土传病原细菌的生存与致病权衡

土传病原细菌严重威胁土壤-植物系统健康和农业可持续发展。在接触和入侵寄主植物根系之前，病原细菌会经受土壤pH、含氧量、营养物质种类和数量等非生物因素骤变以及其他土壤微生物的竞争、寄生和捕食等生物胁迫。病原细菌的生物膜形成、代谢、运动、毒力、DNA修复以及对噬菌体、抗生素或环境压力的抵抗能力等特性对其在土壤环境中生存和侵染寄主非常重要。为适应复杂且多变的土壤生物和非生物环境，病原细菌必须动态权衡其生存和致病力之间的关系，维持其生存、传播、增殖和侵染致病间的平衡，以最大化其在土壤环境中的适应性。系统理解土传病原细菌应对胁迫和侵染寄主植物的过程及权衡机制是建立精准、高效生态防控手段的关键。为此，以土传病原细菌为代表，总结了土传病原细菌生存与致病的权衡规律和典型现象及土壤中的生物和非生物影响因素，阐述了土传病原细菌入侵植物根际过程中的生存与致病权衡机制，并提出一些与土传病原细菌生存与致病权衡相关的科学问题，呼吁建立基于生存-致病权衡理论的土传病害生态防控策略，为绿色农业可持续发展提供理论参考。

Survival-virulence Trade-off of Soil-borne Pathogenic Bacteria

Soil-borne pathogenic bacteria threaten health of the soil-plant system and sustainable development of the agriculture. The soil ecosystem is complicated with tangled interactions of abiotic and biotic factors. Before contacting and invading the host plant root system, pathogenic bacteria often encounter sudden changes in abiotic factors, such as pH, oxygen content and types and contents of nutrients or biotic stresses, like competition, parasitism and predation of other soil microorganisms. Pathogenic bacteria have numerous capabilities, like biofilm formation, metabolism, movement, virulence, DNA repair, and resistance to bacteriophages, antibiotics, and other environmental stresses, which are essential for them to survive in the soil and infect host plants. To adapt to the complicated and variable soil biotic and abiotic environment, pathogenic bacteria have to trade off dynamically between survival and virulence so as to maintain the balance between survival, spread, proliferation and infection in soil and to maximize their adaptability in the soil environment. A systematic understanding of the processes and mechanisms of the survival-virulence trade-off of soil-borne pathogenic bacteria is the key to establishing efficient and precise ecological prevention and control strategies. To this end, this review first introduces the trade-off theory and survival-virulence trade-off of soil-borne pathogenic bacteria. Soil-borne pathogenic bacteria allocate more resources either on survival or virulence for adaption to for adaption to the environment. It is costly for pathogenic bacteria to resist stresses while producing virulent secretions. They have to reduce the production of virulent secretions to achieve the ability to resist stresses. Viable but non-cultivable status and phenotypic conversion are two typical phenomena of the survival-virulence trade-off in soil borne pathogenic bacteria to optimize the balance of viability and pathogenicity. In the second section, this paper elaborates on how abiotic and biotic factors influencing the survival-virulence trade-off of the pathogenic bacteria in the soil environment. Soil is a complex and constantly changing living habitat for bacteria, containing various stressful factors to threaten the existence of pathogenic bacteria. Harsh environmental factors can trigger resistant systems in the bacteria, which is rather costly, thus leading to a cut-down investment in the expression of virulent features. So this paper analyzed and summarized those phenomena from the perspective of mechanism. In the third section, this paper focused on this trade-off pattern in the process of pathogenic bacteria moving from bulk soil to root surface: migration from soil to rhizosphere, colonization and proliferation in rhizosphere and invasion to root surface, since the infection of host plants is a continuous and dynamic process varying temporally and spatially. The last section of this paper proposed several research topics relative to the survival-virulence trade-off theory: 1) explore impacts of biotic and abiotic factors on survival and virulence characteristics of pathogenic bacteria; 2) enhance the understanding of the multi-level interactions in the rhizosphere micro-food web and the superimposition of biotic and abiotic factors on the survival-virulence trade-off in soil-borne pathogenic bacteria; 3) investigate the molecular mechanism of adaptive evolution of pathogenic bacteria. This paper calls for establishment of an ecological prevention and control strategy for soil-borne diseases based on the survival-virulence trade-off theory. Moreover, it is expected that this paper may provide certain theoretical reference for sustainable development of the green agriculture.