptation in soil.

SUBMITTER: Tan Y

PROVIDER: S-EPMC5024524 | biostudies-literature | 2016 Sep

REPOSITORIES: biostudies-literature

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Reduction of selenite to Se(0) nanoparticles by filamentous bacterium Streptomyces sp. ES2-5 isolated from a selenium mining soil.

Tan Yuanqing Y Yao Rong R Wang Rui R Wang Dan D Wang Gejiao G Zheng Shixue S

Microbial cell factories 20160915 1

<h4>Background</h4>Selenium (Se) is an essential trace element in living systems. Microorganisms play a pivotal role in the selenium cycle both in life and in environment. Different bacterial strains are able to reduce Se(IV) (selenite) and (or) Se(VI) (selenate) to less toxic Se(0) with the formation of Se nanoparticles (SeNPs). The biogenic SeNPs have exhibited promising application prospects in medicine, biosensors and environmental remediation. These microorganisms might be explored as poten ...[more]

PMID: 27630128

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Project description:4-Coumarate:coenzyme A ligase (4CL) plays a key role in phenylpropanoid metabolism, providing precursors for a large variety of important plant secondary metabolites, such as lignin, flavonoids, and phytoalexins. Although 4CLs have been believed to be specific to plants, a gene encoding a 4CL-like enzyme which shows more than 40% identity in amino acid sequence to plant 4CLs was found in the genome of the gram-positive, filamentous bacterium Streptomyces coelicolor A3(2). The recombinant enzyme, produced in Escherichia coli with a histidine tag at its N-terminal end, showed distinct 4CL activity. The optimum pH and temperature of the reaction were pH 8.0 and 30 degrees C, respectively. The K(m) value for 4-coumarate and k(cat) were determined as 131 +/- 4 micro M and 0.202 +/- 0.007 s(-1), respectively. The K(m) value was comparable to those of plant 4CLs. The substrate specificity of this enzyme was, however, distinctly different from those of plant 4CLs. The enzyme efficiently converted cinnamate (K(m), 190 +/- 2 micro M; k(cat), 0.475 +/- 0.012 s(-1)), which is a very poor substrate for plant 4CLs. Furthermore, the enzyme showed only low activity toward caffeate and no activity toward ferulate, both of which are generally good substrates for plant 4CLs. The enzyme was therefore named ScCCL for S. coelicolor A3(2) cinnamate CoA ligase. To determine the amino acid residues providing the unique substrate specificity of ScCCL, eight ScCCL mutant enzymes having a mutation(s) at amino acid residues that probably line up along the substrate-binding pocket were generated. Mutant A294G used caffeate as a substrate more efficiently than ScCCL, and mutant A294G/A318G used ferulate, which ScCCL could not use as a substrate, suggesting that Ala(294) and Ala(318) are involved in substrate recognition. Furthermore, the catalytic activities of A294G and A294G/A318G toward cinnamate and 4-coumarate were greatly enhanced compared with those of the wild-type enzyme.

Project description:A wide range of microorganisms have been shown to transform selenium-containing oxyanions to reduced forms of the element, particularly selenium-containing nanoparticles. Such reactions are promising for the detoxification of environmental contamination and the production of valuable selenium-containing products, such as nanoparticles for application in biotechnology. It has previously been shown that aerobic methane-oxidizing bacteria, including Methylococcus capsulatus (Bath), are able to perform the methane-driven conversion of selenite (SeO32-) to selenium-containing nanoparticles and methylated selenium species. Here, the biotransformation of selenite by Mc. capsulatus (Bath) has been studied in detail via a range of imaging, chromatographic, and spectroscopic techniques. The results indicate that the nanoparticles are produced extracellularly and have a composition distinct from that of nanoparticles previously observed from other organisms. The spectroscopic data from the methanotroph-derived nanoparticles are best accounted for by a bulk structure composed primarily of octameric rings in the form Se8 -x S x with an outer coat of cell-derived biomacromolecules. Among a range of volatile methylated selenium and selenium-sulfur species detected, methyl selenol (CH3SeH) was found only when selenite was the starting material, although selenium nanoparticles (both biogenic and chemically produced) could be transformed into other methylated selenium species. This result is consistent with methyl selenol being an intermediate in the methanotroph-mediated biotransformation of selenium to all the methylated and particulate products observed.IMPORTANCE Aerobic methane-oxidizing bacteria are ubiquitous in the environment. Two well-characterized strains, Mc. capsulatus (Bath) and Methylosinus trichosporium OB3b, representing gamma- and alphaproteobacterial methanotrophs, respectively, can convert selenite, an environmental pollutant, to volatile selenium compounds and selenium-containing particulates. Both conversions can be harnessed for the bioremediation of selenium pollution using biological or fossil methane as the feedstock, and these organisms could be used to produce selenium-containing particles for food and biotechnological applications. Using an extensive suite of techniques, we identified precursors of selenium nanoparticle formation and also found that these nanoparticles are made up of eight-membered mixed selenium and sulfur rings.

