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Selenium nanoparticle synthesis in Stenotrophomonas maltophilia: Mutagenesis and molecular mechanisms.

Biosynthetic selenium nanoparticles (SeNPs) exhibit superior bioavailability and detoxification potential compared to inorganic selenium forms. In this study, the strain Stenotrophomonas maltophilia SE5, isolated from the feces of piglets (Duroc × Large White × Landrace), was utilized as the wild-type strain and subjected to atmospheric and room temperature plasma (ARTP) mutagenesis. A high-yielding mutant, Mu537, was successfully obtained, which exhibited an enhanced tolerance to sodium selenite, with its maximum tolerable concentration increasing from 1.0 g/L to 1.5 g/L. After 48 h of cultivation, Mu537 achieved an approximate 35% increase in SeNPs conversion rate and a 40% increase in SeNPs concentration relative to the parental strain. Integrated whole-genome sequencing and transcriptomic analysis revealed that pivotal genes associated with efficient SeNPs biosynthesis, including cysB, trxA, and sufE, were significantly up-regulated. These findings provide a systematic understanding of the potential molecular mechanisms driving enhanced SeNPs biosynthesis, offering both high-quality microbial resources and theoretical support for the industrial production of SeNPs.

Stenotrophomonas maltophilia

Integrated Optimization, Genomic Characterization, and Functional Evaluation of Biogenic Selenium Nanoparticles from Bacillus licheniformis BLN313: Antibacterial and Anticancer Potential.

Microbial synthesis of selenium nanoparticles (SeNPs) offers a sustainable alternative to chemical routes, but the genetic basis of selenium handling in Bacillus remains poorly defined, which limits rational strain selection. Here, SeNP production, physicochemical characterization, and closed-genome sequencing are combined for Bacillus licheniformis BLN313. Selenite reduction peaked at 500 µg/mL Na2SeO3 (88.8% conversion; 444 ± 27 µg/mL Se0); at higher concentrations, conversion efficiency and viability diverged, indicating that tolerance and reductive capacity are distinct traits. Purified SeNPs were spherical and partially crystalline trigonal Se0 (TEM 190 ± 52 nm; DLS 166 nm, PDI 0.03; zeta potential -20.8 mV), carrying a proteinaceous capping layer confirmed by XPS, EDS, and FTIR and shown by LC-MS to be enriched in cell wall-derived metabolites. The particles were bactericidal against Micrococcus luteus (MIC 62.5 µg/mL) and Klebsiella pneumoniae (MIC 250 µg/mL) and reduced MCF-7 viability (IC50 2.7 µg/mL) while sparing MCF-10A cells. The 4.11 Mb genome (46.3% GC; ANI 99.7%, dDDH 97.8%) encodes SulP and Pit transporters, multiple trxB copies, and sulfur-metabolism and oxidative-stress genes, defining a candidate gene set for selenium uptake, reduction and detoxification. BLN313 thus provides a genetically defined platform for SeNP production in biomedical and environmental applications.

Selenium

Salinimicrobium molybdatiresistens sp. nov., a novel molybdate-resistant and selenite-reducing bacterium isolated from river silt.

Strain TH3T was isolated from the river bottom silt collected in Hengshui, Hebei Province, China. The bacterium is a yellow-pigmented, rod-shaped, Gram-staining negative and aerobic organism. It was able to grow between 10 and 37 °C (optimum 30 °C), at pH values from 5.0 to 9.0 (optimum pH 7.0), and tolerated NaCl concentrations ranging from 0 to 13% (w/v, optimum 2%). The 16 S rRNA gene sequence of strain TH3T was found to be most closely related to Salinimicrobium sediminilitoris ASW11-47T (99.7%). Nevertheless, genome comparison revealed the relatedness indices below species delineation thresholds: digital DNA-DNA hybridization was 49.7%, and average nucleotide identity was 93.2%, and average amino acid identity was 94.2% compared to Salinimicrobium sediminilitoris ASW11-47T. Strain TH3T had a genome size of 3.7 Mb and a DNA G + C content of 41.0%. The major fatty acids observed for strain TH3T (≥ 5%) were iso-C14:0, iso-C15:0, anteiso-C15:0, iso-C16:0, iso-C16:0 3-OH, iso-C17:0 3-OH, and summed feature 3. The polar lipid composition included phosphatidylethanolamine, one unidentified phospholipid, two aminolipids, along with five unknown lipids. The sole respiratory quinone in strain TH3T was menaquinone-6. In addition, strain TH3T was highly resistant to molybdate (500 mM) and selenite (20 mM), and could completely reduce 1 mM selenite to red elemental SeNPs within 3 d. Strain TH3T contains several putative selenite-reducing genes, including sodA, serA, serC, cysH, deoC, tktA, and pdhC. Based on polyphasic characterization, strain TH3T was found to be a novel species in the genus Salinimicrobium, and the proposed name is Salinimicrobium molybdatiresistens sp. nov. The type strain is TH3T (= GDMCC 1.3399T = JCM 35713T).

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