Abstract
This research investigated the capture of nitrate by magnesium ions in plasma-activated water (PAW) and its antifungal effect on the cell viability of the newly emerged mushroom pathogen Cryptococcus pseudolongus. Optical emission spectra of the plasma jet exhibited several emission bands attributable to plasma-generated reactive oxygen and nitrogen species. The plasma was injected directly into deionized water (DW) with and without an immersed magnesium block. Plasma treatment of DW produced acidic PAW. However, plasma-activated magnesium water (PA-Mg-W) tended to be neutralized due to the reduction in plasma-generated hydrogen ions by electrons released from the zero-valent magnesium. Optical absorption and Raman spectra confirmed that nitrate ions were the dominant reactive species in the PAW and PA-Mg-W. Nitrate had a concentration-dependent antifungal effect on the tested fungal cells. We observed that the free nitrate content could be controlled to be lower in the PA-Mg-W than in the PAW due to the formation of nitrate salts by the magnesium ions. Although both the PAW and PA-Mg-W had antifungal effects on C. pseudolongus, their effectiveness differed, with cell viability higher in the PA-Mg-W than in the PAW. This study demonstrates that the antifungal effect of PAW could be manipulated using nitrate capture. The wide use of plasma therapy for problematic fungus control is challenging because fungi have rigid cell wall structures in different fungal groups.
Highlights
The effects of nonthermal atmospheric-pressure plasma on fungi, bacteria, and cancer cells have attracted considerable attention
Optical emission spectra of the plasma jet exhibited that reactive oxygen species (ROS) are dominant in the plasma plume at the end of the quartz tube, whereas reactive nitrogen species (RNS) are dominant at the end of the plume, as shown by optical emission spectroscopy (OES) and the NO2 distribution of the plasma jet
Mg water was treated with the plasma jet, the acidity of the plasma-activated magnesium water (PA-Mg-W) was weakened due to the reduction in the plasma-generated hydrogen ion by electrons released from the zerovalent magnesium (ZVM)
Summary
The effects of nonthermal atmospheric-pressure plasma on fungi, bacteria, and cancer cells have attracted considerable attention. No systematic study has performed the manipulation of nitrate ions in PAW generated using an atmospheric-pressure Ar plasma jet. This study was performed to examine the magnesium ion-induced nitrate capture in PAW and its antifungal effect on the Cryptococcus pseudolongus. To our knowledge, this is the first report in which PAW exhibits an antifungal effect on a Basidiomycota fungus. Mg water treated with a plasma jet (PAW and PA-Mg-W, respectively), and we studied the capture of nitrate in PAW by plasma-induced Mg2+ ions. We examined the effects of PAW and PA-Mg-W treatments on C. pseudolongus cells, and compared the viability of these PAW (PA-Mg-W)-treated cells with that of fungal cells treated by reference free nitrate (nitrate salt). We described variations in the viability of C. pseudolongus cells using the physicochemical properties of PAW and PA-Mg-W
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