State Key Laboratory of Mycology, Institute of Microbiology, Chinese Academy of Sciences, Beijing, 100101, China.
University of Chinese Academy of Sciences, Beijing, 100049, China.
Microbiome. 2024 Jul 15;12(1):125. doi: 10.1186/s40168-024-01840-x.
Soybean cyst nematodes (SCN) as animal parasites of plants are not usually interested in killing the host but are rather focused on completing their life cycle to increase population, resulting in substantial yield losses. Remarkably, some agricultural soils after long-term crop monoculture show a significant decline in SCN densities and suppress disease in a sustainable and viable manner. However, relatively little is known about the microbes and mechanisms operating against SCN in such disease-suppressive soils.
Greenhouse experiments showed that suppressive soils (S) collected from two provinces of China and transplantation soils (CS, created by mixing 10% S with 90% conducive soils) suppressed SCN. However, SCN suppressiveness was partially lost or completely abolished when S soils were treated with heat (80 °C) and formalin. Bacterial community analysis revealed that the specific suppression in S and CS was mainly associated with the bacterial phylum Bacteroidetes, specifically due to the enrichment of Chitinophaga spp. and Dyadobacter sp., in the cysts. SCN cysts colonized by Chitinophaga spp. showed dramatically reduced egg hatching, with unrecognizable internal body organization of juveniles inside the eggshell due to chitinase activity. Whereas, Dyadobacter sp. cells attached to the surface coat of J2s increased soybean resistance against SCN by triggering the expression of defence-associated genes. The disease-suppressive potential of these bacteria was validated by inoculating them into conducive soil. The Dyadobacter strain alone or in combination with Chitinophaga strains significantly decreased egg densities after one growing cycle of soybeans. In contrast, Chitinophaga strains alone required more than one growing cycle to significantly reduce SCN egg hatching and population density.
This study revealed how soybean monoculture for decades induced microbiota homeostasis, leading to the formation of SCN-suppressive soil. The high relative abundance of antagonistic bacteria in the cyst suppressed the SCN population both directly and indirectly. Because uncontrolled proliferation will likely lead to quick demise due to host population collapse, obligate parasites like SCN may have evolved to modulate virulence/proliferation to balance these conflicting needs. Video Abstract.
作为植物寄生虫的大豆胞囊线虫（SCN）通常对杀死宿主不感兴趣，而是专注于完成其生命周期以增加种群数量，从而导致大量减产。值得注意的是，一些长期种植单一作物的农业土壤中的 SCN 密度会显著下降，并以可持续和可行的方式抑制病害。然而，对于这种具有疾病抑制作用的土壤中针对 SCN 的微生物和机制，我们知之甚少。
温室实验表明，从中国两个省份采集的抑制性土壤（S）和移植土壤（CS，通过将 10%S 与 90%有利土壤混合制成）抑制了 SCN。然而，当 S 土壤经过热处理（80°C）和福尔马林处理时，SCN 的抑制作用部分丧失或完全丧失。细菌群落分析表明，S 和 CS 中的特异性抑制主要与细菌门拟杆菌门有关，特别是由于噬几丁质菌属和二型菌属在胞囊中的富集。噬几丁质菌属定殖的 SCN 胞囊孵化率显著降低，由于几丁质酶活性，卵壳内幼虫的内部体组织无法识别。而附着在 J2 表面的二型菌属细胞通过触发防御相关基因的表达增加了大豆对 SCN 的抗性。通过将这些细菌接种到有利土壤中，验证了它们的疾病抑制潜力。单独的二型菌属或与噬几丁质菌属联合显著降低了大豆一个生长周期后的卵密度。相比之下，噬几丁质菌属单独需要超过一个生长周期才能显著降低 SCN 卵孵化和种群密度。
本研究揭示了大豆连续几十年的单一栽培如何诱导微生物组稳态，导致 SCN 抑制性土壤的形成。在胞囊中具有拮抗作用的高相对丰度的细菌直接和间接抑制了 SCN 种群。由于不受控制的增殖可能会由于宿主种群崩溃而迅速消亡，因此像 SCN 这样的专性寄生虫可能已经进化出调节毒力/增殖的能力，以平衡这些相互冲突的需求。
