Debora F. Rodrigues

Antibacterial effects of carbon nanotubes: size does matter!

We provide the first evidence that the size (diameter) of carbon nanotubes (CNTs) is a key factor governing their antibacterial effects and that the likely main CNT-cytotoxicity mechanism is cell membrane damage by direct contact with CNTs. Experiments with well-characterized single-walled carbon nanotubes (SWNTs) and multiwalled carbon nanotubes (MWNTs) demonstrate that SWNTs are much more toxic to bacteria than MWNTs. Gene expression data show that in the presence of both MWNTs and SWNTs, Escherichia coli expresses high levels of stress-related gene products, with the quantity and magnitude of expression being much higher in the presence of SWNTs.

Toxic Effects of Single-Walled Carbon Nanotubes in the Development of E. coli Biofilm

The impact of single-walled carbon nanotubes (SWNTs) on the different developmental stages of biofilms has been investigated using E. coli K12 as a model organism. Specifically, we investigated (i) the impact of SWNT concentration on cell growth and biofilm formation, (ii) toxic effects of SWNTs on mature biofilms, and (iii) formation of biofilm on SWNT-coated surfaces. The results show that at the initial stage of biofilm formation, SWNTs come into contact with bacterial cells prior to biofilm maturation and inhibit their growth. Furthermore, the results suggest that bacteria in mature biofilms are less sensitive to the presence of SWNTs than cells in other biofilm stages, similar to previous observations of biofilm resistance to antimicrobials. In mature biofilms, the soluble exopolymeric substances (EPS) secreted by the biofilm play an important role in mitigating the toxic effects of SWNTs. Upon exposure to SWNTs, biofilms without soluble EPS in the supernatant had a much more significant loss of biomass because of cell detachment from the biofilm than biofilms containing soluble EPS. To observe similar cell loss, biofilms with soluble EPS needed SWNT concentrations that were 10 times higher compared to biofilms without soluble EPS. Finally, SWNTs deposited onto surfaces affected significantly the subsequent biofilm development. Analysis of the total biomass and the area occupied by cells indicates that a SWNT-coated substratum has 10 times less biofilm colonization and biomass production than a control substratum without SWNTs.

Investigation of acute effects of graphene oxide on wastewater microbial community: A case study

The market for graphene-based products, such as graphene oxide (GO), is projected to reach nearly

Coping with Our Cold Planet

675 million by 2020, hence it is expected that large quantities of graphene-based wastes will be generated by then. Wastewater treatment plants will be one of the ultimate repositories for these wastes. Efficient waste treatment relies heavily on the functions of diverse microbial communities. Therefore, systematic investigation of any potential toxic effects of GO in wastewater microbial communities is essential to determine the potential adverse effects and the fate of these nanomaterials in the environment. In the present study, we investigate the acute toxicity, i.e. short-term and high load, effect of GO on the microbial functions related to the biological wastewater treatment process. The results showed that toxic effects of GO on microbial communities were dose dependent, especially in concentrations between 50 and 300mg/L. Bacterial metabolic activity, bacterial viability, and biological removal of nutrients, such as organics, nitrogen and phosphorus, were significantly impacted by the presence of GO in the activated sludge. Furthermore, the presence of GO deteriorated the final effluent quality by increasing the water turbidity and reducing the sludge dewaterability. Microscopic techniques confirmed penetration and accumulation of GO inside the activated sludge floc matrix. Results demonstrated that the interaction of GO with wastewater produced significant amount of reactive oxygen species (ROS), which could be one of the responsible mechanisms for the toxic effect of GO.

Antimicrobial graphene polymer (PVK-GO) nanocomposite films

Of all the natural stress conditions on our planet and in our solar system, cold is arguably the most widespread, at least from the perspective of mesophilic and thermophilic organisms. For instance, 90% of the Earths oceans have a temperature of 5°C or less. When terrestrial habitats are included

The Genome Sequence of Psychrobacter arcticus 273-4, a Psychroactive Siberian Permafrost Bacterium, Reveals Mechanisms for Adaptation to Low-Temperature Growth

The first report on the fabrication and application of a nanocomposite containing poly-N-vinyl carbazole (PVK) polymer and graphene oxide (GO) as an antimicrobial film was demonstrated. The antimicrobial film was 90% more effective in preventing bacterial colonization relative to the unmodified surface. More importantly, the nanocomposite thin film showed higher bacterial toxicity than pure GO-modified surface.

Graphene nanocomposite for biomedical applications: fabrication, antimicrobial and cytotoxic investigations

ABSTRACT Psychrobacter arcticus strain 273-4, which grows at temperatures as low as −10°C, is the first cold-adapted bacterium from a terrestrial environment whose genome was sequenced. Analysis of the 2.65-Mb genome suggested that some of the strategies employed by P. arcticus 273-4 for survival under cold and stress conditions are changes in membrane composition, synthesis of cold shock proteins, and the use of acetate as an energy source. Comparative genome analysis indicated that in a significant portion of the P. arcticus proteome there is reduced use of the acidic amino acids and proline and arginine, which is consistent with increased protein flexibility at low temperatures. Differential amino acid usage occurred in all gene categories, but it was more common in gene categories essential for cell growth and reproduction, suggesting that P. arcticus evolved to grow at low temperatures. Amino acid adaptations and the gene content likely evolved in response to the long-term freezing temperatures (−10°C to −12°C) of the Kolyma (Siberia) permafrost soil from which this strain was isolated. Intracellular water likely does not freeze at these in situ temperatures, which allows P. arcticus to live at subzero temperatures.

