Peroxisomes perform various metabolic processes that are primarily related to the elimination of reactive oxygen species and oxidative lipid metabolism. These organelles are present in all major eukaryotic lineages, nevertheless, information regarding the presence of peroxisomes in opportunistic parasitic protozoa is scarce and in many cases it is still unknown whether these organisms have peroxisomes at all. Here, we performed ultrastructural, cytochemical, and bioinformatic studies to investigate the presence of peroxisomes in three genera of free-living amoebae from two different taxonomic groups that are known to cause fatal infections in humans. By transmission electron microscopy, round structures with a granular content limited by a single membrane were observed in Acanthamoeba castellanii, Acanthamoeba griffini, Acanthamoeba polyphaga, Acanthamoeba royreba, Balamuthia mandrillaris (Amoebozoa), and Naegleria fowleri (Heterolobosea). Further confirmation for the presence of peroxisomes was obtained by treating trophozoites in situ with diaminobenzidine and hydrogen peroxide, which showed positive reaction products for the presence of catalase. We then performed comparative genomic analyses to identify predicted peroxin homologues in these organisms. Our results demonstrate that a complete set of peroxins—which are essential for peroxisome biogenesis, proliferation, and protein import—are present in all of these amoebae. Likewise, our in silico analyses allowed us to identify a complete set of peroxins in Naegleria lovaniensis and three novel peroxin homologues in Naegleria gruberi. Thus, our results indicate that peroxisomes are present in these three genera of free-living amoebae and that they have a similar peroxin complement despite belonging to different evolutionary lineages.

中文翻译：

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三个致病性自由生活变形虫属中过氧化物酶体的超微结构、细胞化学和比较基因组证据，包括异叶变形虫中存在这种细胞器的第一个形态学数据。

过氧化物酶体执行各种代谢过程，主要与活性氧的消除和氧化脂质代谢相关。这些细胞器存在于所有主要的真核细胞谱系中，然而，关于机会性寄生原生动物中是否存在过氧化物酶体的信息很少，并且在许多情况下，仍然不清楚这些生物体是否具有过氧化物酶体。在这里，我们进行了超微结构、细胞化学和生物信息学研究，以调查来自两个不同分类群的三个自由生活变形虫属中过氧化物酶体的存在，这些变形虫已知会导致人类致命感染。通过透射电子显微镜，在卡斯氏棘阿米巴( Acanthamoebacastellanii)、格氏棘阿米巴 ( Acanthamoeba griffini )、多食棘阿米巴 ( Acanthamoeba polyphaga)、罗伊巴棘阿米巴 ( Acanthamoeba royreba ) 、Balamuthia mandrillaris (Amoebozoa) 和Naegleria fowleri (Heterolobosea) 中观察到颗粒含量受单膜限制的圆形结构。通过用二氨基联苯胺和过氧化氢原位处理滋养体，进一步证实了过氧化物酶体的存在，这显示出过氧化氢酶存在的阳性反应产物。然后，我们进行了比较基因组分析，以确定这些生物体中预测的过氧化物酶同源物。我们的结果表明，所有这些变形虫中都存在一整套过氧化物酶，它们对于过氧化物酶体的生物发生、增殖和蛋白质输入至关重要。同样，我们的计算机分析使我们能够鉴定洛瓦耐格里球菌中的一整套过氧化物酶和格鲁伯耐格里球菌中的三种新的过氧化物酶同系物。因此，我们的结果表明，过氧化物酶体存在于这三个独立生活的变形虫属中，并且尽管它们属于不同的进化谱系，但它们具有相似的过氧化物酶补体。