Lloyd David, Williams Catrin F
School of Biosciences, Cardiff University, Main Building, Museum Avenue, Cathays Park, Cardiff CF10 3AT, Wales, UK.
Cultech Ltd., Unit 3, Christchurch Road, Baglan Industrial Park, Port Talbot, West Glamorgan, SA12 7BZ Wales, UK.
Mol Biochem Parasitol. 2014 Oct;197(1-2):43-9. doi: 10.1016/j.molbiopara.2014.10.002. Epub 2014 Oct 16.
The diplomonad genera are here represented by three highly diverse species, both free-living (Hexamita inflata), and parasitic (Spironucleus vortens and Giardia intestinalis). All three are moderately aerotolerant flagellates, inhabiting environments where O2 tensions are low and fluctuating. Many diplomonads are opportunistic pathogens of avian, terrestrial and aquatic animals. Hexamitids inhabit deep waters and sediments of lakes and marine basins, S. vortens commonly infects the intestinal tract of ornamental fish, particularly of cichlids and cyprinids, and G. intestinalis, the upper intestinal tracts of humans as well as domestic and farm animals. Despite these very different habitats, their known physiological and biochemical characteristics are similar, but they do differ in significant respects as their lifestyles and life cycles demand. They have efficient O2 scavenging systems, and are highly effective at countering rapid O2 fluctuations, or clustering away from its source (except for G. intestinalis when attached to the jejunal villi). Their core metabolic pathways (glycolysis using pyrophosphate), incomplete tricarboxylic acid cycle (lacking α-ketoglutarate dehydrogenase), and amino acid metabolism (with an alternative energy-generating arginine dihydrolase pathway as a possibility in some cases), largely conform to those of other protists inhabiting low-O2 environments. Mitochondrial evolutionary reduction to give hydrogenosomes as seen in Spironucleus spp. has proceeded further to its minimal state in the mitosomes of G. intestinalis. Understanding of essential redox reactions and the maintentence of redox state, especially in the infective encysted stage of G. intestinalis provide increasing possibilities for parasite control. To this aim a plethora of new synthetic chemicals and natural products (especially those from garlic, Allium sativum) show promise as replacements for the highly effective (but potentially toxic to higher organisms) 5-nitroimidazoles (e.g., metronidazole) in the treatment and/or prevention of dimplomonad infection in humans and animals.
双滴虫属在这里由三个高度多样化的物种代表，既有自由生活的（膨胀六鞭毛虫），也有寄生的（旋核鞭毛虫和肠贾第虫）。这三种都是中等耐氧的鞭毛虫，栖息在氧气张力低且波动的环境中。许多双滴虫是鸟类、陆生和水生动物的机会性病原体。六鞭毛虫栖息在湖泊和海洋盆地的深水和沉积物中，旋核鞭毛虫通常感染观赏鱼的肠道，特别是丽鱼科和鲤科鱼类，而肠贾第虫则感染人类以及家畜和农场动物的上肠道。尽管它们的栖息地差异很大，但它们已知的生理和生化特征相似，但由于它们的生活方式和生命周期的需求，它们在重要方面确实存在差异。它们有高效的氧气清除系统，在应对快速的氧气波动或远离氧气源聚集方面非常有效（肠贾第虫附着在空肠绒毛上时除外）。它们的核心代谢途径（使用焦磷酸的糖酵解）、不完全三羧酸循环（缺乏α-酮戊二酸脱氢酶）和氨基酸代谢（在某些情况下可能有替代的产生能量的精氨酸二水解酶途径），在很大程度上与其他栖息在低氧环境中的原生生物一致。线粒体进化退化产生氢化酶体，如在旋核鞭毛虫属中所见，在肠贾第虫的微小体中进一步发展到了最小状态。对基本氧化还原反应以及氧化还原状态维持的理解，特别是在肠贾第虫的感染性包囊阶段，为寄生虫控制提供了越来越多的可能性。为了这个目标，大量新的合成化学品和天然产物（特别是来自大蒜的那些）显示出有望替代高效（但对高等生物可能有毒）的5-硝基咪唑类药物（如甲硝唑），用于治疗和/或预防人和动物的双滴虫感染。
