Antimicrobial Effect of Copper Nanoparticles on Relevant Supragingival Oral Bacteria.

Copper nanoparticles (Cu NPs) show promise in dentistry for combating bacterial dysbiosis and tooth decay. Understanding their effects on commensal versus pathogenic bacteria is vital for maintaining oral health balance. While Cu NPs demonstrate antibacterial properties against various oral bacteria, including common pathogens associated with tooth decay, their impact on commensal bacteria requires careful examination. In our work, we analyzed three types of Cu NPs for their effects on the growth, viability, and biofilm formation of representative caries-associated and commensal oral bacteria. S. sanguinis showed high tolerance to all Cu NPs, while L. rhamnosus was highly sensitive. Oxide-Cu NPs exhibited a stronger inhibitory effect on pathobionts compared with commensal bacteria. Moreover, the biofilm formation of the key cariogenic bacteria S. mutans was reduced, with minimal negative effects on commensal species' biofilm formation. All our results showed that CuO nanoparticles (CuO NPs) exhibit reduced toxicity toward commensal bacteria growth and development but have a strong impact on pathogens. This suggests their potential for targeted treatments against pathogenic bacteria, which could help in maintaining the balance of the oral bacterial community.

Correction to: A thiotrophic microbial community in an acidic brine lake in Northern Chile.

In Table 1 of the original article, the unit mg/L was incorrectly published as ng/L in the aluminum, chloride, sulphate and OM columns.

Possible Role of Envelope Components in the Extreme Copper Resistance of the Biomining Acidithiobacillus ferrooxidans.

Acidithiobacillus ferrooxidans resists extremely high concentrations of copper. Strain ATCC 53993 is much more resistant to the metal compared with strain ATCC 23270, possibly due to the presence of a genomic island in the former one. The global response of strain ATCC 53993 to copper was analyzed using iTRAQ (isobaric tag for relative and absolute quantitation) quantitative proteomics. Sixty-seven proteins changed their levels of synthesis in the presence of the metal. On addition of CusCBA efflux system proteins, increased levels of other envelope proteins, such as a putative periplasmic glucan biosynthesis protein (MdoG) involved in the osmoregulated synthesis of glucans and a putative antigen O polymerase (Wzy), were seen in the presence of copper. The expression of A. ferrooxidansmdoG or wzy genes in a copper sensitive Escherichia coli conferred it a higher metal resistance, suggesting the possible role of these components in copper resistance of A. ferrooxidans. Transcriptional levels of genes wzy, rfaE and wzz also increased in strain ATCC 23270 grown in the presence of copper, but not in strain ATCC 53993. Additionally, in the absence of this metal, lipopolysaccharide (LPS) amounts were 3-fold higher in A. ferrooxidans ATCC 53993 compared with strain 23270. Nevertheless, both strains grown in the presence of copper contained similar LPS quantities, suggesting that strain 23270 synthesizes higher amounts of LPS to resist the metal. On the other hand, several porins diminished their levels in the presence of copper. The data presented here point to an essential role for several envelope components in the extreme copper resistance by this industrially important acidophilic bacterium.

A thiotrophic microbial community in an acidic brine lake in Northern Chile.

The endorheic basins of the Northern Chilean Altiplano contain saline lakes and salt flats. Two of the salt flats, Gorbea and Ignorado, have high acidic brines. The causes of the local acidity have been attributed to the occurrence of volcanic native sulfur, the release of sulfuric acid by oxidation, and the low buffering capacity of the rocks in the area. Understanding the microbial community composition and available energy in this pristine ecosystem is relevant in determining the origin of the acidity and in supporting the rationale of conservation policies. Besides, a comparison between similar systems in Australia highlights key microbial components and specific ones associated with geological settings and environmental conditions. Sediment and water samples from the Salar de Gorbea were collected, physicochemical parameters measured and geochemical and molecular biological analyses performed. A low diversity microbial community was observed in brines and sediments dominated by Actinobacteria, Algae, Firmicutes and Proteobacteria. Most of the constituent genera have been reported to be either sulfur oxidizing microorganisms or ones having the potential for sulfur oxidation given available genomic data and information drawn from the literature on cultured relatives. In addition, a link between sulfur oxidation and carbon fixation was observed. In contrast, to acid mine drainage communities, Gorbea microbial diversity is mainly supported by chemolithoheterotrophic, facultative chemolithoautotrophic and oligotrophic sulfur oxidizing populations indicating that microbial activity should also be considered as a causative agent of local acidity.