Quorum size of Pseudomonas syringae is small and dictated by water availability on the leaf surface
Quorum size of Pseudomonas syringae is small and dictated by water availability on the leaf surface
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DOI：
10.1073/pnas.0711723105
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发表时间：
2008-02-26
影响因子：
11.1
通讯作者：
Lindow, Steven E.
中科院分区：
文献类型：
--
作者：
Dulla, Glenn;Lindow, Steven E.
细菌群体感应（QS），介导细胞密度依赖性基因表达的范例，通常已在高细胞密度的液体培养或在生物膜中的信号浓度积累到足够高的水平，以诱导QS的研究。据推测，在信号分子扩散受限的条件下，较小的群体大小可以实现这种QS诱导状态。植物病原性细菌假单胞菌（Pseudomonaserichingae），其中QS控制涉及附生适合性和毒性的性状，以各种大小的聚集体出现在叶表面。由于树叶往往含有有限的地表水，我们调查了聚集体的大小，将允许QS在一个不饱和的环境。QS诱导通过携带mRFP 1与ahll的转录融合物的P. lingae细胞的双重荧光可视化，ahll表现出N-酰基高丝氨酸内酯依赖性转录活性，以及组成型GFP标记物以解释叶上的所有P. lingae细胞。共聚焦显微镜显示，在湿叶上，在接种后2天内没有明显的QS诱导，但在3天和4天内，QS诱导分别随着聚集体大小>40和22个细胞/聚集体的增加而迅速增加。相比之下，QS诱导在接种于干叶后2天在>33个细胞的聚集体中是常见的，并且分别在3天和4天后随着聚集体大小>35和13个细胞的增加而迅速增加。这些观察结果表明，小群体的细胞经历QS，干燥叶片上的信号扩散受到限制的条件。在非水饱和的环境中，例如在叶片上，细菌的群体大小是小的，并且QS诱导可能是普遍操作的。
The paradigm of bacterial quorum sensing (QS), which mediates cell-density-dependent gene expression, usually has been studied in high-cell-density planktonic liquid cultures or in biofilms in which signal concentrations accumulate to sufficiently high levels to induce QS. Presumably under conditions with restricted diffusion of the signal molecule, smaller population sizes could achieve such a state of QS induction. The plant-pathogenic bacterium Pseudomonas syringae, in which QS controls traits involved in epiphytic fitness and virulence, occurs on leaf surfaces in aggregates of various sizes. Because leaves often harbor limited surface water, we investigated the size of aggregates that would permit QS in a nonsaturated environment. QS induction was visualized via dual fluorescence of P. syringae cells harboring a transcriptional fusion of mRFP1 with ahll, which exhibits N-acyl homoserine lactone-dependent transcriptional activity, and a constitutive GFP marker to account for all P. syringae cells on a leaf. Confocal microscopy revealed that, on wet leaves, no QS induction was evident within 2 days after inoculation, but it increased rapidly with increasing aggregate sizes >40 and 22 cells per aggregate by 3 and 4 days, respectively. In contrast, QS induction was common in aggregates >33 cells by 2 days after inoculation on dry leaves and increased rapidly with increasing aggregate sizes >35 and 13 cells after 3 and 4 days, respectively. These observations demonstrate that small groups of cells experience QS,conditions on dry leaves where signal diffusion is restricted. Quorum size of bacteria in non-water-saturated environments such as on leaves is small, and QS induction may be commonly operative.