Nematodes avoid and are killed by Bacillus mycoides-produced styrene.

Root-knot nematodes are obligate parasites that feed on plant roots and cause serious crop losses worldwide. Bacillus species (Bacilliaceae) can produce nematicidal metabolites and have shown good potential for biological control of nematodes. In this study, Bacillus mycoides strain R2 isolated from rhizosphere soil of tomato plants exhibited high nematicidal activity against the free-living nematode Caenorhabditis elegans and the root-knot nematode Meloidogyne incognita. In a pot experiment, control efficiency of B. mycoides R2 on M. incognita was as high as 90.94%. The nematicidal compound was isolated and identified as styrene. The median lethal concentration of styrene against M. incognita was 4.55 μg/ml (m/v). The volatile styrene caused avoidance and killed nematodes primarily by the olfactory neuron and G protein signal pathway. C. elegans detected styrene with the AWB neuron; the signal was then transmitted to the downstream G protein coupled receptors CHE-3, DOP-3, and STR-2. Then signal activated G protein GPA-3 and GPA-7. The signal was then transmitted to ion channels (CNGs channel and TRPV channel), causing calcium ion internal flow and a stress response towards the increased concentration of intracellular calcium. Styrene should be registered as a nematode repellent and biocontrol agent for protection of crops against root-knot nematode attack.