Identification and characterization of nematicidal activity of organic volatiles from a Pseudomonad rhizobacterium

Plant parasitic nematodes (PPNs) cause huge agricultural and silvicultural losses every year. Most studies that investigated various mechanisms for killing nematodes used the model organism Caenorhabditis elegans. Pseudomonas chlororaphis is an important biocontrol bacterium with great application potential in agriculture. Pseudomonas chlororaphis strains have the potential to control PPNs. In our previous study, we obtained one P. chlororaphis-like bacterium, namely, SPS-41, from the rhizosphere of sweet potato. This strain exhibited wide-spectrum of antifungal activity. In the present study, the nematicidal activity of the P. chlororaphis SPS-41 strain against C. elegans was examined. This strain was identified as Pseudomonas chlororaphis subsp. aureofaciens via 16S rRNA phylogenetic analysis. Results showed that this strain could kill nematodes in a short time on both fast- and slow-media. Both the liquid culture and volatile organic compounds (VOCs) produced by this strain exhibited strong nematicidal activity. VOCs fumigation by the SPS-41 strain triggered the immune response of C. elegans. A total of 23 VOCs from this strain were analyzed via solid-phase microextraction gas chromatography–mass spectrometry. Seven major VOCs were picked to test its nematicidal activity. Four of these VOCs, namely, 2-methyl-1-butanol, octanoic acid ethyl ester, ethyl acetate, and isobutyl acetate, could kill nematodes. Octanoic acid ethyl ester displayed the strongest nematocidal activity. The results suggested that the SPS-41 strain and its VOCs can be used as a new strategy for controlling nematodes.