Sodalis glossinidius iron acquisition

描述(由申请者提供)：软糖是一种兼性胞内细菌，是采采蝇的次生共生体，采采蝇携带导致非洲昏睡病的锥虫。虽然早在20世纪80年代中期就有证据表明采采蝇细胞内存在Sodalis，但使这种兼性内共生菌在采采蝇体内生存和繁殖的生理过程以及细胞内环境的研究才刚刚开始。研究这些过程将有助于PI研究的长期科学目标，即确定兼性胞内细菌在宿主内生存和/或繁殖所采用的代谢和生理过程，以及调节这些环境中基因表达的元素。这个项目的科学目标是测试假说，这些假说解决了假定的苏丹花铁获取系统对苏丹花在昆虫细胞和采采蝇中的生长的贡献。一个系统(heMR/hemTUV)被预测为编码转运蛋白，介导作为铁源的血红素的获取。由于采采蝇血粉在中肠中被消化，释放出游离的血红素，因此住在中肠组织中的苏丹红应该很容易获得。第二个系统被预测为编码一个亲和力较高的铁的亲和力较高的亲和力铁载体系统。当Sodalis在采采蝇细胞内和/或在游离铁含量有限的其他环境中时，该系统可能很重要。在具体目标1和2中，将研究苏丹红血红素和去铬转运蛋白转运蛋白突变体在采采蝇和昆虫培养中生长的能力，以检验与哪些苏丹红铁获取基因对苏丹红在这些环境中的生长重要这一问题有关的假说。在具体目标3中，将通过分析Sodalis heme和achromobactin转运蛋白突变体在以血红素或Ferri-achromobactin作为唯一铁源的介质中的生长，以及通过在不能使用血红素或achromobactin作为铁源的异源细菌中重组Sodalis系统，来评估推定的Sodalis血红素和去铬bactin转运蛋白的功能。研究采采蝇与苏打的共生关系对公共卫生具有重要意义。采采蝇体内Sodalis的存在可能会增加采采蝇对锥虫的传播，最近的研究表明，副转基因可能是一种有效的非洲锥虫病控制策略。出于这些原因，更全面地了解苏丹斯-采采子共生的性质将产生有助于控制采采子传播疾病的信息。 公共卫生相关性：采采热传播的锥虫病是一个重大的全球卫生负担，威胁着撒哈拉以南非洲的数百万人。由于采采蝇体内Sodalis的存在可能增加采采蝇对锥虫的传播，而且最近的研究表明，修改Sodalis glossinidius(采采蝇携带的一种细菌物种)可能是非洲锥虫病的有效控制策略，因此更全面地了解Sodalis与采采蝇共生的性质将产生帮助控制采采病传播的信息。最后，由于Sodalis是少数几种在宿主外培养的细胞内昆虫共生体之一，它可以被开发为研究其他影响昆虫传播疾病能力的细胞内昆虫共生体的模型。

DESCRIPTION (provided by applicant): Sodalis glossinidius is a facultative intracellular bacterium that is a secondary symbiont of the tsetse fly, which carries the trypanosome that causes African sleeping sickness. Although the presence of Sodalis within the cells of the tsetse fly has been documented since the mid-1980s, the physiological processes that enable this facultative endosymbiotic bacterium to survive and multiply within the tsetse fly and the intracellular environment are just beginning to be examined. Investigating these processes will contribute to the long-term scientific goals of the PIs research, which are to identify the metabolic and physiological processes that facultative intracellular bacteria employ to survive and/or multiply within their hosts, as well as the elements that regulate gene expression in these environments. The scientific goals of this project are to test hypotheses which address the contribution of putative Sodalis iron acquisition systems to growth of Sodalis within insect cells and the tsetse fly. One system (HemR/HemTUV) is predicted to encode transport proteins that mediate acquisition of heme as an iron source. Heme should be readily available to Sodalis residing in midgut tissue since the tsetse fly blood meal is digested in the midgut to release free heme. The second system is predicted to encode an achromobactin siderophore system that mediates high affinity iron acquisition. This system may be important when Sodalis is within the tsetse fly cells and/or in other environments where free iron is in limiting quantities. In Specific Aims 1 and 2, the ability of the Sodalis heme and achromobactin transporter mutants to grow in tsetse flies and in insect culture will be examined to test hypotheses related to the question of which Sodalis iron acquisition genes are important for growth of Sodalis in these environments. In Specific Aim 3, the function of the putative Sodalis heme and achromobactin transporters will be assessed by analyzing growth of the Sodalis heme and achromobactin transporter mutants in media with either heme or ferri- achromobactin as a sole iron source and by reconstituting the Sodalis systems in heterologous bacterial strains that cannot use heme or achromobactin as iron sources. Studying the tsetse fly-Sodalis symbiosis will have significance to public health. The presence of Sodalis in the tsetse fly may increase tsetse-mediated transmission of the trypanosome, and recent research suggests that paratransgenesis may be a useful control strategy for African trypanosomiasis. For these reasons, a more complete understanding of the nature of the Sodalis-tsetse symbiosis will yield information to help control tsetse-borne disease. PUBLIC HEALTH RELEVANCE: Tsetse-transmitted trypanosomiasis represents a significant global health burden, threatening millions of people in sub-Saharan Africa. Since the presence of Sodalis in the tsetse fly may increase tsetse-mediated transmission of the trypanosome and since recent research suggests that modifying Sodalis glossinidius (one of the bacterial species harbored by the tsetse fly) may be a useful control strategy for African trypanosomiasis, a more complete understanding of the nature of the Sodalis-tsetse symbiosis will yield information to help control tsetse-borne disease. Finally, because Sodalis is one of only a few intracellular insect symbionts to be cultured outside of the host, it can be developed as a model for the study of other intracellular insect symbionts that have an impact on the ability of the insect to transmit disease.