Investigations of Lyme spirochete transmission as a complex network of microbial and ecological interactions

伯氏疏螺旋体(Borrelia burgdorferi，BB)通过黑腿硬蜱传播，作为北美最流行的媒介传播疾病莱姆病(Lyme Disease，LD)的病原体，对公共卫生具有日益重要的意义，其发病率不断上升。虽然经常被认为是家畜传播循环(ETC)中的病原体，但没有证据表明BB在其循环的宿主或宿主中引起疾病。在这里，我们概念化的BB感染作为一种兼性的互惠关系，这是受硬蜱内的微生物动态和组成ETC的更广泛的生态相互作用的环境的影响。肩部硬蜱是研究生态相互作用网络的一个有价值的候选者，因为它的微生物群包含了微生物与节肢动物宿主之间的一系列关系，从短暂的共生环境获得的微生物到可遗传的专性细胞内共生生物，其中最主要的是布氏立克次体。集中在假设影响Bb-ETC的相互作用，拟议的研究将表征Bb在硬蜱中的定植，评估Bb丰度和基因表达作为假定的营养内共生菌Rb和硬蜱微生物群的存在的函数的变化，其特征如下：1)细菌分类群(16S核糖体RNA)的相对丰度；2)操纵的、分类的微生物群组合(即自然现场收集的硬蜱；人工实验室饲养的；以及在无菌容器(SA1)中饲养的被破坏的实验室)。将测量BB对硬蜱生活史特征、生存、新陈代谢和行为以及相关基因表达的影响(Bb和Tick)，估计Bb-Tick关联的收益/成本，并测试可能的机制(SA2)。最后，将使用两个建模框架对BB-ETC估计和评估扁虱内、扁虱-微生物和扁虱-微生物组相互作用(BB-RB相互作用和分类组合)的累积影响。一个基于代理的模型将重点放在微生物介导的壁虱血粉充盈、发育、存活、行为和繁殖力方面的差异(SA3.1)。BB-ETC动态在更广泛的时间尺度上的分隔模型也将考虑跨多个周期的季节性。将利用与现场和实验室实验以及经验数据并行开发并由其提供信息的模型，来制定正式的壁虱向量容量定义，其中包括壁虱微生物组的重要组成部分和影响(SA3.2)。然后将利用这些结果来提高对BB-ETC的理解和对LD风险指标的预测。

Borrelia burgdorferi (Bb), transmitted via the blacklegged tick (Ixodes scapularis), is of growing public health importance as the etiologic agent of the most prevalent vector-borne disease in North America, Lyme disease (LD), which continues to increase in incidence. Although often framed as a pathogen in the Enzootic Transmission Cycle (ETC), there is no evidence that Bb elicits disease in either the reservoir or tick hosts between which it cycles. Here, we conceptualize Bb-infection in I. scapularis ticks as a facultative mutualism that is influenced by microbial dynamics within ticks and the broader context of ecological interactions between ticks and vertebrate hosts comprising the ETC. Ixodes scapularis is a valuable candidate to study networks of ecological interactions, as its microbiome encompasses the spectrum of relationships in which microbes can engage with arthropod hosts from transitory, commensal environmentally-acquired microbes to heritable obligate, intracellular endosymbionts, the most predominant of which is Rickettsia buchneri (Rb). Focusing on interactions hypothesized to influence the Bb-ETC, the proposed study will characterize Bb colonization in ticks, evaluating changes in Bb abundance and gene expression as a function of the presence of the putative nutritional endosymbiont Rb and the tick microbiome as characterized by 1) the relative abundance of bacterial taxa (16S ribosomal RNA) and 2) manipulated, categorical microbiome assemblages (i.e., natural-field collected ticks; artificial-lab reared; and disrupted-lab reared in sterile-containers (SA1). Bb effects on tick life-history traits, survival, metabolism and behavior and associated gene expression (of Bb and tick) will be measured, estimating the benefits/costs of Bb-tick associations, and testing potential mechanisms (SA2). Finally, the cumulative impacts of within-ticks, tick-microbe, and tick-microbiome interactions (Bb-Rb interactions and categorical assemblages) will be estimated and evaluated for the Bb-ETC using two modeling frameworks. An agent based model will focus on microbe-mediated differences in tick bloodmeal engorgement, development, survival, behavior, and fecundity (SA3.1). A compartmental model of Bb-ETC dynamics over a broader time scale will also consider seasonality across multiple cycles. Models, developed in parallel with and informed by field and lab experiments and empirical data will be leveraged to develop a formal tick vectorial capacity definition inclusive of important components and effects of the tick microbiome (SA3.2). These results then will be leveraged to improve understanding of Bb-ETC and prediction of LD risk indicators.