Ochrobactrum sp. MPV1 from a dump of roasted pyrites can be exploited as bacterial catalyst for the biogenesis of selenium and tellurium nanoparticles

Background: Bacteria have developed different mechanisms for the transformation of metalloid oxyanions to non-toxic chemical forms. A number of bacterial isolates so far obtained in axenic culture has shown the ability to bioreduce selenite and tellurite to the elemental state in different conditions along with the formation of nanoparticles-both inside and outside the cells-characterized by a variety of morphological features. This reductive process can be considered of major importance for two reasons: firstly, toxic and soluble (i.e. bioavailable) compounds such as selenite and tellurite are converted to a less toxic chemical forms (i.e. zero valent state); secondly, chalcogen nanoparticles have attracted great interest due to their photoelectric and semiconducting properties. In addition, their exploitation as antimicrobial agents is currently becoming an area of intensive research in medical sciences. Results: In the present study, the bacterial strain Ochrobactrum sp. MPV1, isolated from a dump of roasted arsenopyrites as residues of a formerly sulfuric acid production near Scarlino (Tuscany, Italy) was analyzed for its capability of efficaciously bioreducing the chalcogen oxyanions selenite (SeO32-) and tellurite (TeO32-) to their respective elemental forms (Se0 and Te0) in aerobic conditions, with generation of Se- and Te-nanoparticles (Se- and TeNPs). The isolate could bioconvert 2 mM SeO32- and 0.5 mM TeO32- to the corresponding Se0 and Te0 in 48 and 120 h, respectively. The intracellular accumulation of nanomaterials was demonstrated through electron microscopy. Moreover, several analyses were performed to shed light on the mechanisms involved in SeO32- and TeO32- bioreduction to their elemental states. Results obtained suggested that these oxyanions are bioconverted through two different mechanisms in Ochrobactrum sp. MPV1. Glutathione (GSH) seemed to play a key role in SeO32- bioreduction, while TeO32- bioconversion could be ascribed to the catalytic activity of intracellular NADH-dependent oxidoreductases. The organic coating surrounding biogenic Se- and TeNPs was also characterized through Fourier-transform infrared spectroscopy. This analysis revealed interesting differences among the NPs produced by Ochrobactrum sp. MPV1 and suggested a possible different role of phospholipids and proteins in both biosynthesis and stabilization of such chalcogen-NPs. Conclusions: In conclusion, Ochrobactrum sp. MPV1 has demonstrated to be an ideal candidate for the bioconversion of toxic oxyanions such as selenite and tellurite to their respective elemental forms, producing intracellular Se- and TeNPs possibly exploitable in biomedical and industrial applications.[Figure not available: see fulltext.

Antimicrobial activity of biogenically produced spherical Se-nanomaterials embedded in organic material against Pseudomonas aeruginosa and Staphylococcus aureus strains on hydroxyapatite-coated surfaces

In an effort to prevent the formation of pathogenic biofilms on hydroxyapatite (HA)-based clinical devices and surfaces, we present a study evaluating the antimicrobial efficacy of Spherical biogenic Se-Nanostructures Embedded in Organic material (Bio Se-NEMO-S) produced by Bacillus mycoides SelTE01 in comparison with two different chemical selenium nanoparticle (SeNP) classes. These nanomaterials have been studied as potential antimicrobials for eradication of established HA-grown biofilms, for preventing biofilm formation on HA-coated surfaces and for inhibition of planktonic cell growth of Pseudomonas aeruginosa NCTC 12934 and Staphylococcus aureus ATCC 25923. Bio Se-NEMO resulted more efficacious than those chemically produced in all tested scenarios. Bio Se-NEMO produced by B. mycoides SelTE01 after 6 or 24 h of Na 2 SeO 3 exposure show the same effective antibiofilm activity towards both P. aeruginosa and S. aureus strains at 0.078 mg ml −1 (Bio Se-NEMO 6 ) and 0.3125 mg ml −1 (Bio Se-NEMO 24 ). Meanwhile, chemically synthesized SeNPs at the highest tested concentration (2.5 mg ml −1 ) have moderate antimicrobial activity. The confocal laser scanning micrographs demonstrate that the majority of the P. aeruginosa and S. aureus cells exposed to biogenic SeNPs within the biofilm are killed or eradicated. Bio Se-NEMO therefore displayed good antimicrobial activity towards HA-grown biofilms and planktonic cells, becoming possible candidates as new antimicrobials

