Zinc oxide nanoparticles (ZnO NPs) are one of the most widely used nanoparticulate materials due to their antimicrobial properties, but their main mechanism of action (MOA) has not been fully elucidated. This study characterized ZnO NPs by using X-ray diffraction, FT-IR spectroscopy and scanning electron microscopy. Antimicrobial activity of ZnO NPs against the clinically relevant bacteria Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and the Gram-positive model Bacillus subtilis was evaluated by performing resazurin microtiter assay (REMA) after exposure to the ZnO NPs at concentrations ranging from 0.2 to 1.4 mM. Sensitivity was observed at 0.6 mM for the Gram-negative and 1.0 mM for the Gram-positive cells. Fluorescence microscopy was used to examine the interference of ZnO NPs on the membrane and the cell division apparatus of B. subtilis (amy::pspac-ftsZ-gfpmut1) expressing FtsZ-GFP. The results showed that ZnO NPs did not interfere with the assembly of the divisional Z-ring. However, 70% of the cells exhibited damage in the cytoplasmic membrane after 15 min of exposure to the ZnO NPs. Electrostatic forces, production of Zn2+ ions and the generation of reactive oxygen species were described as possible pathways of the bactericidal action of ZnO. Therefore, understanding the bactericidal MOA of ZnO NPs can potentially help in the construction of predictive models to fight bacterial resistance.

Curcumin is the main constituent of turmeric, a seasoning popularized around the world with Indian cuisine. Among the benefits attributed to curcumin are anti-inflammatory, antimicrobial, antitumoral, and chemopreventive effects. Besides, curcumin inhibits the growth of the gram-positive bacterium Bacillus subtilis. The anti-B. subtilis action happens by interference with the division protein FtsZ, an ancestral tubulin widespread in Bacteria. FtsZ forms protofilaments in a GTP-dependent manner, with the concomitant recruitment of essential factors to operate cell division. By stimulating the GTPase activity of FtsZ, curcumin destabilizes its function. Recently, curcumin was shown to promote membrane permeabilization in B. subtilis. Here, we used molecular simplification to dissect the functionalities of curcumin. A simplified form, in which a monocarbonyl group substituted the β-diketone moiety, showed antibacterial action against gram-positive and gram-negative bacteria of clinical interest. The simplified curcumin also disrupted the divisional septum of B. subtilis; however, subsequent biochemical analysis did not support a direct action on FtsZ. Our results suggest that the simplified curcumin exerted its function mainly through membrane permeabilization, with disruption of the membrane potential necessary for FtsZ intra-cellular localization. Finally, we show here experimental evidence for the requirement of the β-diketone group of curcumin for its interaction with FtsZ.

The use of synthetic dyes is commonplace in many industries, and the effluent is often dumped into the environment with no prior treatment. The aim of the present study was to analyze the use of an industrial strain of Saccharomyces cerevisiae (Meyen) for the removal of the textile dye Acid Blue 161 from an aqueous solution. Kinetic, isotherm, and thermodynamic models were created to evaluate the biosorption mechanisms. Fourier transfer infrared (FT-IR) spectroscopy was used to characterize and identify possible binding sites. A toxicity test was also performed using Artemia salina to analyze the degree of toxicity of the dye following treatment. The kinetic results demonstrated the occurrence of intraparticle diffusion in the yeast cells as the controlling mechanism of the sorption process. Biosorption followed the Langmuir model, except at pH 8.50, when it fit the Freundlich model. The thermodynamic results demonstrate that the biosorption process is spontaneous and endothermic. The FT-IR analyses confirmed the occurrence of a chemical reaction in acid pH, but physical adsorption only occurred at pH 8.50. The toxicity test showed that the use of the yeast biomass led to the complete removal of toxicity from the dye solution, demonstrating the effectiveness of the biosorption process in the treatment of effluents contaminated with these compounds.

