Characterization of the volatilome of Lysobacter capsici AZ78 and its bioactivity against soilborne plant pathogenic fungi and oomycetes

Recently, it has been shown that volatile organic compounds (VOCs) produced by soil bacterium L. capsici DSM 19286 were highly active against Phytophthora infestans in vitro, when the strain was grown in a protein rich medium [1]. In contrast, the VOC-mediated inhibitory effect was attenuated when the strain was grown in a sugar rich medium. Based on these findings, we studied the effect of medium composition on the inhibition activity of L. capsici AZ78 against plant pathogens (e.g. Rhizoctonia solani). In parallel, GC-MS was combined with dynamic headspace (DHS) extraction and thermodesorption to investigate both type and relative amount of VOCs produced by the bacterium grown in media with crescent sugar (glucose) concentrations. Generally, the emission profiles differed in the relative amount and not in the type of VOCs produced. The chemical group of pyrazines was the most abundant in the volatile profile of L. capsici AZ78 growing in the various media. We additionally conducted experiments using a setup with Petri dishes having two compartments, where we measured the VOCs profile in the one compartment when the bacterium was growing on crescent sugar concentrations in the other. We confirmed the presence of the identified VOCs, thus giving an insight into which compounds may contribute to L. capsici AZ78 bioactivity, exhibited during the pathogen inhibition assay. Currently, we are examining the inhibitory effects of the identified compounds against various plant pathogens in vitro, with the aim to understand the mechanisms of VOC-mediated microbe-microbe communications and to select bioactive VOCs for the further development of novel biopesticides.