Activation of endophytic bacteria useful for plants by atmospheric plasma treatment

Abstract

The possibility of the activation of beneficial microorganisms using atmospheric plasma has rarely been examined. The application of plant growth-promoting bacteria (PGPB) as a microbial fertilizer to the field requires consistent efficiency. To overcome the limitations of PGPB as a microbial fertilizer, we investigated the potential of μ-dielectric barrier discharge plasma to increase the bacterial activity of a PGPB, Klebsiella pneumoniae, KW7-S06. Bacterial proliferation and vitality increased after plasma treatment. The infrared band of the observed Fourier transform infrared spectroscopy spectrum showed no change in the plasma-treated bacteria and untreated bacterial cell membranes. These results demonstrate that cells are not damaged by oxidative stress caused by plasma treatment. The density of bacteria adhering to the surface of rice seed inoculated with plasma-treated bacteria was higher than untreated bacteria. The germination rates of rice and barley seeds inoculated were significantly increased, and the growth of rice plants was also improved. The level of salicylic acid hormone was higher in rice plants infected with plasma-treated than with untreated bacteria. Our results demonstrated that plasma can accelerate bacterial growth and vitality, and the increased bacteria improved the adhesion of plant seed surfaces and elevated the level of phytohormones, leading to the enhancement of plant growth and tolerance to disease.