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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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（Giardia）的双文凭寄生虫已经适应了不同宿主的定殖，最显着的是哺乳动物的肠道。人类致病性贾第鞭毛虫种贾第鞭毛虫已经在基因组和基因表达水平上进行了广泛的研究，但是其他贾第鞭毛虫没有这样的信息。比较数据对于鼠李木（Giardia muris）特别有价值，鼠李木定居于小鼠，通常用作研究宿主对肠道寄生虫感染反应的原型体内模型。在这里，我们报告鼠毛草的基因组草案。我们发现了高度精简的基因组，是核真核基因组中描述过的编码最密集的基因组。G.缪里斯和G.肠共享许多已知的或预测的毒力因子，包括半胱氨酸蛋白酶和大型剧目参与抗原变异富含半胱氨酸的表面蛋白。与肠小肠结肠菌不同，穆勒氏菌在端粒处保持串联的假基因表面抗原串联排列，而完整的表面抗原集中存在于染色体中。这两类表面抗原参与基因交换。穆里斯氏菌基因组代谢途径的重建表明与肠道小肠菌有明显的代谢差异。另外，鼠疫杆菌编码可用于调节原核微生物群的蛋白质。负责任的基因已通过原核生物的侧向基因转移被引入到贾第鞭毛虫属中。我们的发现指出了贾第鞭毛虫属的重要进化步骤，因为它适应了不同的宿主，并且为机理探索了鼠李-小鼠病理系统中宿主-病原体相互作用提供了有力的基础。