Bacterial community assemblages in the rhizosphere soil, root endosphere and cyst of soybean cyst nematode-suppressive soil challenged with nematodes

In disease-suppressive soil, plants rely upon mutualistic associations between roots and specific microbes for nutrient acquisition and disease suppression. Notably, the transmission of suppressiveness by the cysts of sugar beet cyst nematode from suppressive to conducive soils has been previously observed in greenhouse trials. However, our current understanding of the bacterial assemblages in the cyst, root endosphere and rhizosphere soil is still limited. To obtain insights into these bacterial microbiota assemblages, the bacterial communities inhabiting the plant-associated microhabitats and cysts in soybean cyst nematode (SCN)-suppressive soil were characterized by deep sequencing, using soybean grown under growth room conditions with additional SCN challenge. Clustering analysis revealed that the cyst bacterial community was closer to the root endosphere community than to the rhizosphere and bulk soil communities. Interestingly, the cyst bacterial community was initially established by the consecutive selection of bacterial taxa from the soybean root endosphere. We found a set of potential microbial consortia, such as Pasteuria, Pseudomonas, Rhizobium, and other taxa, that were consistently enriched in the rhizocompartments under SCN challenge, and more abundant in the cysts than in the bulk soil. Our results suggest that the soybean root-associated and cyst microbiota may cause the suppressiveness of SCN in suppressive soil.