Morris Cindy E, Kinkel Linda L, Xiao Kun, Prior Philippe, Sands David C
INRA, Unité de Pathologie Végétale, BP 94, 84140 Montfavet, France.
Infect Genet Evol. 2007 Jan;7(1):84-92. doi: 10.1016/j.meegid.2006.05.002. Epub 2006 Jun 27.
The biology and ecology of plant pathogenic bacteria have been studied almost exclusively in agricultural contexts. In contrast, for numerous human pathogens their biological activity in niches outside of medical contexts is well-known. Whereas there is increasing evidence that traits fostering survival in 'environmental' niches can be the basis for virulence factors of human pathogens, niches for plant pathogenic bacteria outside of plants or of agricultural settings have not been elucidated. Most phytopathogenic bacteria are not obligate parasites, some of them can be transported to altitudes of several kilometres, they are scrubbed from the atmosphere by rainfall, and thus they are presumably transported to and might survive in a wide range of habitats. We isolated Pseudomonas syringae from river epilithon (rock-attached biofilms composed of algae, diatoms, rotifers, bacteria and nematodes) at densities up to 6000 cells g(-1) in France and the USA, some in pristine settings where waters flowed directly from snow melt and had not passed through agricultural zones. These strains induced hypersensitivity in indicator plants (tobacco) suggesting the presence of functional pathogenicity systems, and many induced disease in 1-7 of the plant species tested and produced a syringomycin-like toxin. Strains also were resistant to some antibiotics used to control plant diseases but not to copper sulphate. Sequencing of the 16S rDNA of epilithon strains and of reference strains of P. syringae revealed that a genetic lineage containing the strains with the broadest host range was distributed across several continents. Is it likely that wide spread dissemination of P. syringae occurs via aerosols and precipitation. This work highlights our limited understanding of non-agricultural niches in the ecology and evolution of plant pathogenic bacteria, of their role in the development of agricultural epidemics both as sources of inoculum and as sources of novel traits that may enhance bacterial pathogenicity and fitness.
植物致病细菌的生物学和生态学几乎完全是在农业环境中进行研究的。相比之下，对于众多人类病原体而言，它们在医学环境之外生态位中的生物活性是广为人知的。尽管越来越多的证据表明，有助于在“环境”生态位中生存的特性可能是人类病原体毒力因子的基础，但植物致病细菌在植物或农业环境之外的生态位尚未得到阐明。大多数植物致病细菌并非专性寄生菌，其中一些能够被输送到数千米的高空，会被降雨从大气中冲刷下来，因此它们可能被输送到广泛的栖息地并在其中存活。我们在法国和美国从河流附石生物（由藻类、硅藻、轮虫、细菌和线虫组成的附着在岩石上的生物膜）中分离出丁香假单胞菌，密度高达每克6000个细胞，有些分离自原始环境，那里的水流直接来自融雪且未流经农业区。这些菌株在指示植物（烟草）中引发过敏反应，表明存在功能性致病系统，并且许多菌株在1至7种受试植物物种中引发病害并产生类似丁香霉素的毒素。这些菌株还对一些用于控制植物病害的抗生素具有抗性，但对硫酸铜没有抗性。对附石生物菌株和丁香假单胞菌参考菌株的16S rDNA进行测序表明，包含宿主范围最广的菌株的一个遗传谱系分布在几个大陆。丁香假单胞菌很可能通过气溶胶和降水进行广泛传播。这项工作凸显了我们对植物致病细菌生态学和进化中非农业生态位的了解有限，以及它们在农业病害流行发展中作为接种源和可能增强细菌致病性及适应性的新特性来源所起的作用。
