Diplomonad parasites of the genus Giardia have adapted to colonizing different hosts, most notably the intestinal tract of mammals. The human-pathogenic Giardia species, Giardia intestinalis, has been extensively studied at the genome and gene expression level, but no such information is available for other Giardia species. Comparative data would be particularly valuable for Giardia muris, which colonizes mice and is commonly used as a prototypic in vivo model for investigating host responses to intestinal parasitic infection. Here we report the draft-genome of G. muris. We discovered a highly streamlined genome, amongst the most densely encoded ever described for a nuclear eukaryotic genome. G. muris and G. intestinalis share many known or predicted virulence factors, including cysteine proteases and a large repertoire of cysteine-rich surface proteins involved in antigenic variation. Different to G. intestinalis, G. muris maintains tandem arrays of pseudogenized surface antigens at the telomeres, whereas intact surface antigens are present centrally in the chromosomes. The two classes of surface antigens engage in genetic exchange. Reconstruction of metabolic pathways from the G. muris genome suggest significant metabolic differences to G. intestinalis. Additionally, G. muris encodes proteins that might be used to modulate the prokaryotic microbiota. The responsible genes have been introduced in the Giardia genus via lateral gene transfer from prokaryotic sources. Our findings point to important evolutionary steps in the Giardia genus as it adapted to different hosts and it provides a powerful foundation for mechanistic exploration of host–pathogen interaction in the G. muris–mouse pathosystem.

中文翻译：

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鼠贾第鞭毛虫的紧凑基因组揭示了肠道原生动物寄生虫进化的重要步骤。


贾第鞭毛虫属的双胞寄生虫已经适应了不同宿主的定殖，尤其是哺乳动物的肠道。人们在基因组和基因表达水平上对人类致病性贾第鞭毛虫物种（肠贾第鞭毛虫）进行了广泛的研究，但没有其他贾第虫物种的此类信息。比较数据对于鼠贾第鞭毛虫特别有价值，它在小鼠中定殖，通常用作研究宿主对肠道寄生虫感染的反应的原型体内模型。在这里，我们报告了G. muris的基因组草案。我们发现了一个高度精简的基因组，是有史以来编码最密集的核真核基因组之一。 G. muris和G. Enteris有许多已知或预测的毒力因子，包括半胱氨酸蛋白酶和大量参与抗原变异的富含半胱氨酸的表面蛋白。与肠粘膜虫不同，鼠粘虫在端粒处维持假源化表面抗原的串联阵列，而完整的表面抗原存在于染色体的中央。两类表面抗原参与遗传交换。从G. muris基因组中重建代谢途径表明 G. muris 与G. Enteris存在显着的代谢差异。此外， G. muris编码的蛋白质可用于调节原核微生物群。相关基因已通过原核来源的横向基因转移引入贾第鞭毛虫属。 我们的研究结果指出了贾第鞭毛虫属在适应不同宿主时的重要进化步骤，并为探索贾第鞭毛虫- 小鼠病理系统中宿主 - 病原体相互作用的机制提供了强有力的基础。