Date Published: September 27, 2018
Publisher: Public Library of Science
Author(s): Yumiko F. Saito, Saki H. Miyazaki, Derek G. Bartlem, Yukiko Nagamatsu, Tamao Saito, Mette Vestergård.
Slime mold species in the genus Dictyostelium are considered to have a close relationship with non-parasitic nematodes; they are sympatric in soils and can exhibit interspecific competition for food. We investigated whether this relationship extends to a plant-parasitic nematode that is active in the rhizosphere and has broad host specificity, damaging crops worldwide. Using a novel assay to examine the interaction between the cellular slime mold, Dictyostelium discoideum, and the plant-parasitic nematodes, Meloidogyne spp., we found that cellular slime molds can repel plant parasitic nematodes. Specifically, the repulsion activity was in response to chemical compounds released by cellular slime mold fruiting bodies. Under laboratory conditions, these soluble chemical extracts from fruiting bodies of D. discoideum showed repulsion activity strong enough to protect plant roots. The fruiting body cell extracts repelled but were not toxic to the plant-parasitic nematodes.
Cellular slime mold species in the genus Dictyostelium are soil microbes that feed on bacteria and yeasts. These cellular slime molds have a unique two-stage life cycle, including a uni-cellular and a multi-cellular stage. While consuming bacteria or yeasts in the soil, Dictyostelium spp. live as uni-cellular amoebae and increase in abundance via binary fission (vegetative-stage). Upon starvation, amoebic cells aggregate and transform into intermixed multi-cellular mounds, referred to as slugs, that differentiate into anterior prestalk and posterior prespore cells at random positions in the mound . Using phototaxis and thermotaxis, slugs move toward the surface of the soil and complete cellular differentiation into the fruiting body, which form a spore head consisting of a mass of stress-resistant spores. Recently, more attention has been given to ecological studies of Dictyostelium species. There are several reports describing the interaction between slime mold species and bacteria [2–4]. The chemical compounds released from bacteria were identified as a predator defense mechanism [5–7].
Kessin et al. (1996) suggested that there was a predator–prey relationship between cellular slime mold species in the genus Dictyostelium and the free-living nematode, Caenorhabditis elegans . Due to the large number of potential secondary metabolites produced by D. discoideum [17,18] and that the soil can be considered a battle field of chemical warfare between microorganisms, we were interested in the chemical ecology of cellular slime molds and nematodes. We focused on the relationship between D. discoideum and the plant-parasitic root-knot nematode, M. incognita, that damages crops worldwide.
Our findings indicate that parasitic nematodes and cellular slime molds exhibit an interspecific chemical communication. The chemical compounds released from the fruiting bodies of D. discoideum were active against plant-parasitic nematodes and protected plants from infection. Our results reveal an exciting and novel avenue for management of nematode crop pests.