Endosymbiont mediated chitin catabolism in the tsetse fly gut impacts trypanosome transmission

大多数节肢动物的中肠由围食基质（PM）内衬，所述围食基质由几丁质骨架组成， 其组装多种糖胺聚糖和蛋白质。PM在节肢动物中起防御作用 通过保护中肠上皮细胞免受研磨性食物颗粒的影响，调节摄入毒素的运动， 作为防止病原体感染建立的物理屏障。一些媒介传播的原生动物病原体， 包括蚊子传播的疟原虫和白蛉传播的利什曼原虫，分泌几丁质酶， 降解PM-结合甲壳素。然而，采采蝇传播的非洲锥虫不产生几丁质酶， 这些寄生虫用来规避采采蝇PM的机制还知之甚少。 除了可能被非洲锥虫感染外，所有采采蝇在分类学上都有一种 内共生细菌的可变群落。锥虫通过采采蝇传播的成功 媒介的传播部分取决于苍蝇和这些细菌之间的生理相互作用。采采蝇的一种 内共生体Sodalis glossinidius在所有实验室定殖蝇中表现出均匀分布 以及野生蝇种群内和种群间的异质分布。几个独立的领域和 基于实验室的研究已经反复证明了存在和密度之间的正相关性 在采采蝇的中肠Sodalis和锥虫的能力，成功地建立在苍蝇感染。的 这种相关性背后的机制从未被确定。在这个应用中，我们的跨学科 一个研究小组将解决这一假设，即Sodalis分泌的内切几丁质酶降解几丁质 采采蝇首相的骨干我们推测，Sodalis介导的PM相关几丁质的降解促进了 锥虫感染的建立有两种途径。首先，这一过程将损害结构完整性 从而使锥虫更容易穿过。第二，甲壳素催化剂在生产中的应用 N-乙酰基-D-葡糖胺，这是一种有效的杀锥虫凝集素抑制剂。我们建议使用索达利斯突变体 其不能产生内切几丁质酶以功能性地表征细菌之间的三方关系， 采采蝇的PM，和锥虫感染建立在苍蝇的中肠。此外，我们建议使用field 捕获的采采蝇，以确定它们的Sodalis是否产生内切几丁质酶， 采采蝇主人的首相完成本申请中提出的实验将增加我们的 了解介导锥虫通过 采采蝇载体，并可能对新的疾病控制的发展具有翻译意义 战略布局此外，本文获得的知识将适用于其他节肢动物载体模型系统 (e.g.,蚊子，蜱，白蛉），这些细菌含有中肠相关的细菌，并且具有病原体必须 为了传播给新的脊椎动物宿主而进行杂交。

The midgut of most arthropods is lined by a peritrophic matrix (PM) that is composed of a chitin backbone upon which assemble a variety of glycosaminoglycans and proteins. The PM serves a defensive role within arthropods by protecting their midgut epithelia from abrasive food particles, regulating the movement of ingested toxins, and serving as a physical barrier against pathogen infection establishment. Some vector-borne protozoan pathogens, including mosquito-transmitted Plasmodium and sand fly-transmitted Leishmania, secrete chitinases that can degrade PM-associated chitin. However, tsetse fly-transmitted African trypanosomes do not produce chitinase, and the mechanism(s) these parasites use to circumvent tsetse’s PM are poorly understood. In addition to potentially being infected with African trypanosomes, all tsetse flies harbor a taxonomically variable community of endosymbiotic bacteria. The success of trypanosome transmission through the tsetse vector depends in part on physiological interactions between the fly and these bacteria. One of tsetse’s endosymbionts, Sodalis glossinidius, exhibits a homogeneous distribution within all laboratory colonized flies and a heterogeneous distribution within and between wild fly populations. Several independent field and laboratory-based studies have repeatedly demonstrated a positive correlation between the presence and density of Sodalis in tsetse’s midgut and the ability of trypanosomes to successfully establish an infection in the fly. The mechanisms that underlie this correlation have never been determined. In this application our interdisciplinary research team will address the hypothesis that a Sodalis secreted endochitinase degrades the chitinous backbone of tsetse’s PM. We speculate that Sodalis-mediated degradation of PM-associated chitin facilitates trypanosome infection establishment in two ways. First, this process would compromise the structural integrity of the PM, thus making it easier for trypanosomes to cross. Second, chitin catabolism results in the production of N-acetyl-D-glucosamine, which is a potent inhibitor of trypanocidal lectins. We propose to use Sodalis mutants that cannot produce endochitinase to functionally characterize the tripartite relationship between the bacterium, tsetse’s PM, and trypanosome infection establishment in the fly’s midgut. Additionally, we propose to use field captured tsetse flies to determine if their Sodalis produce endochitinase that mediates the structural integrity of their tsetse host’s PM. Completion of the experiments proposed in this application will increase our understanding of the basic physiological mechanisms that mediated trypanosome transmission through the tsetse vector and may have translational implications towards the development of novel disease control strategies. Additionally, knowledge obtained herein will be applicable to other arthropod vector model systems (e.g., mosquitoes, ticks, sandflies) that house midgut-associated bacteria and have a PM that pathogens must cross in order to be transmitted to a new vertebrate host.