## 1 Introduction  
Fungi are eukaryotic organisms that grow with hyphal cells and produce spores. They have evolved diverse morphological and genetic groups that are estimated to include 1.5-5.0 million species on earth [1]. They play key roles in natural ecosystems as material decomposers, mutualists with other organisms, and pathogens of animals, plants, and humans [2]. As plant pathogens, their increased infection on agricultural crops has been threatening food security worldwide [3]. Furthermore, the increase and broadening of their infection on wild host species have brought about severe die-offs and extinctions in some species [4]. As human pathogens, fungi can infect different parts of the human body such as lung, skin, and brain [5, 6]. Infections of the membranes surrounding the spinal cord and brain and blood stream are less common than skin and lung infections but can be detrimental and fatal. Invasive pathogenic fungi can cause disease in healthy people and opportunistic fungal pathogens infect individuals already experiencing severe illness. Many fungi form small round airborne dispersal spores, which are produced from hyphal cells. Fungal spores dispersed through the air can adhere to medical devices and the surface of vegetables and fruits during food processing. Thus, fungal spores found in both indoor and outdoor environments have an infective potential in personal and public health and a contamination potential in food spoilage [7; 8]. The management of fungal spores has been essential in the medical and food industry for the protection of human health and control of food hygiene. Diverse approaches including biological, chemical, and physical methods such as antifungal agents, photodynamic therapy, ultra-violet (UV) light sterilizer, and plasma treatment have been applied for fungal spore inactivation [9; 10; 11]. However, the application of each method has merits and demerits. Recently, the effects of nonthermal atmospheric pressure plasma jets (NTAPPJ) on fungi have attracted considerable attention. An atmospheric pressure plasma jet or dielectric barrier discharge (DBD) plasma has been used for sterilization, inactivation, and cancer treatment [11; 12; 13; 14; 15; 16; 17; 18; 19]. We have been working on the effects of plasma treatment on the viability of fungal spores as a plasma sterilizer for fungal pathogens [19; 20; 21; 22]. The atmospheric pressure plasma jet was applied to two entomopathogenic fungal species, and the results showed that it has the potential to be developed as an antifungal device. In a previous study exploring the killing mechanism of fungal spores by plasma treatment, it was demonstrated that plasma has a direct impact on the fungal cell wall and cellular components such as nucleolus DNA [19; 20; 21; 22]. Generally, NTAPPJ could generate reactive oxygen and nitrogen species (RONS). When interacting with an aqua medium, NTAPPJ can produce additional reactive species by reactions between plasma radicals and water molecules, which could also be detrimental to fungal spores. NTAPPJ-treated water is known simply as plasma-activated water (PAW). The inactivation efficacy of PAW on fungal spores and biofilms was recently reported in _Aspergillus flavus_, a food contaminant [23]. However, how the PAW contributes to the damage of fungal spores, especially dark melanized and environmentally resistant spores, is not clear. Understanding of the mechanism of fungal spore inactivation by PAW is of great interest because PAW makes it possible to kill fungi in a relatively large volume that cannot be achieved by plasma jet. This study was performed to clarify the influence of PAW on the viability and cell wall integrity of melanized fungal spores. For this purpose, we selected _Aspergillus brasiliensis_ (formerly _A. niger_), a fungal species that produces tremendous amounts of melanin pigmented spores within short time periods and is present in the air and our living environment [24]. _A. brasiliensis_ is a member of the black aspergillus including _A. aculeatus_, _A.