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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Quorum size of Pseudomonas syringae is small and dictated by water availability on the leaf surface
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Quorum size of Pseudomonas syringae is small and dictated by water availability on the leaf surface

机译：丁香假单胞菌的法定大小很小，取决于叶片表面的水分利用率

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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.
机译：介导细胞密度依赖性基因表达的细菌群体感应（QS）范式通常已在高细胞密度浮游液体培养物或生物膜中研究，其中信号浓度积累到足够高的水平以诱导QS。据推测，在信号分子扩散受限的条件下，较小的种群规模可以实现这种QS诱导状态。植物病原性细菌丁香假单胞菌，其中QS控制参与附生适应性和毒力的性状，以各种大小的聚集体出现在叶片表面。由于叶子通常只能容纳有限的地表水，因此我们研究了在非饱和环境中允许QS的聚集体的大小。通过具有mRFP1与ahll的转录融合的丁香假单胞菌细胞的双重荧光可视化QS诱导，该融合体表现出N-酰基高丝氨酸内酯依赖的转录活性，以及​​组成型GFP标记以解释叶上所有丁香假单胞菌细胞。共聚焦显微镜显示，在湿叶上，接种后2天之内没有明显的QS诱导作用，但随着聚集体大小的增加> 40和22个细胞/聚集体分别增加3天和4天，QS诱导迅速增加。相反，在干燥叶片上接种2天后，聚集体> 33个细胞中QS诱导很常见，并且分别在3天和4天后随着聚集体尺寸增加> 35和13个细胞而迅速增加。这些观察结果表明，一小组细胞在信号扩散受到限制的干燥叶片上经历了QS条件。在非水饱和环境（例如在叶子上）中，细菌的定额很小，QS诱导通常是可行的。

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