Modulation of Arabidopsis thaliana growth by volatile substances emitted by Pseudomonas and Serratia strains

Many volatile compounds secreted by bacteria play an important role in the interactions of microorganisms, can inhibit the growth of phytopathogenic bacteria and fungi, can suppress or stimulate plant growth and serve as infochemicals presenting a new type of interspecies communication. In this work, we investigated the effect of total pools of volatile substances and individual volatile organic compounds (VOCs) synthesized by the rhizosphere bacteria Pseudomonas chlororaphis 449 and Serratia plymuthica IC1270, the soil-borne strain P. fluorescens B-4117 and the spoiled meat isolate S. proteamaculans 94 on Arabidopsis thaliana plants. We showed that total gas mixtures secreted by these strains during their growth on Luria-Bertani agar inhibited A. thaliana growth. Hydrogen cyanide synthesis was unnecessary for the growth suppression. A decrease in the inhibition level was observed for the strain P. chlororaphis 449 with a mutation in the gacS gene, while inactivation of the rpoS gene had no effect. Individual VOCs synthesized by these bacteria (1-indecene, ketones 2-nonanone, 2-heptanone, 2-undecanone, and dimethyl disulfide) inhibited the growth of plants or killed them. Older A. thaliana seedlings were more resistant to VOCs than younger seedlings. The results indicated that the ability of some volatiles emitted by the rhizosphere and soil bacteria to inhibit plant growth should be considered when assessing the potential of such bacteria for the biocontrol of plant diseases.