Assessment of flhDC mRNA Levels in Serratia liquefaciens Swarm Cells

We reported previously that artificial overexpression of the flhDC operon in liquid-grown Serratia liquefaciens resulted in the formation of filamentous, multinucleated, and hyperflagellated cells that were indistinguishable from surface-induced swarm cells (L. Eberl, G. Christiansen, S. Molin, and M. Givskov, J. Bacteriol. 178:554–559, 1996). In the present report we show by means of reporter gene measurements, Northern analysis, and in situ reverse transcription-PCR that the amount of flhDC mRNA in surface-grown swarm cells does not exceed the maximum level found in nondifferentiated, vegetative cells. This suggests that surface-induced S. liquefaciens swarm cell differentiation, although dependent on flhDC gene expression, does not occur through elevated flhDC mRNA levels.

我们此前曾报道，在液体培养的液化沙雷氏菌（Serratia liquefaciens）中人工过表达flhDC操纵子（flhDC operon），可诱导产生丝状、多核且鞭毛富集的细胞，这类细胞与表面诱导生成的群游细胞（swarm cells）无显著差异（L. Eberl、G. Christiansen、S. Molin及M. Givskov，《Journal of Bacteriology》，178:554–559，1996）。本研究通过报告基因检测、Northern印迹分析以及原位逆转录PCR（in situ reverse transcription-PCR）证实，表面培养的群游细胞中flhDC mRNA的含量并未高于未分化营养细胞中的最高水平。这提示，尽管表面诱导的液化沙雷氏菌群游细胞分化依赖于flhDC基因的表达，但该分化过程并非通过提升flhDC mRNA的水平得以实现。