Mazurier Sylvie, Corberand Thérèse, Lemanceau Philippe, Raaijmakers Jos M
INRA, Université de Bourgogne, UMR 1229 Microbiologie des Sols et de l'Environnement, Dijon cedex, France.
ISME J. 2009 Aug;3(8):977-91. doi: 10.1038/ismej.2009.33. Epub 2009 Apr 16.
Natural disease-suppressive soils provide an untapped resource for the discovery of novel beneficial microorganisms and traits. For most suppressive soils, however, the consortia of microorganisms and mechanisms involved in pathogen control are unknown. To date, soil suppressiveness to Fusarium wilt disease has been ascribed to carbon and iron competition between pathogenic Fusarium oxysporum and resident non-pathogenic F. oxysporum and fluorescent pseudomonads. In this study, the role of bacterial antibiosis in Fusarium wilt suppressiveness was assessed by comparing the densities, diversity and activity of fluorescent Pseudomonas species producing 2,4-diacetylphloroglucinol (DAPG) (phlD+) or phenazine (phzC+) antibiotics. The frequencies of phlD+ populations were similar in the suppressive and conducive soils but their genotypic diversity differed significantly. However, phlD genotypes from the two soils were equally effective in suppressing Fusarium wilt, either alone or in combination with non-pathogenic F. oxysporum strain Fo47. A mutant deficient in DAPG production provided a similar level of control as its parental strain, suggesting that this antibiotic does not play a major role. In contrast, phzC+ pseudomonads were only detected in the suppressive soil. Representative phzC+ isolates of five distinct genotypes did not suppress Fusarium wilt on their own, but acted synergistically in combination with strain Fo47. This increased level of disease suppression was ascribed to phenazine production as the phenazine-deficient mutant was not effective. These results suggest, for the first time, that redox-active phenazines produced by fluorescent pseudomonads contribute to the natural soil suppressiveness to Fusarium wilt disease and may act in synergy with carbon competition by resident non-pathogenic F. oxysporum.
天然抑病土壤为发现新型有益微生物及其特性提供了尚未开发的资源。然而，对于大多数抑病土壤而言，参与病原菌控制的微生物群落及其机制尚不清楚。迄今为止，土壤对枯萎病的抑制作用归因于致病尖孢镰刀菌与土壤中存在的非致病尖孢镰刀菌及荧光假单胞菌之间的碳和铁竞争。在本研究中，通过比较产生2,4 - 二乙酰基间苯三酚（DAPG）（phlD+）或吩嗪（phzC+）抗生素的荧光假单胞菌的密度、多样性和活性，评估了细菌抗生作用在枯萎病抑制中的作用。phlD+菌群在抑病土壤和感病土壤中的频率相似，但其基因型多样性存在显著差异。然而，来自这两种土壤的phlD基因型，无论单独使用还是与非致病尖孢镰刀菌菌株Fo47联合使用，在抑制枯萎病方面同样有效。一个缺乏DAPG产生能力的突变体与其亲本菌株对病害的控制水平相似，这表明这种抗生素并不起主要作用。相比之下，phzC+假单胞菌仅在抑病土壤中被检测到。五个不同基因型的代表性phzC+分离株单独使用时不能抑制枯萎病，但与菌株Fo47联合使用时具有协同作用。这种增强的病害抑制水平归因于吩嗪的产生，因为缺乏吩嗪的突变体无效。这些结果首次表明，荧光假单胞菌产生的具有氧化还原活性的吩嗪有助于土壤对枯萎病的天然抑制作用，并且可能与土壤中存在的非致病尖孢镰刀菌的碳竞争协同发挥作用。