Project description:Bacillus mycoides SeITE01 is an environmental isolate that transforms the oxyanion selenite ( SeO32- ) into the less bioavailable elemental selenium (Se0) forming biogenic selenium nanoparticles (Bio-SeNPs). In the present study, the reduction of sodium selenite (Na2SeO3) by SeITE01 strain and the effect of SeO32- exposure on the bacterial cells was examined through untargeted metabolomics. A time-course approach was used to monitor both cell pellet and cell free spent medium (referred as intracellular and extracellular, respectively) metabolites in SeITE01 cells treated or not with SeO32- . The results show substantial biochemical changes in SeITE01 cells when exposed to SeO32- . The initial uptake of SeO32- by SeITE01 cells (3h after inoculation) shows both an increase in intracellular levels of 4-hydroxybenzoate and indole-3-acetic acid, and an extracellular accumulation of guanosine, which are metabolites involved in general stress response adapting strategies. Proactive and defensive mechanisms against SeO32- are observed between the end of lag (12h) and beginning of exponential (18h) phases. Glutathione and N-acetyl-L-cysteine are thiol compounds that would be mainly involved in Painter-type reaction for the reduction and detoxification of SeO32- to Se0. In these growth stages, thiol metabolites perform a dual role, both acting against the toxic and harmful presence of the oxyanion and as substrate or reducing sources to scavenge ROS production. Moreover, detection of the amino acids L-threonine and ornithine suggests changes in membrane lipids. Starting from stationary phase (24 and 48h), metabolites related to the formation and release of SeNPs in the extracellular environment begin to be observed. 5-hydroxyindole acetate, D-[+]-glucosamine, 4-methyl-2-oxo pentanoic acid, and ethanolamine phosphate may represent signaling strategies following SeNPs release from the cytoplasmic compartment, with consequent damage to SeITE01 cell membranes. This is also accompanied by intracellular accumulation of trans-4-hydroxyproline and L-proline, which likely represent osmoprotectant activity. The identification of these metabolites suggests the activation of signaling strategies that would protect the bacterial cells from SeO32- toxicity while it is converting into SeNPs.

Project description:BackgroundSelenium (Se) is an essential trace element, but is toxic at high concentrations. Depending upon the geological background, the land use or on anthropogenic pollution, different amounts of Se may be present in soil. Its toxicity is related to the oxyanions selenate and selenite as they are water soluble and bioavailable. Microorganisms play an important role in Se transformations in soil and its cycling in the environment by transforming water-soluble oxyanions into water insoluble, non-toxic elemental Se (0). For this study, soil samples were collected from selenium-contaminated agricultural soils of Punjab/India to enrich and isolate microbes that interacted with the Se cycle.ResultsA mixed microbial culture enriched from the arable soil of Punjab could reduce 230 mg/l of water soluble selenite to spherical Se (0) nanoparticles during aerobic growth as confirmed by SEM-EDX. Four pure cultures (C 1, C 4, C 6, C 7) of Gram negative, oxidase and catalase positive, aerobic bacteria were isolated from this mixed microbial consortium and identified by 16 S rDNA gene sequence alignment as two strains of Duganella sp. (C 1, C 4) and two strains of Agrobacterium sp.(C 6, C 7). SEM/TEM-EDX analyses of the culture broth of the four strains revealed excretion of uniformly round sharply contoured Se (0) nanoparticles by all cultures. Their size ranged from 140-200 nm in cultures of strains C 1 and C 4, and from 185-190 nm in cultures of strains C 6 and C 7. Both Duganella sp. revealed better selenite reduction efficiencies than the two Agrobacterium sp.ConclusionsThis is the first study reporting the capability of newly isolated, aerobically growing Duganella sp. and Agrobacterium sp. from soils of Punjab/India to form spherical, regularly formed Se (0) nanoparticles from water soluble selenite. Among others, the four strains may significantly contribute to the biogeochemical cycling of Se in soil. Bioconversion of toxic selenite to non-toxic Se (0) nanoparticles under aerobic conditions in general may be useful for detoxification of agricultural soil, since elemental Se may not be taken up by the roots of plants and thus allow non-dangerous fodder and food production on Se-containing soil.

Dataset Information

Reduction of selenite to Se(0) nanoparticles by filamentous bacterium Streptomyces sp. ES2-5 isolated from a selenium mining soil.

Publications

Reduction of selenite to Se(0) nanoparticles by filamentous bacterium Streptomyces sp. ES2-5 isolated from a selenium mining soil.

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