Freed Nikki E, Silander Olin K, Stecher Bärbel, Böhm Alex, Hardt Wolf-Dietrich, Ackermann Martin
Institute of Integrative Biology, Eidgenössische Technische Hochschule (ETH) Zurich, Zurich, Switzerland.
PLoS Genet. 2008 Dec;4(12):e1000307. doi: 10.1371/journal.pgen.1000307. Epub 2008 Dec 19.
Genetically identical populations of unicellular organisms often show marked variation in some phenotypic traits. To investigate the molecular causes and possible biological functions of this phenotypic noise, it would be useful to have a method to identify genes whose expression varies stochastically on a certain time scale. Here, we developed such a method and used it for identifying genes with high levels of phenotypic noise in Salmonella enterica ssp. I serovar Typhimurium (S. Typhimurium). We created a genomic plasmid library fused to a green fluorescent protein (GFP) reporter and subjected replicate populations harboring this library to fluctuating selection for GFP expression using fluorescent-activated cell sorting (FACS). After seven rounds of fluctuating selection, the populations were strongly enriched for promoters that showed a high amount of noise in gene expression. Our results indicate that the activity of some promoters of S. Typhimurium varies on such a short time scale that these promoters can absorb rapid fluctuations in the direction of selection, as imposed during our experiment. The genomic fragments that conferred the highest levels of phenotypic variation were promoters controlling the synthesis of flagella, which are associated with virulence and host-pathogen interactions. This confirms earlier reports that phenotypic noise may play a role in pathogenesis and indicates that these promoters have among the highest levels of noise in the S. Typhimurium genome. This approach can be applied to many other bacterial and eukaryotic systems as a simple method for identifying genes with noisy expression.
基因相同的单细胞生物群体在某些表型特征上常常表现出显著差异。为了研究这种表型噪声的分子原因及可能的生物学功能，拥有一种能够识别在特定时间尺度上随机变化表达的基因的方法将很有用。在此，我们开发了这样一种方法，并将其用于鉴定肠炎沙门氏菌亚种I血清型鼠伤寒沙门氏菌（鼠伤寒沙门氏菌）中具有高水平表型噪声的基因。我们构建了一个与绿色荧光蛋白（GFP）报告基因融合的基因组质粒文库，并使用荧光激活细胞分选（FACS）对携带该文库的重复群体进行GFP表达的波动选择。经过七轮波动选择后，这些群体中大量富集了在基因表达中表现出高噪声水平的启动子。我们的结果表明，鼠伤寒沙门氏菌的一些启动子在如此短的时间尺度上发生变化，以至于这些启动子能够吸收在我们实验中施加的选择方向上的快速波动。赋予最高水平表型变异的基因组片段是控制鞭毛合成的启动子，鞭毛与毒力和宿主 - 病原体相互作用相关。这证实了早期的报道，即表型噪声可能在发病机制中起作用，并表明这些启动子在鼠伤寒沙门氏菌基因组中具有最高水平的噪声。这种方法可以作为一种识别具有噪声表达基因的简单方法应用于许多其他细菌和真核生物系统。
