Department of Food Science and Nutrition, University of Minnesota, St. Paul, Minnesota, USA.
Appl Environ Microbiol. 2012 Mar;78(6):1752-64. doi: 10.1128/AEM.07454-11. Epub 2012 Jan 13.
An increasing number of outbreaks of gastroenteritis recently caused by Escherichia coli O157:H7 have been linked to the consumption of leafy green vegetables. Although it is known that E. coli survives and grows in the phyllosphere of lettuce plants, the molecular mechanisms by which this bacterium associates with plants are largely unknown. The goal of this study was to identify E. coli genes relevant to its interaction, survival, or attachment to lettuce leaf surfaces, comparing E. coli K-12, a model system, and E. coli O157:H7, a pathogen associated with a large number of outbreaks. Using microarrays, we found that upon interaction with intact leaves, 10.1% and 8.7% of the 3,798 shared genes were differentially expressed in K-12 and O157:H7, respectively, whereas 3.1% changed transcript levels in both. The largest group of genes downregulated consisted of those involved in energy metabolism, including tnaA (33-fold change), encoding a tryptophanase that converts tryptophan into indole. Genes involved in biofilm modulation (bhsA and ybiM) and curli production (csgA and csgB) were significantly upregulated in E. coli K-12 and O157:H7. Both csgA and bhsA (ycfR) mutants were impaired in the long-term colonization of the leaf surface, but only csgA mutants had diminished ability in short-term attachment experiments. Our data suggested that the interaction of E. coli K-12 and O157:H7 with undamaged lettuce leaves likely is initiated via attachment to the leaf surface using curli fibers, a downward shift in their metabolism, and the suppression of biofilm formation.
最近，越来越多的由大肠杆菌 O157:H7 引起的肠胃炎爆发与食用叶菜有关。虽然已知大肠杆菌在生菜植物的叶际中存活和生长，但这种细菌与植物相关联的分子机制在很大程度上是未知的。本研究的目的是鉴定与大肠杆菌与生菜叶表面相互作用、存活或附着相关的基因，比较模型系统大肠杆菌 K-12 和与大量爆发相关的病原体大肠杆菌 O157:H7。使用微阵列，我们发现与完整叶片相互作用时，3798 个共享基因中分别有 10.1%和 8.7%的基因在 K-12 和 O157:H7 中差异表达，而 3.1%的基因在两者中改变了转录水平。下调基因中最大的一组包括那些参与能量代谢的基因，包括编码将色氨酸转化为吲哚的色氨酸酶的 tnaA（33 倍变化）。生物膜调节（bhsA 和 ybiM）和卷曲生产（csgA 和 csgB）相关基因在大肠杆菌 K-12 和 O157:H7 中显著上调。csgA 和 bhsA（ycfR）突变体在叶片表面的长期定植中受损，但只有 csgA 突变体在短期附着实验中能力下降。我们的数据表明，大肠杆菌 K-12 和 O157:H7 与未受损生菜叶片的相互作用可能是通过卷曲纤维附着在叶片表面开始的，其代谢向下转移，生物膜形成受到抑制。
