Influence of Nonthermal Atmospheric Plasma-Activated Water on the Structural, Optical, and Biological Properties of Aspergillus brasiliensis Spores

Abstract

Plasma-activated water (PAW) has emerged as a platform for sterilizing fungal pathogens. In this study, we investigated the influence of PAW on black melanized spores of Aspergillus brasiliensis to explore the mechanism of fungal spore inactivation. PAW was prepared by activating deionized water with a nonthermal atmospheric pressure air plasma jet (soft plasma jet). The concentrations of H2O2 and NOx in the PAW treated by the soft plasma jet for 3 min were 50 μM and 1.8 mM, respectively, and the pH of the PAW was 3.10. The reactive oxygen and nitrogen species (RONS) in the PAW increased with longer plasma activation time. After being treated for 30 min in the PAW with a plasma activation time of 3 min, the spore viability dramatically dropped to 15%. The viabilities of 0.3% H2O2- and 0.3% HNO3-treated spores were 22% and 42%, respectively. The breakage of the spore cell wall by the PAW was revealed in scanning electron microscope images and flow cytometry measurements. Disruption of cell wall integrity provides a path for intracellular components to escape and RONS of the PAW can attack intracellular components directly. Degradation of high molecular genomic DNA was also observed by agarose gel electrophoresis. These results suggest that long-lived reactive species generated in the PAW play an important role in the inactivation of melanized fungal spores. Consequently, PAW produced by a soft plasma jet can be applied to sterilize bioprotective walled fungal spores in a relatively large volume.

The optimization of plasma activated water ( PAW ) generation and the inactivation mechanism of PAW on Escherichia coli

“…To evaluate the extent of species involvement in the microbial inactivation of PAW, Su et al (2018) demonstrated that • OH, • NO, and H 2 O 2 were the main species that changed morphology and destroyed and degraded the RNA and protein structure, causing virus inactivation. Moreover, Guo et al (2018) suggested that 1 O 2 was the main functional agent in PAW for bacteriophage inactivation, and Ki et al (2020) reported that the long‐lived reactive species in PAW had a good inactivation effect on melanized fungal spores. In our study, the results demonstrated that long‐lived species such as , were key players in bacterial inactivation, and the presented data gave evidence that was a significant contributor to antimicrobial activity of PAW.…”

Nitrate Capture Investigation in Plasma-Activated Water and Its Antifungal Effect on Cryptococcus pseudolongus Cells

“…As shown in Figure 5 d, the absorption spectra of the PAW and PA-Mg-W exhibited an absorption peak at 201 nm. As the reference nitrite and nitrate solutions have absorption peaks at 209 and 201 nm, respectively [ 12 , 46 ], the observed 201-nm absorption band indicates that nitrate ions greatly outnumber nitrite ions. Next, the nitrate absorption peak intensity at 300 nm was higher in the PA-Mg-W than in the PAW, as shown in Figure 5 a,b.…”

“…That is, Ascomycota fungi are characterized by gel-like α-1,3 glucans and galactomannoproteins, whereas Basidiomycota fungi are characterized by α-1,3 glucans along with xylomannoproteins [ 54 ]. In a previous work, we demonstrated that PAW influences the spore viability and cell wall integrity of the Ascomycota fungus, Aspergillus brasiliensis , which has melanized fungal spores [ 12 ]. We wondered whether PAW would be applicable to Basidiomycota fungi.…”

“…Therefore, PAW can also destroy the cells of Basidiomycota fungi encapsulated by a relatively thick cell wall. These results demonstrated that the PAW produced by the atmospheric-pressure Ar plasma jet is detrimental not only to Ascomycota fungal spores which were produced by conidiophores [ 12 ] but also to Basidiomycota yeast cells which were produced by budding. From the viewpoint of applications such as sanitary means, it is meaningful that the two taxonomically different major groups of fungi are susceptible enough to the PAW produced by the plasma jet.…”

“…Since the emergence of plasma medicine and plasma chemistry, PAW has attracted considerable interest for various applications in biological and medical science as well as in the water, agriculture, and food industries [ 1 , 2 ]. The mechanism of fungal spore inactivation by PAW is of particular interest because PAW can kill a larger volume of fungi than a direct plasma jet can [ 11 , 12 ]. To make PAW a practical tool, we need not only a fundamental understanding of its antifungal mechanism but also methods for handling the RONS in PAW in field applications.…”