Enhancement of yeast proliferation using atmospheric pressure pulsed discharge plasmas

Here, we demonstrate the enhancement of the yeast proliferation by exposing to pulsed power driven atmospheric pressure plasmas (APP). A magnetic pulse compressor delivers positive high voltage pulses repetitively to a multi-needle electrode, which were set in a transparency plastic vessel with a gas flow. Yeast, Saccharomyces cerevisiae, was put on agar in a metal laboratory dish, which was directly placed on the plane electrode. The distance between the multi-needle electrode and agar was 5 mm. A pulse width and a repetition frequency of the voltage pulse were 100 ns and 100 Hz, respectively. The widely spreading plasmas to the agar surface were produced when helium gas was mixed and the voltage pulses exceeding 5 kV were delivered. Proliferation activity of the yeast was evaluated by a growth rate of the colony size on agar. Emission and absorption spectroscopies were conducted to detect reactive species in the plasma and its surrounding area. The proliferation clearly depends on the exposure time to the APP. The proliferation was enhanced in the case of the exposure time less than 20 s, whereas yeast was killed by the exposure more than 20 s. According to the spectroscopies, ozone, nitrogen oxide and hydroxyl radicals may play important roles to activate and inactivate yeast.