Caimano Melissa J, Iyer Radha, Eggers Christian H, Gonzalez Cynthia, Morton Elizabeth A, Gilbert Michael A, Schwartz Ira, Radolf Justin D
Department of Medicine, University of Connecticut Health Center, Farmington, CT 06030, USA.
Mol Microbiol. 2007 Sep;65(5):1193-217. doi: 10.1111/j.1365-2958.2007.05860.x. Epub 2007 Jul 23.
Borrelia burgdorferi (Bb) adapts to its arthropod and mammalian hosts by altering its transcriptional and antigenic profiles in response to environmental signals associated with each of these milieus. In studies presented here, we provide evidence to suggest that mammalian host signals are important for modulating and maintaining both the positive and negative aspects of mammalian host adaptation mediated by the alternative sigma factor RpoS in Bb. Although considerable overlap was observed between genes induced by RpoS during growth within the mammalian host and following temperature-shift, comparative microarray analyses demonstrated unequivocally that RpoS-mediated repression requires mammalian host-specific signals. A substantial portion of the in vivo RpoS regulon was uniquely upregulated within dialysis membrane chambers, further underscoring the importance of host-derived environmental stimuli for differential gene expression in Bb. Expression profiling of genes within the RpoS regulon by quantitative reverse transcription polymerase chain reaction (qRT-PCR) revealed a level of complexity to RpoS-dependent gene regulation beyond that observed by microarray, including a broad range of expression levels and the presence of genes whose expression is only partially dependent on RpoS. Analysis of Bb-infected ticks by qRT-PCR established that expression of rpoS is induced during the nymphal blood meal but not within unfed nymphs or engorged larvae. Together, these data have led us to postulate that RpoS acts as a gatekeeper for the reciprocal regulation of genes involved in the establishment of infection within the mammalian host and the maintenance of spirochetes within the arthropod vector.
伯氏疏螺旋体（Bb）通过响应与这些环境相关的环境信号改变其转录和抗原谱，从而适应其节肢动物和哺乳动物宿主。在本文所呈现的研究中，我们提供证据表明，哺乳动物宿主信号对于调节和维持由Bb中的替代sigma因子RpoS介导的哺乳动物宿主适应性的正负两方面都很重要。尽管在哺乳动物宿主内生长期间以及温度转变后由RpoS诱导的基因之间观察到相当大的重叠，但比较微阵列分析明确表明，RpoS介导的抑制需要哺乳动物宿主特异性信号。体内RpoS调控子的很大一部分在透析膜小室中被独特地上调，进一步强调了宿主衍生的环境刺激对于Bb中差异基因表达的重要性。通过定量逆转录聚合酶链反应（qRT-PCR）对RpoS调控子内的基因进行表达谱分析，揭示了RpoS依赖性基因调控的复杂程度超出了微阵列观察到的范围，包括广泛的表达水平以及存在其表达仅部分依赖于RpoS的基因。通过qRT-PCR对感染Bb的蜱进行分析表明，rpoS的表达在若虫吸血期间被诱导，但在未进食的若虫或饱血幼虫中未被诱导。总之，这些数据使我们推测，RpoS充当了参与哺乳动物宿主内感染建立和节肢动物载体中螺旋体维持的基因相互调控的守门人。
