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

伯氏疏螺旋体（Bb）通过黑腿蜱传播，作为北美最流行的媒介传播疾病莱姆病（LD）的病原，在公共卫生方面具有越来越重要的意义，莱姆病的发病率持续增加。虽然在动物地方病传播循环（ETC）中经常被认为是一种病原体，但没有证据表明Bb在其循环的宿主或蜱虫宿主中引起疾病。在这里，我们将肩胛骨蜱中的bb感染概念为兼性互惠共生，受蜱内微生物动力学和蜱与包括ETC在内的脊椎动物宿主之间生态相互作用的更广泛背景的影响。肩胛骨棘虫是研究生态相互作用网络的有价值的候选者，因为它的微生物组包括微生物与节肢动物宿主的关系，从短暂的、共生的环境获得性微生物到遗传的专性、细胞内共生微生物，其中最主要的是布氏立克次体（Rb）。该研究将聚焦于假设影响Bb- etc的相互作用，将表征Bb在蜱虫中的定植，评估Bb丰度和基因表达的变化，作为假定的营养性内共生体Rb和蜱虫微生物组存在的函数，其特征在于1)细菌分类群（16S核糖体RNA）的相对丰度和2)被操纵的分类微生物组组合(即自然现场收集的蜱虫；人工实验室饲养的；在无菌容器中饲养的实验室（SA1）。将测量Bb对蜱虫生活史特征、生存、代谢和行为以及相关基因表达（Bb和蜱虫）的影响，估计Bb-蜱虫关联的收益/成本，并测试潜在机制（SA2）。最后，将使用两个建模框架估计和评估蜱内、蜱-微生物和蜱-微生物组相互作用（Bb-Rb相互作用和分类组合）对Bb-ETC的累积影响。基于代理的模型将侧重于微生物介导的蜱血充血、发育、生存、行为和繁殖力的差异（SA3.1）。在更广泛的时间尺度上，Bb-ETC动力学的分区模型也将考虑跨多个周期的季节性。将利用与实地和实验室实验以及经验数据并行开发的模型，制定正式的蜱虫媒介能力定义，包括蜱虫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.