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A versatile peptide‐based toolbox for surface functionalization was established by a combination of a universal material binding peptide (LCI‐anchor peptide) and sortase‐mediated bioconjugation (sortagging). This toolbox facilitates surface functionalization either as a one‐ or a two‐step strategy. In the case of the one‐step strategy, the desired functionality was directly introduced to LCI. For the two‐step strategy, LCI was modified with a reactive group, which can be further functionalized (e.g., employing “click” chemistry). Sortagging of LCI, employing sortase A from Staphylococcus aureus, was achieved with six different amine compounds: dibenzocyclooctyne amine, biotin‐polyethylene glycol amine, Cyanine‐3 amine, kanamycin, methoxypolyethylene glycol amine (Mn = 5000 Da), and 2,2,3,3,4,4,4‐Heptafluorobutylamine. The purification of LCI‐amine sortagging products was performed by a negative purification using Strep‐tag II affinity chromatography, resulting in LCI‐amine conjugates with purities >90%. For the two‐step strategy, the LCI‐dibenzocyclooctyne sortagging product was purified and enabled, through copper‐free azide–alkyne “click” chemistry, universal surface functionalization of material surfaces such as polypropylene, polyethylene terephthalate, stainless steel, gold, and silicon. The click reaction was performed before or after surface binding of LCI‐dibenzocyclooctyne. Finally, in the case of the one‐step strategy, polypropylene was directly functionalized with Cyanine‐3 and biotin‐polyethylene glycol amine.

Isobavachalcone (IBC) is a natural prenylated chalcone with a broad spectrum of pharmacological properties. In this work, we newly synthesized and investigated the antibacterial activity of IBC against Gram-positive, Gram-negative and mycobacterial species. IBC was active against Gram-positive bacteria, mainly against Methicillin-Susceptible Staphylococcus aureus (MSSA) and Methicillin-Resistant Staphylococcus aureus (MRSA), with minimum inhibitory concentration (MIC) values of 1.56 and 3.12 µg/mL, respectively. On the other hand, IBC was not able to act against Gram-negative species (MIC > 400 µg/mL). IBC displayed activity against mycobacterial species (MIC = 64 µg/mL), including Mycobacterium tuberculosis, Mycobacterium avium and Mycobacterium kansasii. IBC was able to inhibit more than 50% of MSSA and MRSA biofilm formation at 0.78 µg/mL. Its antibiofilm activity was similar to vancomycin, which was active at 0.74 µg/mL. In order to study the mechanism of the action by fluorescence microscopy, the propidium iodide (PI) and SYTO9 fluorophores indicated that IBC disrupted the membrane of Bacillus subtilis. Toxicity assays using human keratinocytes (HaCaT cell line) showed that IBC did not have the capacity to reduce the cell viability. These results suggested that IBC is a promising antibacterial agent with an elucidated mode of action and potential applications as an antibacterial drug and a medical device coating.

Waste from textile industries can severely harm the environment. Dyes are the main residues of these effluents. Saccharomyces cerevisiae is already known to be an efficient adsorbent for the removal of dyes. However, the lack of applicability and limitation of the use of cell biomass in an industrial treatment makes it impossible to apply them. Thus the aim of this work was to immobilize S. cerevisiae in cross-linked chitosan beads by two different techniques (contact immobilization and encapsulation in the polymer matrix), proposing two new materials for adsorption. Adsorption experiments were carried out to analyse the kinetics, isotherm and thermodynamics adsorptive of the synthesized materials. The adsorption data obtained were compared with the S. cerevisiae biomass and with the cell-free cross-linked chitosan beads to evaluate the efficiency of the two synthesized materials. The Fourier transform infrared spectrophotometer was used to characterize and analyse the main adsorption sites of the tested materials. Bioassays using the microcrustacean Daphnia similis verified if the materials could reduce the toxicity of the medium after its application in the treatment. Both materials synthesized in this work can potentially remove dyes from effluents, in addition to being able to significantly decrease dye toxicity from an aqueous medium.