Ohnishi J, Piesman J, de Silva A M
Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, NC 27599, USA.
Proc Natl Acad Sci U S A. 2001 Jan 16;98(2):670-5. doi: 10.1073/pnas.98.2.670.
The genome of Borrelia burgdorferi encodes a large number of lipoproteins, many of which are expressed only at certain stages of the spirochete's life cycle. In the current study we describe the B. burgdorferi population structure with respect to the production of two lipoproteins [outer surface protein A (OspA) and outer surface protein C (OspC)] during transmission from the tick vector to the mammalian host. Before the blood meal, the bacteria in the tick were a homogeneous population that mainly produced OspA only. During the blood meal, the population became more heterogeneous; many bacteria produced both OspA and OspC, whereas others produced only a single Osp and a few produced neither Osp. From the heterogeneous spirochetal population in the gut, a subset depleted of OspA entered the salivary glands and stably infected the host at time points >53 hr into the blood meal. We also examined genetic heterogeneity at the B. burgdorferi vlsE locus before and during the blood meal. In unfed ticks, the vlsE locus was stable and one predominant and two minor alleles were detected. During the blood meal, multiple vlsE alleles were observed in the tick. Tick feeding may increase recombination at the vlsE locus or selectively amplify rare vlsE alleles present in unfed ticks. On the basis of our data we propose a model, which is different from the established model for B. burgdorferi transmission. Implicit in our model is the concept that tick transmission converts a homogeneous spirochete population into a heterogeneous population that is poised to infect the mammalian host.
伯氏疏螺旋体的基因组编码大量脂蛋白，其中许多仅在螺旋体生命周期的特定阶段表达。在本研究中，我们描述了伯氏疏螺旋体在从蜱虫载体传播到哺乳动物宿主过程中，两种脂蛋白[外表面蛋白A（OspA）和外表面蛋白C（OspC）]产生情况的种群结构。在蜱虫吸血前，蜱虫体内的细菌是一个主要仅产生OspA的同质种群。在吸血过程中，种群变得更加异质化；许多细菌同时产生OspA和OspC，而其他细菌仅产生单一的Osp，还有少数细菌既不产生OspA也不产生OspC。从肠道中的异质螺旋体种群中，一个不含OspA的亚群进入唾液腺，并在吸血53小时后稳定感染宿主。我们还检测了吸血前后伯氏疏螺旋体vlsE位点的遗传异质性。在未吸血的蜱虫中，vlsE位点是稳定的，检测到一个主要等位基因和两个次要等位基因。在吸血过程中，在蜱虫中观察到多个vlsE等位基因。蜱虫吸血可能会增加vlsE位点的重组，或选择性扩增未吸血蜱虫中存在的罕见vlsE等位基因。基于我们的数据，我们提出了一个与已建立的伯氏疏螺旋体传播模型不同的模型。我们模型中隐含的概念是，蜱虫传播将同质的螺旋体种群转变为一个准备感染哺乳动物宿主的异质种群。
