Sonoplasma treatment of drinking water reduces yeast culturability both immediately and progressively during holding

Sonoplasma treatment (SPT) combines hydrodynamic cavitation with electrical discharge, generating reactive oxygen species (ROS) and local mechanical stress in water. In this study, six yeast species (Candida albicans, C. parapsilosis, C. tropicalis, Naganishia albida, Rhodotorula mucilaginosa, and Tausonia pullulans) were used as eukaryotic model organisms to assess SPT efficacy in drinking water and to distinguish immediate from delayed ("treat-and-hold") effects. Standardized suspensions (1.0-1.1 McFarland) were inoculated into 9 L of drinking water and processed at 30 kHz using 1-10 consecutive SPT cycles. Hydrogen peroxide accumulated approximately linearly with cycle number (slope ≈ 0.85 mmol L⁻¹ per cycle, R² = 0.995). At 1 h after treatment, culturability was last detected at cycle 2 for C. albicans, cycle 7 for C. tropicalis, and cycle 9 for R. mucilaginosa, while C. parapsilosis, N. albida, and T. pullulans remained detectable after 10 cycles. During holding after 1-2 cycles, all species underwent progressive post-treatment loss of culturability compared to time-matched controls, with the last detectable time point ranging from 1 h (C. albicans, C. tropicalis) to day 5 (C. parapsilosis, N. albida) after a single cycle; all tested species became non-detectable within the 10-day observation window. These observations indicate that immediate tolerance to SPT varied among the yeasts tested, while loss of culturability during holding was consistent across species, supporting the use of yeasts as stringent eukaryotic benchmarks for plasma-activated water (PAW)-based hybrid disinfection.