Laboratory of Bacteriology, Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, Montana, USA.
Department of Pathology and Laboratory Medicine, University of Texas Medical School at Houston, Houston, Texas, USA.
Microbiol Spectr. 2023 Jun 15;11(3):e0047723. doi: 10.1128/spectrum.00477-23. Epub 2023 Apr 3.
The highly segmented genome of Borrelia burgdorferi, the tick-borne bacterium that causes Lyme disease, is composed of a linear chromosome and more than 20 co-existing endogenous plasmids. Many plasmid-borne genes are unique to B. burgdorferi and some have been shown to provide essential functions at discrete points of the infectious cycle between a tick vector and rodent host. In this study, we investigated the role of , a highly conserved and differentially expressed gene on a ubiquitous linear plasmid of B. burgdorferi. In a prior genome-wide analysis, inactivation of by transposon insertion was linked with a noninfectious phenotype in mice, suggesting that conservation of the gene in the Lyme disease spirochete reflected a critical function of the encoded protein. To address this hypothesis, we moved the allele into a similar wild-type background and compared the phenotypes of isogenic wild-type, mutant and complemented strains and throughout the mouse/tick infectious cycle. In contrast to the previous study, we identified no defect in the ability of the mutant to colonize the tick vector or murine host, or to be efficiently transmitted between them. We conclude that joins a growing list of unique, highly conserved, yet fully dispensable plasmid-borne genes of the Lyme disease spirochete. We infer that the experimental infectious cycle, while including the tick vector and murine host, lacks key selective forces imposed during the natural enzootic cycle. The key finding of this study contradicts our premise that the ubiquitous presence and strict sequence conservation of a unique gene in the Lyme disease spirochete, Borrelia burgdorferi, reflect a critical role in either the murine host or tick vector in which these bacteria are maintained in nature. Instead, the outcome of this investigation illustrates the inadequate nature of the experimental infectious cycle currently employed in the laboratory to fully model the enzootic cycle of the Lyme disease spirochete. This study also highlights the importance of complementation for accurate interpretation of mutant phenotypes in genetic studies of Borrelia burgdorferi.
伯氏疏螺旋体的高度分段基因组由线性染色体和 20 多个共存的内源性质粒组成，该螺旋体是一种 tick-borne bacterium，可引起莱姆病。许多质粒携带的基因是伯氏疏螺旋体所特有的，有些基因已被证明在 tick 载体和啮齿动物宿主之间的传染性循环的离散点提供了必要的功能。在这项研究中，我们研究了 ，一个普遍存在的线性质粒上高度保守且差异表达的基因的作用。在之前的全基因组分析中，通过转座子插入失活 与小鼠中的非传染性表型相关，这表明该基因在莱姆病螺旋体中的保守反映了编码蛋白的关键功能。为了验证这一假设，我们将 等位基因转移到类似的野生型背景中，并比较了同源野生型、突变体和互补菌株 在整个小鼠/蜱感染循环中的表型。与之前的研究相反，我们没有发现 突变体在定殖蜱载体或鼠宿主、或在它们之间有效传播的能力方面存在缺陷。我们得出的结论是， 加入了一个不断增长的独特、高度保守但完全可缺失的莱姆病螺旋体质粒携带基因列表。我们推断，虽然实验性感染循环包括 tick 载体和鼠宿主，但缺乏在自然地方性循环中施加的关键选择压力。这项研究的关键发现与我们的前提相矛盾，即莱姆病螺旋体 Borrelia burgdorferi 中普遍存在和严格序列保守的独特基因的存在反映了这些细菌在自然界中维持的鼠宿主或 tick 载体中的关键作用。相反，这项研究的结果说明了目前实验室中使用的实验性感染循环在充分模拟莱姆病螺旋体的地方性循环方面的不足。这项研究还强调了在 Borrelia burgdorferi 的遗传研究中进行准确的突变体表型解释时，互补的重要性。
