Phase-Specific Yeast Growth Responses to an Atmospheric-Pressure Plasma Jet Under Direct and Plasma-Activated Medium Conditions

We investigated the effects of atmospheric-pressure plasma treatment on the growth of Saccharomyces cerevisiae by directly comparing plasma exposure and plasma-activated medium (PAM) under strictly identical discharge conditions. An atmospheric-pressure plasma jet operated with argon (Ar) or nitrogen (N₂) was used. Yeast growth was analyzed using a phase-resolved kinetic framework that separately evaluated early growth behavior and exponential growth rate based on optical density measurements. Growth curves were normalized to same-day untreated controls to minimize day-to-day variability. Under N₂ plasma conditions, both direct exposure and PAM treatment resulted in limited changes in growth kinetics (μ_rel = 0.67–0.97; t_rel ≈ 1.02–1.09). In contrast, Ar plasma treatment produced clear mode-dependent effects. Direct exposure delayed growth initiation (t_rel = 1.00–1.40) with a moderate reduction in μ_rel (0.63–0.84). PAM treatment strongly suppressed μ_rel (0.19–0.50), whereas t_rel varied across conditions without systematic prolongation (0.59–1.09). These findings demonstrate that treatment mode strongly influences which growth phase is predominantly affected, highlighting the importance of phase-resolved kinetic analysis for distinguishing plasma-induced biological effects beyond conventional endpoint measurements.