Monier J-M, Lindow S E
Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA.
Proc Natl Acad Sci U S A. 2003 Dec 23;100(26):15977-82. doi: 10.1073/pnas.2436560100. Epub 2003 Dec 9.
The survival of individual Pseudomonas syringae cells was determined on bean leaf surfaces maintained under humid conditions or periodically exposed to desiccation stress. Cells of P. syringae strain B728a harboring a GFP marker gene were visualized by epifluorescence microscopy, either directly in situ or after recovery from leaves, and dead cells were identified as those that were stained with propidium iodide in such populations. Under moist, conducive conditions on plants, the proportion of total live cells was always high, irrespective of their aggregated state. In contrast, the proportion of the total cells that remained alive on leaves that were periodically exposed to desiccation stress decreased through time and was only approximately 15% after 5 days. However, the fraction of cells in large aggregates that were alive on such plants in both condition was much higher than more solitary cells. Immediately after inoculation, cells were randomly distributed over the leaf surface and no aggregates were observed. However, a very aggregated pattern of colonization was apparent within 7 days, and >90% of the living cells were located in aggregates of 100 cells or more. Our results strongly suggest that, although conducive conditions favor aggregate formation, such cells are much more capable of tolerating environmental stresses, and the preferential survival of cells in aggregates promotes a highly clustered spatial distribution of bacteria on leaf surfaces.
在保持湿润条件或定期暴露于干燥胁迫的菜豆叶表面，测定丁香假单胞菌单个细胞的存活率。携带绿色荧光蛋白（GFP）标记基因的丁香假单胞菌菌株B728a的细胞，通过落射荧光显微镜直接原位观察，或从叶片上回收后观察，死细胞被鉴定为在这类群体中被碘化丙啶染色的细胞。在植物上潮湿、适宜的条件下，无论其聚集状态如何，活细胞总数的比例始终很高。相比之下，定期暴露于干燥胁迫的叶片上存活的细胞总数比例随时间下降，5天后仅约为15%。然而，在这两种条件下，此类植物上大聚集体中存活的细胞比例远高于较为分散的细胞。接种后立即观察到，细胞随机分布在叶表面，未观察到聚集体。然而，7天内明显出现了非常聚集的定殖模式，超过90%的活细胞位于100个或更多细胞的聚集体中。我们的结果有力地表明，尽管适宜条件有利于聚集体形成，但此类细胞更能耐受环境胁迫，聚集体中细胞的优先存活促进了细菌在叶表面的高度聚集空间分布。
