Fluorescent nanoparticles or quantum dots (QDs) have been intensely studied for basic and applied research due to their unique size-dependent properties. There is an increasing interest in developing ecofriendly methods to synthesize these nanoparticles since they improve biocompatibility and avoid the generation of toxic byproducts. The use of biological systems, particularly prokaryotes, has emerged as a promising alternative. Recent studies indicate that QDs biosynthesis is related to factors such as cellular redox status and antioxidant defenses. Based on this, the mixture of extreme conditions of Antarctica would allow the development of natural QDs producing bacteria. In this study we isolated and characterized cadmium and tellurite resistant Antarctic bacteria capable of synthesizing CdS and CdTe QDs when exposed to these oxidizing heavy metals. A time dependent change in fluorescence emission color, moving from green to red, was determined on bacterial cells exposed to metals. Biosynthesis was observed in cells grown at different temperatures and high metal concentrations. Electron microscopy analysis of treated cells revealed nanometric electron-dense elements and structures resembling membrane vesicles mostly associated to periplasmic space. Purified biosynthesized QDs displayed broad absorption and emission spectra characteristic of biogenic Cd nanoparticles. Our work presents a novel and simple biological approach to produce QDs at room temperature by using heavy metal resistant Antarctic bacteria, highlighting the unique properties of these microorganisms as potent natural producers of nano-scale materials and promising candidates for bioremediation purposes.

The present study examined the biosynthesis and characterization of selenium nanoparticles (SeNPs) using two contrasting endophytic selenobacteria, one Gram-positive (Bacillus sp. E5 identified as Bacillus paranthracis) and one Gram-negative (Enterobacter sp. EC5.2 identified as Enterobacter ludwigi), for further use as biofortifying agents and/or for other biotechnological purposes. We demonstrated that, upon regulating culture conditions and selenite exposure time, both strains were suitable “cell factories” for producing SeNPs (B-SeNPs from B. paranthracis and E-SeNPs from E. ludwigii) with different properties. Briefly, dynamic light scattering (DLS), transmission electron microscopy (TEM), and atomic force microscopy (AFM) studies revealed that intracellular E-SeNPs (56.23 ± 4.85 nm) were smaller in diameter than B-SeNPs (83.44 ± 2.90 nm) and that both formulations were located in the surrounding medium or bound to the cell wall. AFM images indicated the absence of relevant variations in bacterial volume and shape and revealed the existence of layers of peptidoglycan surrounding the bacterial cell wall under the conditions of biosynthesis, particularly in the case of B. paranthracis. Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), energy-dispersive X-ray (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) showed that SeNPs were surrounded by the proteins, lipids, and polysaccharides of bacterial cells and that the numbers of the functional groups present in B-SeNPs were higher than in E-SeNPs. Thus, considering that these findings support the suitability of these two endophytic stains as potential biocatalysts to produce high-quality Se-based nanoparticles, our future efforts must be focused on the evaluation of their bioactivity, as well as on the determination of how the different features of each SeNP modulate their biological action and their stability.

Use of microorganisms in contaminated water remediation is one of the most studied processes of recent years. The recovery of metal contaminants by converting them into high-value nanomaterials represents a scarcely explored topic with high potential economic impact. In this work, the authors determine the capacity to remove As and Cd from aqueous solutions by Antarctic bacteria previously reported as capable of biosynthesizing CdS fluorescent nanoparticles (NPs) at low temperatures. Bacterial characteristics favoring metal bioremediation, such as As and Cd resistance as well as high biofilm formation and metal removal (kinetic/sorption tests), were determined in Antarctic strains. In addition, the effect of As on the biosynthesis of CdS fluorescent NPs [quantum dots (QDs)] was evaluated. The presence of As inhibits the biosynthesis of CdS QDs by Antarctic bacteria. Arsenic inhibition does not involve the disruption of the Cd nanostructure or a decrease in ${\mathrm{H}}_2\mathrm{S}$ levels produced by cells, suggesting that As inhibits CdS biosynthesis by avoiding the interaction of ${\mathrm{Cd}}^{2+}$ with ${\mathrm{S}}^{2-}$ required to produce the nanocrystal. Obtained results have significant consequences for the development of metal bioremediation strategies aimed at removing environmental heavy metals through the generation of NPs.

Here, we present the draft genome sequence of Pseudomonas sp. GC01, a cadmium-resistant Antarctic bacterium capable of biosynthesizing CdS fluorescent nanoparticles (quantum dots, QDs) employing a unique mechanism involving the production of methanethiol (MeSH) from methionine (Met). To explore the molecular/metabolic components involved in QDs biosynthesis, we conducted a comparative genomic analysis, searching for the genes related to cadmium resistance and sulfur metabolic pathways. The genome of Pseudomonas sp. GC01 has a 4,706,645 bp size with a 58.61% G+C content. Pseudomonas sp. GC01 possesses five genes related to cadmium transport/resistance, with three P-type ATPases (cadA, zntA, and pbrA) involved in Cd-secretion that could contribute to the extracellular biosynthesis of CdS QDs. Furthermore, it exhibits genes involved in sulfate assimilation, cysteine/methionine synthesis, and volatile sulfur compounds catabolic pathways. Regarding MeSH production from Met, Pseudomonas sp. GC01 lacks the genes E4.4.1.11 and megL for MeSH generation. Interestingly, despite the absence of these genes, Pseudomonas sp. GC01 produces high levels of MeSH. This is probably associated with the metC gene that also produces MeSH from Met in bacteria. This work is the first report of the potential genes involved in Cd resistance, sulfur metabolism, and the process of MeSH-dependent CdS QDs bioproduction in Pseudomonas spp. strains.

Rhodococcus species display remarkable metabolic versatility and adaptation to extreme environments, yet their antimicrobial potential remains largely unexplored, particularly in strains representing undescribed genomic lineages. This study investigated whether the genome of Rhodococcus sp. GB-02, a strain isolated from Antarctic soil, encodes antimicrobial peptides with demonstrable activity against clinically relevant pathogens. Hybrid genome assembly revealed a 6.58 Mb high-quality draft genome belonging to a previously undescribed genomic lineage within the genus Rhodococcus, based on average nucleotide identity and digital DNA–DNA hybridization analyses. Genome mining identified 20 biosynthetic gene clusters, predominantly non-ribosomal peptide synthetases, several of which showed low or no similarity to known pathways. Eight putative antimicrobial peptides (AMPs) were computationally predicted; among these, three lacked detectable homology to sequences in current databases, and experimental validation of one predicted peptide, designated Peptide 5764, demonstrated antibacterial activity at high micromolar concentrations against Gram-positive and Gram-negative pathogens and concentration-dependent inhibition of biofilm formation, particularly in Pseudomonas aeruginosa. However, Peptide 5764 exhibited considerable hemolytic activity at antibacterial concentrations, indicating that optimization for membrane selectivity will be required before therapeutic application. These findings establish Rhodococcus sp. GB-02 as an underexplored Antarctic lineage with a diverse biosynthetic repertoire and provide proof-of-concept that genome-guided AMP prediction can identify experimentally active peptide scaffolds from this lineage.