Reduction of chalcogen oxyanions and biogenesis of nanoparticles by Ochrobactrum sp. MPV1

Metal nanoparticles have been produced using chemical and physical methods for many years. However, the exploitation of strong reducing agents may lead to undesired toxicity issues. It is, therefore, important to develop alternative and ecofriendly methods . Recently biosynthetic methods employing microorganisms have emerged as simple and viable alternative to produce metal/metalloid nanoparticles. In particular, the chalcogens selenium and tellurium in their elemental forms exhibited interesting antimicrobi al activity. Moreover, nanoparticles produced with these elements show intriguing optoelectronic and semiconducting properties

Extracellular synthesis of selenium nanospheres by Bacillus mycoides strain SeITE01

A bacterial strain (SeITE01), isolated from the rhizosphere of the selenium hyperaccumulator legume Astragalus bisulcatus [1] and identified as Bacillus mycoides, was studied for its ability to efficiently reduce selenite to elemental selenium in aerobic conditions and consequently to produce elemental selenium nanospheres. The isolate exhibited significant tolerance to selenite (SeO32-) up to 30mM in oxyanion concentration. SeITE01 was incubated with both 0.5 and 2mM Na2SeO3, performing the complete reduction of selenite respectively within 12 and 24 hours. The strain converted 91% of the initial selenite added to the culture medium into elemental selenium with cultures developing a deep red color characteristic of crystalline Se0. Characterization of red Se0 precipitate by using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and UV-Vis spectroscopy revealed the presence of extracellular spherical nanoparticles. The sizes of these nanoparticles range from 200 to 250 nm in bacterial cultures after 24 hours of exposure to selenite. Moreover, after 48 hours, the nanoparticles reach a diameter of 1\u3bcm. EDX analysis of the same particles revealed the characteristic peaks of selenium absorption at 1.37 keV (SeL\u3b1), 11.22 keV (SeK\u3b1) and 12.49 keV (SeK\u3b2), respectively. Selenite reduction activity was observed mainly in membrane proteins and even in the exoenzymatic fraction. Therefore, a hypothetical mechanism for the synthesis of selenium nanoparticles has been proposed

Stenotrophomonas sp. exopolysaccharides produced during aerobic growth can reduce selenite to red elemental selenium

Different Stenotrophomonas sp. strains \u2013 namely SelTE02, B, T, A16, and AW - able to reduce selenite to elemental selenium in aerobic conditions were isolated from soil. Several Stenotrophomonas strains are reported in scientific literature to be able to produce EPS. In the present study, EPS production by the different Stenotrophomonas isolates at increasing selenite concentrations (i.e. 0.2, 0.5, and 2 mM respectively) was measured to evaluate the possible influence of this oxyanion on exopolysaccharide formation

Bacterial biosynthesis of selenium nanoparticles by environmental isolates of Stenotrophomonas maltophilia

Five bacterial strains identified in soil samples collected at three dismissed industrial sites contaminated by heavy metals and metalloids such as lead, arsenic, and selenium were analysed for their capability to reduce the toxic oxyanion selenite (SeO32-) to the non-toxic zerovalent selenium. All isolates resulted taxonomically related to the Stenotrophomonas maltophilia species and capable of forming Senanopaticles (SeNPs)

Se and Te nanoparticles biosynthesized by bacteria as antimicrobial agents against human pathogens

In the present work, Se0 and Te0-based nanoparticles were bio-synthesized employing the selenite and tellurite-reducing capability different bacterial strains. By regulating culture conditions and exposition time, we were able to produce nanoparticles of different dimensions, between 50 and 200nm. Our results indicate that both Se0 and Te0 nanoparticles possess antimicrobial and biofilm eradication activity against Escherichia coli JM109, Pseudomonas aeruginosa PAO1 and Staphylococcus aureus ATCC 25923. Preliminary data suggests that the activity seemed to be dependent on the dimension of the nanoparticles: indeed, the highest activity was shown by the nanoparticles smaller in size. The key observation is that bacteria growth in biofilm mode didn\u2019t exhibit a higher level of resistance against the nanoparticles antimicrobial action. - See more at: http://2014.nanotechitaly.it/abstracts/se-and-te-nanoparticles-biosynthesized-by-bacteria-as-antimicrobial-agents-against-human-pathogens/#sthash.aCTfsSEX.dpu