Awuoche Erick O, Smallenberger Gretchen, Bruzzese Daniel L, Orfano Alessandra, Weiss Brian L, Aksoy Serap
Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, United States of America.
PLoS Pathog. 2025 Jan 31;21(1):e1012692. doi: 10.1371/journal.ppat.1012692. eCollection 2025 Jan.
Tsetse flies (Glossina spp.) vector African trypanosomes that cause devastating diseases in humans and domestic animals. Within the Glossina genus, species in the Palpalis subgroup exhibit greater resistance to trypanosome infections compared to those in the Morsitans subgroup. Varying microbiota composition and species-specific genetic traits can significantly influence the efficiency of parasite transmission. Notably, infections with the endosymbiotic bacterium Spiroplasma have been documented in several Palpalis subgroup species, including Glossina fuscipes fuscipes (Gff). While Spiroplasma infections in Gff are known to hinder trypanosome transmission, the underlying mechanisms remain unknown. To investigate Spiroplasma-mediated factors affecting Gff vector competence, we conducted high-throughput RNA sequencing of the gut tissue along with functional assays. Our findings reveal elevated oxidative stress in the gut environment in the presence of Spiroplasma, evidenced by increased expression of nitric oxide synthase, which catalyzes the production of trypanocidal nitric oxide. Additionally, we observed impaired lipid biosynthesis leading to a reduction of this important class of nutrients essential for parasite and host physiologies. In contrast, trypanosome infections in Gff's midgut significantly upregulated various immunity-related genes, including a small peptide, Stomoxyn-like, homologous to Stomoxyn first discovered in the stable fly, Stomoxys calcitrans. We observed that the Stomoxyn-like locus is exclusive to the genomes of Palpalis subgroup tsetse species. GffStomoxyn is constitutively expressed in the cardia (proventriculus) and synthetic GffStomoxyn exhibits potent activity against Escherichia coli and bloodstream form of Trypanosoma brucei parasites, while showing no effect against insect stage procyclic forms or tsetse's commensal endosymbiont Sodalis in vitro. Reducing GffStomoxyn levels significantly increased trypanosome infection prevalence, indicating its potential trypanocidal role in vivo. Collectively, our results suggest that the enhanced resistance to trypanosomes observed in Spiroplasma-infected Gff may be due to the reduced lipid availability necessary for parasite metabolic maintenance. Furthermore, GffStomoxyn could play a crucial role in the initial immune response(s) against mammalian parasites early in the infection process in the gut and prevent gut colonization. We discuss the molecular characteristics of GffStomoxyn, its spatial and temporal expression regulation and its microbicidal activity against Trypanosome parasites. Our findings reinforce the nutritional influences of microbiota on host physiology and host-pathogen dynamics.
采采蝇（舌蝇属）传播导致人类和家畜患上毁灭性疾病的非洲锥虫。在舌蝇属中， palpalis亚组的物种比 morsitans亚组的物种对锥虫感染表现出更强的抵抗力。不同的微生物群组成和物种特异性遗传特征会显著影响寄生虫传播的效率。值得注意的是，在包括fuscipes fuscipes（Gff）在内的几个 palpalis亚组物种中已记录到内共生细菌螺原体的感染。虽然已知Gff中的螺原体感染会阻碍锥虫传播，但其潜在机制仍不清楚。为了研究螺原体介导的影响Gff媒介能力的因素，我们对肠道组织进行了高通量RNA测序并进行了功能分析。我们的研究结果表明，在存在螺原体的情况下，肠道环境中的氧化应激升高，这通过一氧化氮合酶表达的增加得到证明，一氧化氮合酶催化产生具有杀锥虫作用的一氧化氮。此外，我们观察到脂质生物合成受损，导致对寄生虫和宿主生理至关重要的这一重要营养类别减少。相比之下，Gff中肠的锥虫感染显著上调了各种免疫相关基因，包括一种小肽，类似Stomoxyn，与最初在厩螫蝇中发现的Stomoxyn同源。我们观察到类似Stomoxyn的基因座是 palpalis亚组采采蝇物种基因组所特有的。GffStomoxyn在贲门（前胃）中组成性表达，合成的GffStomoxyn对大肠杆菌和布氏锥虫的血流形式寄生虫表现出强大的活性，而在体外对昆虫阶段的前循环形式或采采蝇的共生内共生菌 Sodalis没有影响。降低GffStomoxyn水平会显著增加锥虫感染的患病率，表明其在体内具有潜在的杀锥虫作用。总体而言，我们的结果表明，在感染螺原体的Gff中观察到的对锥虫抵抗力增强可能是由于寄生虫代谢维持所需的脂质可用性降低。此外，GffStomoxyn可能在感染过程早期肠道中针对哺乳动物寄生虫的初始免疫反应中发挥关键作用，并防止肠道定植。我们讨论了GffStomoxyn的分子特征、其时空表达调控及其对锥虫寄生虫的杀菌活性。我们的研究结果强化了微生物群对宿主生理和宿主 - 病原体动态的营养影响。
