Mason Eliza, Henderson Michael W, Scheller Erich V, Byrd Matthew S, Cotter Peggy A
Department of Microbiology and Immunology, School of Medicine, University of North Carolina, Chapel Hill, NC, 27599-7290, USA.
Mol Microbiol. 2013 Nov;90(4):716-33. doi: 10.1111/mmi.12394. Epub 2013 Sep 30.
Bordetella species cause respiratory infections in mammals. Their master regulatory system BvgAS controls expression of at least three distinct phenotypic phases in response to environmental cues. The Bvg⁺ phase is necessary and sufficient for respiratory infection while the Bvg⁻ phase is required for survival ex vivo. We obtained large colony variants (LCVs) from the lungs of mice infected with B. bronchiseptica strain RBX9, which contains an in-frame deletion mutation in fhaB, encoding filamentous haemagglutinin. RBX9 also yielded LCVs when switched from Bvg⁻ phase conditions to Bvg⁺ phase conditions in vitro. We determined that LCVs are composed of both Bvg⁺ and Bvg⁻ phase bacteria and that they result from defective bvgAS positive autoregulation. The LCV phenotype was linked to the presence of a divergent promoter 5' to bvgAS, suggesting a previously undescribed mechanism of transcriptional interference that, in this case, leads to feedback-based bistability (FBM). Our results also indicate that a small proportion of RBX9 bacteria modulates to the Bvg⁻ phase in vivo. In addition to providing insight into transcriptional interference and FBM, our data provide an example of an in-frame deletion mutation exerting a 'polar' effect on nearby genes.
博德特氏菌属会引起哺乳动物的呼吸道感染。其主要调控系统BvgAS会根据环境信号控制至少三种不同表型阶段的表达。Bvg⁺阶段对于呼吸道感染是必需且充分的，而Bvg⁻阶段是体外存活所必需的。我们从感染支气管败血波氏杆菌RBX9菌株的小鼠肺部获得了大菌落变体（LCV），该菌株在编码丝状血凝素的fhaB基因中存在一个框内缺失突变。当在体外从Bvg⁻阶段条件转变为Bvg⁺阶段条件时，RBX9也会产生LCV。我们确定LCV由Bvg⁺和Bvg⁻阶段的细菌组成，并且它们是由有缺陷的bvgAS正向自动调节导致的。LCV表型与bvgAS上游5'端一个不同的启动子的存在有关，这表明了一种先前未描述的转录干扰机制，在这种情况下，会导致基于反馈的双稳态（FBM）。我们的结果还表明，一小部分RBX9细菌在体内会调节为Bvg⁻阶段。除了深入了解转录干扰和FBM外，我们的数据还提供了一个框内缺失突变对附近基因产生“极性”效应的例子。