Architecture of thermal adaptation in an Exiguobacterium sibiricum strain isolated from 3 million year old permafrost: A genome and transcriptome approach

Materials possessing excellent bacterial toxicity, while presenting low cytotoxicity to human cells, are strong candidates for biomaterials applications. In this study, we present the fabrication of a nanocomposite containing poly(N-vinylcarbazole) (PVK) and graphene (G) in solutions and thin films. Highly dispersed PVK-G (97-3 w/w%) solutions in various organic and aqueous solvents were prepared by solution mixing and sonication methods. The thermal properties and morphology of the new composite were analyzed using thermal gravimetry analysis (TGA) and atomic force microscopy (AFM), respectively. PVK-G films were immobilized onto indium tin oxide (ITO) substrates via electrodeposition. AFM was used to characterize the resulting topography of the nanocomposite thin films, while cyclic voltammetry and UV-vis were used to monitor their successful electrodeposition. The antimicrobial properties of the electrodeposited PVK-G films and solution-based PVK-G were investigated against Escherichia coli (E. coli) and Bacillus subtilis (B. subtilis). Microbial growth after exposure to the nanocomposite, metabolic assay and live-dead assay of the bacterial solutions exposed to PVK-G presented fewer viable and active bacteria than those exposed to pure PVK or pure graphene solutions. The PVK-G film inhibited about 80% of biofilm surface coverage whereas the PVK- and G-modified surfaces allowed biofilm formation over almost the whole coated surface (i.e. > 80%). The biocompatibility of the prepared PVK-G solutions on NIH 3T3 cells was evaluated using the MTS cell proliferation assay. A 24 h exposure of the PVK-G nanocomposite to the NIH 3T3 cells presented ~80% cell survival.

Toxicity of Functionalized Single-Walled Carbon Nanotubes on Soil Microbial Communities: Implications for Nutrient Cycling in Soil

BackgroundMany microorganisms have a wide temperature growth range and versatility to tolerate large thermal fluctuations in diverse environments, however not many have been fully explored over their entire growth temperature range through a holistic view of its physiology, genome, and transcriptome. We used Exiguobacterium sibiricum strain 255-15, a psychrotrophic bacterium from 3 million year old Siberian permafrost that grows from -5°C to 39°C to study its thermal adaptation.ResultsThe E. sibiricum genome has one chromosome and two small plasmids with a total of 3,015 protein-encoding genes (CDS), and a GC content of 47.7%. The genome and transcriptome analysis along with the organisms known physiology was used to better understand its thermal adaptation. A total of 27%, 3.2%, and 5.2% of E. sibiricum CDS spotted on the DNA microarray detected differentially expressed genes in cells grown at -2.5°C, 10°C, and 39°C, respectively, when compared to cells grown at 28°C. The hypothetical and unknown genes represented 10.6%, 0.89%, and 2.3% of the CDS differentially expressed when grown at -2.5°C, 10°C, and 39°C versus 28°C, respectively.ConclusionThe results show that E. sibiricum is constitutively adapted to cold temperatures stressful to mesophiles since little differential gene expression was observed between 4°C and 28°C, but at the extremities of its Arrhenius growth profile, namely -2.5°C and 39°C, several physiological and metabolic adaptations associated with stress responses were observed.

Characterization of Exiguobacterium isolates from the Siberian permafrost. Description of Exiguobacterium sibiricum sp. nov.

Culture-dependent and -independent methods were employed to determine the impact of carboxyl-functionalized single-walled carbon nanotubes (SWNTs) on fungal and bacterial soil microbial communities. Soil samples were exposed to 0 (control), 250, and 500 μg of SWNTs per gram of soil. Aliquots of soil were sampled for up to 14 days for culture-dependent analyses, namely, plate count agar and bacterial community level physiological profiles, and culture-independent analyses, namely, quantitative real-time polymerase chain reaction (qPCR), mutliplex-terminal restriction fragment length polymorphism (M-TRFLP), and clone libraries. Results from culture-independent and -dependent methods show that the bacterial soil community is transiently affected by the presence of SWNTs. The major impact of SWNTs on bacterial community was observed after 3 days of exposure, but the bacterial community completely recovered after 14 days. However, no recovery of the fungal community was observed for the duration of the experiment. Physiological and DNA microbial community analyses suggest that fungi and bacteria involved in carbon and phosphorus biogeochemical cycles can be adversely affected by the presence of SWNTs. This study suggests that high concentrations of SWNTs can have widely varying effects on microbial communities and biogeochemical cycling of nutrients in soils.