Grenier Anne-Marie, Duport Gabrielle, Pagès Sylvie, Condemine Guy, Rahbé Yvan
Laboratoire de Biologie Fonctionnelle Insectes et Interactions, BF2I, UMR 203 INRA-INSA de Lyon, Bat. L.-Pasteur, F-69621 Villeurbanne Cedex, France.
Appl Environ Microbiol. 2006 Mar;72(3):1956-65. doi: 10.1128/AEM.72.3.1956-1965.2006.
Dickeya dadantii (Erwinia chrysanthemi) is a phytopathogenic bacterium causing soft rot diseases on many crops. The sequencing of its genome identified four genes encoding homologues of the Cyt family of insecticidal toxins from Bacillus thuringiensis, which are not present in the close relative Pectobacterium carotovorum subsp. atrosepticum. The pathogenicity of D. dadantii was tested on the pea aphid Acyrthosiphon pisum, and the bacterium was shown to be highly virulent for this insect, either by septic injury or by oral infection. The lethal inoculum dose was calculated to be as low as 10 ingested bacterial cells. A D. dadantii mutant with the four cytotoxin genes deleted showed a reduced per os virulence for A. pisum, highlighting the potential role of at least one of these genes in pathogenicity. Since only one bacterial pathogen of aphids has been previously described (Erwinia aphidicola), other species from the same bacterial group were tested. The pathogenic trait for aphids was shown to be widespread, albeit variable, within the phytopathogens, with no link to phylogenetic positioning in the Enterobacteriaceae. Previously characterized gut symbionts from thrips (Erwinia/Pantoea group) were also highly pathogenic to the aphid, whereas the potent entomopathogen Photorhabdus luminescens was not. D. dadantii is not a generalist insect pathogen, since it has low pathogenicity for three other insect species (Drosophila melanogaster, Sitophilus oryzae, and Spodoptera littoralis). D. dadantii was one of the most virulent aphid pathogens in our screening, and it was active on most aphid instars, except for the first one, probably due to anatomical filtering. The observed difference in virulence toward apterous and winged aphids may have an ecological impact, and this deserves specific attention in future research.
胡萝卜软腐果胶杆菌（菊欧文氏菌）是一种能在多种作物上引发软腐病的植物致病细菌。其基因组测序鉴定出四个编码苏云金芽孢杆菌杀虫毒素Cyt家族同源物的基因，而其近缘种黑胫果胶杆菌中不存在这些基因。对豌豆蚜进行了胡萝卜软腐果胶杆菌的致病性测试，结果表明，无论是通过败血症损伤还是口服感染，该细菌对这种昆虫都具有高毒性。计算得出致死接种剂量低至10个摄入的细菌细胞。一个缺失了四个细胞毒素基因的胡萝卜软腐果胶杆菌突变体对豌豆蚜的经口毒性降低，这突出了这些基因中至少一个在致病性中的潜在作用。由于此前仅描述过一种蚜虫的细菌病原体（蚜虫欧文氏菌），因此对同一细菌类群的其他物种进行了测试。结果表明，蚜虫致病特性在植物病原体中广泛存在，尽管存在差异，且与肠杆菌科中的系统发育定位无关。此前鉴定的蓟马肠道共生菌（欧文氏菌/泛菌属）对蚜虫也具有高致病性，而强效昆虫病原体发光光杆状菌则不然。胡萝卜软腐果胶杆菌不是一种广谱昆虫病原体，因为它对其他三种昆虫物种（黑腹果蝇、米象和滨海灰翅夜蛾）的致病性较低。在我们的筛选中，胡萝卜软腐果胶杆菌是毒性最强的蚜虫病原体之一，它对除第一龄期外的大多数蚜虫龄期都有活性，这可能是由于解剖学过滤的原因。观察到的对无翅和有翅蚜虫毒力的差异可能具有生态影响，这在未来的研究中值得特别关注。
