Bacterial wilt, caused by soil‐borne pathogen Ralstonia solanacearum, is a serious disease in many plants such as Solanaceae. To investigate the effects of accumulated nitrogen in soil on the phenotype and pathogenicity of the R. solanacearum, a serial passage experiment (SPE) was designed. Specifically speaking, minimal medium supplied with a slight excess of ammonium sulphate (AS) or ammonium nitrate (AN) was used to simulate the nutrition of soil containing excess nitrogen. During the period of 30 SPE, the phenotype, pathogenicity and relative expression of nitrogen metabolism genes in R. solanacearum were monitored. Phenotypic analysis results illustrated that the colony morphology of R. solanacearum changed after long‐term culture, from high virulence colonies with strong fluidity to small, round non‐mucoid colonies; The strain after prolonged stress of excessive exogenous nitrogen was a no‐virulence phenotype conversion type (PC‐type). The time for a change in colony morphology to occur after exposure to exogenous AS or AN was significantly less than the untreated samples, which treated without exogenous nitrogen. The results of pathogenicity also demonstrated that the cultures treated with exogenous AN or AS reduced virulence more quickly than the control. The disease index of 10 SPE with AN treatment or AS treatment was 89% or 68% lower than that of the control, respectively. In addition, as the incubation time increased, the swimming motility and the number of biofilms formation of the cultures were significantly changed under both treatments in comparison to the untreated samples. Furthermore, the relative expression of the nitric oxide reductase norB gene in the cultures treated with AN was 1.51‐fold higher compared with the control after 30 SPE. These results indicated that excessive nitrogen supply in the environment could accelerate the transformation of R. solanacearum from high virulence wild‐type into a PC‐type, probably for the purpose of adapting to the adverse environment.

中文翻译：

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过量外源氮长期胁迫下青枯病菌的表型及致病性

细菌性枯萎病是由土壤传播的病原体青枯病菌引起的，是茄科等许多植物的严重病害。为了研究土壤中积累的氮对青枯菌表型和致病性的影响，设计了连续传代实验 (SPE)。具体来说，使用略过量硫酸铵 (AS) 或硝酸铵 (AN) 的基本培养基来模拟含有过量氮的土壤的营养。30 SPE期间，监测青枯菌氮代谢基因的表型、致病性和相对表达量。表型分析结果表明，青枯菌菌落经过长期培养，菌落形态发生了变化，从高毒力、流动性强的菌落到小而圆的非粘液菌落；过度外源氮长期胁迫后的菌株为无毒力表型转化型（PC型）。暴露于外源性 AS 或 AN 后菌落形态发生变化的时间显着少于未处理的样品，后者未经外源性氮处理。致病性的结果还表明，用外源 AN 或 AS 处理的培养物比对照更快地降低毒力。AN 处理或 AS 处理的 10 SPE 的疾病指数分别比对照低 89% 或 68%。此外，随着孵育时间的增加，与未处理的样品相比，两种处理下培养物的游泳运动和生物膜形成的数量发生了显着变化。此外，在 30 SPE 后，用 AN 处理的培养物中一氧化氮还原酶 norB 基因的相对表达比对照高 1.51 倍。这些结果表明，环境中过量的氮供应可以加速青枯菌从高毒力野生型向 PC 型的转化，可能是为了适应不利环境。