Littérature scientifique sur le sujet « Stenotrophomonas maltophilia SeITE02 »

ABSTRACT Biochemical and proteomic tools have been utilized for investigating the mechanism of action of a new Stenotrophomonas maltophilia strain (SeITE02), a gammaproteobacterium capable of resistance to high concentrations of selenite [SeO3 2−, Se(IV)], reducing it to nontoxic elemental selenium under aerobic conditions; this strain was previously isolated from a selenite-contaminated mining soil. Biochemical analysis demonstrated that (i) nitrite reductase does not seem to take part in the process of selenite reduction by the bacterial strain SeITE02, although its involvement in this process had been hypothesized in other cases; (ii) nitrite strongly interferes with selenite removal when the two oxyanions (NO2 − and SeO3 2−) are simultaneously present, suggesting that the two reduction/detoxification pathways share a common enzymatic step, probably at the level of cellular transport; (iii) in vitro, selenite reduction does not take place in the membrane or periplasmic fractions but only in the cytoplasm, where maximum activity is exhibited at pH 6.0 in the presence of NADPH; and (iv) glutathione is involved in the selenite reduction mechanism, since inhibition of its synthesis leads to a considerable delay in the onset of reduction. As far as the proteomic findings are concerned, the evidence was reached that 0.2 mM selenite and 16 mM nitrite, when added to the culture medium, caused a significant modulation (ca. 10%, i.e., 96 and 85 protein zones, respectively) of the total proteins visualized in the respective two-dimensional maps. These spots were identified by mass spectrometry analysis and were found to belong to the following functional classes: nucleotide synthesis and metabolism, damaged-protein catabolism, protein and amino acid metabolism, and carbohydrate metabolism along with DNA-related proteins and proteins involved in cell division, oxidative stress, and cell wall synthesis.

AbstractVarious technological and biomedical applications rely on the ability of materials to emit light (photoluminescence [PL]), and, among them, metal nanoparticles (NPs) and semi-conductor Quantum Dots (QDs) represent ideal candidates as sensing probes and imaging tools, portraying better PL features than conventional organic dyes. However, the knowledge of PL behavior of semiconductor NPs – i.e., selenium; SeNPs – is still in its infancy, especially for those synthesized by microorganisms. Considering the essential role played by biogenic SeNPs as antimicrobial, anticancer, and antioxidant agents, or food supplements, their PL properties must be explored to take full advantage of them as eco-friendly and versatile tools. Here, PL features of SeNPs produced by the Se-tolerant Stenotrophomonas maltophilia SeITE02 strain, compared with chemogenic ones, are investigated, highlighting the PL dependency on the NP size. Indeed, PL emission shifted from indigo-blue (emission wavelength λem 400–450 nm) to green-yellow (λem 480–570 nm) and orange-red (λem 580–700 nm) for small (ca. 50 nm) and big (ca. 100 nm) SeNPs respectively, revealing the versatility of an environmental bacterial isolate to synthesize diverse PL probes. Besides, biogenic SeNPs show PL lifetime comparable to those of the most used fluorophores, supporting their potential application as markers for (bio)imaging.

Bacillus mycoides SeITE01 and Stenotrophomonas maltophilia SeITE02 are environmental bacterial isolates that rely on detoxification processes to transform selenite (SeO32-), a highly toxic and bioavailable chemical species of selenium, into insoluble and virtually nontoxic elemental selenium (Se0) with the formation of biogenic selenium nanoparticles (Bio-SeNPs). In the last decade, Bio-SeNPs have attracted attention for their interesting applications in the nanotechnology, industrial and medical fields not only due to their special physico-chemical features, but also for their attractive antimicrobial activities and anticancer properties. These worthwhile biotechnological traits are related to the presence on Bio-SeNPs of an external organic coating, whose composition and role are mostly unknown and currently under investigation. In the first part of this thesis, FTIR (Fourier Transform Infrared) spectroscopy was applied to study the SeO32- bio-reduction process analysing the bio-molecular composition of both SeITE01 and SeITE02 cells. The analysis was conducted during the diverse cellular growth phases and in different conditions, namely untreated (growth without the presence in the medium of sodium selenite Na2SeO3) and Se-treated (exposure to the stress factor SeO32-). Moreover, along with FTIR spectroscopic analyses, the biogenic intracellular and extracellular SeNPs bio-produced by the bacterial strains and collected with two extraction methods (vacuum filtration and pelleting processing) were examined also using DLS (Dynamic Light Scattering) measurements and TEM (Transmission Electron Microscopy) imaging. In the second part of this research, metabolomics was used to investigate the biological reduction and effect of Na2SeO3 on SeITE01 and SeITE02 cells by a LC-MS (Liquid Chromatography Mass-Spectrometry) approach. Both intracellular and extracellular metabolites and their concentration fluxes during a defined time course and in response to the exposure of bacterial cells to SeO32- were studied. From the results obtained with all the investigation techniques it was possible to observe and underline two distinct behaviors and trends assumed by the bacterial strains. SeITE01 cells showed substantial changes when exposed to SeO32-, activating a series of macromolecular responses and biochemical pathways to defend the cells against the toxic action of both the oxyanion and the Se nanostructures. Moreover, different FTIR spectral trends were acquired with regard to the organic coatings present on the surfaces of the biogenic SeNPs synthesized by this bacterium, and the most marked differences were recorded according to their different localization (intracellular or extracellular). The Bio-SeNPs production in this Gram-positive microorganism was also described by the data collected with the DLS and the zeta-potential measurements. The analyzed Bio-SeNPs showed an average dimension between 637 and 393 nm for the intracellular Bio-SeNPs, and 147 nm for the extracellular ones. Low value of negative potentials suggest a lower stability of these nanostructures in solution. On the contrary, the Gram-negative bacterium SeITE02 did not present drastic changes in the macromolecular composition after SeO32- exposure, and the variations recorded were mainly due to the maintenance of vital cellular functions. DLS data revealed an average size of 315 nm for the intracellular Bio-SeNPs and 160 nm for the extracellular ones, whilst negative potential values at or below -30 mV were recorded, indicating a remarkable stability of these biogenic Se nanostructures and a lower tendency to form aggregates and thus to precipitate. Thus, the results obtained in the course of this investigation revealed two distinct attitudes and responses on the part of the two microorganisms SeITE01 and SeITE02 to the SeO32- exposure and Bio-SeNPs production.