Minicells as an Escherichia coli mechanism for the accumulation and disposal of fluorescent cadmium sulphide nanoparticles.

BACKGROUND: Bacterial biosynthesis of fluorescent nanoparticles or quantum dots (QDs) has emerged as a unique mechanism for heavy metal tolerance. However, the physiological pathways governing the removal of QDs from bacterial cells remains elusive. This study investigates the role of minicells, previously identified as a means of eliminating damaged proteins and enhancing bacterial resistance to stress. Building on our prior work, which unveiled the formation of minicells during cadmium QDs biosynthesis in Escherichia coli, we hypothesize that minicells serve as a mechanism for the accumulation and detoxification of QDs in bacterial cells. RESULTS: Intracellular biosynthesis of CdS QDs was performed in E. coli mutants ΔminC and ΔminCDE, known for their minicell-producing capabilities. Fluorescence microscopy analysis demonstrated that the generated minicells exhibited fluorescence emission, indicative of QD loading. Transmission electron microscopy (TEM) confirmed the presence of nanoparticles in minicells, while energy dispersive spectroscopy (EDS) revealed the coexistence of cadmium and sulfur. Cadmium quantification through flame atomic absorption spectrometry (FAAS) demonstrated that minicells accumulated a higher cadmium content compared to rod cells. Moreover, fluorescence intensity analysis suggested that minicells accumulated a greater quantity of fluorescent nanoparticles, underscoring their efficacy in QD removal. Biosynthesis dynamics in minicell-producing strains indicated that biosynthesized QDs maintained high fluorescence intensity even during prolonged biosynthesis times, suggesting continuous QD clearance in minicells. CONCLUSIONS: These findings support a model wherein E. coli utilizes minicells for the accumulation and removal of nanoparticles, highlighting their physiological role in eliminating harmful elements and maintaining cellular fitness. Additionally, this biosynthesis system presents an opportunity for generating minicell-coated nanoparticles with enhanced biocompatibility for diverse applications.

Pseudomonas violetae sp. nov. and Pseudomonas emilianonis sp. nov., two new species with the ability to degrade TNT isolated from soil samples at Deception Island, maritime Antarctica.

Two motile, rod-shaped, Gram-stain-negative bacterial strains, TNT11T and TNT19T, were isolated from soil samples collected at Deception Island, Antarctica. According to the 16S rRNA gene sequence similarity, both strains belong to the genus Pseudomonas. Further genomic analyses based on ANI and dDDH suggested that these strains were new species. Growth of strain TNT11T is observed at 0-30 â„ƒ (optimum, 20 â„ƒ), pH 4.0-9.0 (optimum, pH 6.0) and in the presence of 0-5.0% NaCl (optimum, 1% NaCl), while for TNT19T is observed at 0-30 â„ƒ (optimum between 15 and 20 â„ƒ), pH 5.0-9.0 (optimum, pH 6.0) and in the presence of 0-5.0% NaCl (optimum between 0 and 1% NaCl). The fatty acid profile consists of the major compounds; C16:0 and C16:1 ω6 for TNT11T, and C16:0 and C12:0 for TNT19T. Based on the draft genome sequences, the DNA G + C content for TNT11T is 60.43 mol% and 58.60 mol% for TNT19T. Based on this polyphasic study, TNT11T and TNT19T represent two novel species of the genus Pseudomonas, for which the proposed names are Pseudomonas violetae sp. nov. and Pseudomonas emilianonis sp. nov., respectively. The type strains are Pseudomonas violetae TNT11T (= RGM 3443T = LMG 32959T) and Pseudomonas emilianonis TNT19T (= RGM 3442T = LMG 32960T). Strains TNT11T and TNT19T were deposited to CChRGM and BCCM/LMG with entry numbers RGM 3443/LMG 32959 and RGM 3442/LMG 32960, respectively.

Arthrobacter vasquezii sp. nov., isolated from a soil sample from Union Glacier, Antarctica.

A Gram-stain-positive, catalase-positive, non-motile bacteria, with a rod-coccus cycle (designated as EH-1B-1T) was isolated from a soil sample from Union Glacier in Ellsworth Mountains, Antarctica. Strain EH-1B-1T had an optimal growth temperature of 28 °C and grew at pH 7-10. The major cellular fatty acids were anteiso-C15 : 0, iso-C15 : 0, C16 : 0 and anteiso-C17 : 0. The G+C content based on the whole genome sequence was 63.1 mol%. Strain EH-1B-1T was most closely related to members of the genus Arthrobacter, namely Arthrobacter subterraneus and Arthrobacter tumbae. The strain grew on tryptic soy agar, Reasoner's 2A agar, lysogeny broth agar and nutrient agar. The average nucleotide identity and digital DNA-DNA hybridization values between strain EH-1B-1T and its closest reference type strains ranged from 78 to 88 % and from 20.9 to 36.3 %, respectively. Based on phenotypic, chemotypic and genotypic evidence, it is proposed that strain EH-1B-1T represents a novel species of Arthrobacter, for which the name Arthrobacter vasquezii sp. nov. is proposed, with strain EH-1B-1T (RGM 3386T=LMG 32961T) as the type strain.

Solid medium for the direct isolation of bacterial colonies growing with polycyclic aromatic hydrocarbons or 2,4,6-trinitrotoluene (TNT).

Isolation of hydrocarbon-degrading bacteria is a key step for the study of microbiological diversity, metabolic pathways, and bioremediation. However current strategies lack simplicity and versatility. We developed an easy method for the screening and isolation of bacterial colonies capable of degrading hydrocarbons, such as diesel or polycyclic aromatic hydrocarbons (PAHs), as well as the pollutant explosive, 2,4,6-trinitrotoluene (TNT). The method uses a two-layer solid medium, with a layer of M9 medium, and a second layer containing the carbon source deposited through the evaporation of ethanol. Using this medium we grew hydrocarbon-degrading strains, as well as TNT-degrading isolates. We were able to isolate PAHs-degrading bacterial colonies directly from diesel-polluted soils. As a proof of concept, we used this method to isolate a phenanthrene-degrading bacteria, identified as Acinetobacter sp. and determined its ability to biodegrade this hydrocarbon.