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.

RESUMOOs efluentes têxteis liberam grandes quantidades de resíduos de corantes no meio ambiente, poluindo e alterando todo o ecossistema aquático. Além da poluição visual os compostos possuem alta toxicidade, quando não tratado corretamente podem gerar bioacumulação na biota. A levedura Saccharomyces cerevisiae, comumente utilizada como biocatalizador nas indústrias, é um possível adsorvente, devido à estrutura química composta pela parede celular, contendo grupos amino sítio ativo de possíveis interações com os grupamentos sulfônicos pertencentes aos corantes reativos, cuja comercialização compreende em escala mundial. Para tanto, foi realizado um estudo de remoção do corante reativo Direct Orange 2GL pelo método de adsorção, utilizando analises em espectrofotômetro de UV-Vis, mediante a diferentes concentrações de biomassa de S. cerevisiae e valores de pH em solução. O experimento foi analisado a partir do gráfico de isotermas de adsorção, visando à capacidade máxima de adsorção do corante na parede celular da levedura a partir do tratamento matemático usando como modelo as equações de Langmuir e Freundlich e suas linearizações. Os experimentos ressaltaram os possíveis mecanismos de interações químicas, entre adsorbato/adsorvente, podendo apresentar formação em monocamadas ou multicamadas a partir do coeficiente de correlação relativo mediante a influência do valor de pH. As analises em espectrofotômetro UV-Vis, exibiram eficiência no decrés-cimo dos valores de absorvância em relação ao valor no pico de onda máximo, com resultados de 0,063 absorvância, sendo este um valor aceitável para o padrão de absorvância permitido no descarte de corante. Desse modo, a utilização de biomassa de S. cerevisiae propicia resultados relevantes mesmo a baixas concentrações desde que ajustado os valores de pH em solução.Palavras-chave: adsorção, corante têxtil, levedura. ABSTRACTThe textile effluents release large amounts of dye waste in the environment, polluting and altering the whole aquatic ecosystem. Besides the visual pollution compounds have high toxicity, if not treated properly can generate bioaccumulation in biota. The yeast Saccharomyces cerevisiae, commonly used as a biocatalyst in industries is a possible adsorbent due to the chemical structure composed of the cell wall containing amino groups, active site location of possible interactions with sulfonic groups belonging to reactive dyes, which marketing worldwide. This way, it was performed to removal study of reactive dye Direct Orange 2GL by adsorption method using a spectrophotometer analysis of UV-Vis to the different biomass concentrations of S.

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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. The study characterized ZnO NPs using X-ray diffraction, FT-IR spectroscopy and scanning electron microscopy. Antimicrobial activity of clinically bacteria Escherichia coli, Staphylococcus aureus, Bacillus subtilis and Pseudomonas aeruginosa was evaluated by REMA after exposure to the ZnO NP at concentrations from 0.2 to 1.4 mM. Sensitivity was achieved at 0.6 mM for the Gram-negatives and 1.0 mM for Gram-positives cells. The effect of ZnO NPs on the membrane integrity and in the interference of cell division was investigated by its effect on the divisional ring, through fluorescence microscopy assays using B. subtilis (amy::pspac-ftsZ-gfpmut1) expressing FtsZ-GFP. Results showed that ZnO NPs did not interfere with the assembly of the divisional Z-ring. However, 70% of the cells showed damage in the cytoplasmic membrane after 15 min of exposure to the ZnO NPs. Electrostatic forces, production of Zn2+ ions, generation of reactive oxygen species were described as pathways of bactericidal action by ZnO. Thus, understanding bactericidal MOA can produce predictive models to prevent bacterial resistance and lead to further research.

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