State Key Laboratory of Freshwater Ecology and Biotechnology, Key Laboratory of Aquaculture Disease Control, Ministry of Agriculture, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, 430072, Hubei, China.
University of Chinese Academy of Sciences, Beijing, 100049, China.
BMC Genomics. 2023 Oct 19;24(1):624. doi: 10.1186/s12864-023-09706-6.
Anaerobic parasitic ciliates are a specialized group of ciliates that are adapted to anoxic and oxygen-depleted habitats. Among them, Balantidium polyvacuolum, which inhabits the hindgut of Xenocyprinae fishes, has received very limited scientific attention, so the molecular mechanism of its adaptation to the digestive tract microenvironment is still unclear. In this study, transmission electron microscopy (TEM) and single-cell transcriptome analysis were used to uncover the metabolism of B. polyvacuolum. Starch granules, endosymbiotic bacteria, and multiple specialized mitochondrion-related organelles (MROs) of various shapes were observed. The MROs may have completely lost the electron transport chain (ETC) complexes I, III, IV, and V and only retained succinate dehydrogenase subunit A (SDHA) of complex II. The tricarboxylic acid (TCA) cycle was also incomplete. It can be inferred that the hypoxic intestinal environment has led to the specialization of the mitochondria in B. polyvacuolum. Moreover, carbohydrate-active enzymes (CAZymes), including carbohydrate esterases, enzymes with a carbohydrate-binding module, glycoside hydrolases, and glycosyltransferases, were identified, which may constitute evidence that B. polyvacuolum is able to digest carbohydrates and starch. These findings can improve our knowledge of the energy metabolism and adaptive mechanisms of B. polyvacuolum.
厌氧寄生纤毛虫是一类适应缺氧和缺氧环境的纤毛虫，其中，栖息在鲤科鱼类后肠的多泡泡棘尾虫受到的科学关注非常有限，因此其适应消化道微环境的分子机制尚不清楚。在这项研究中，使用透射电子显微镜（TEM）和单细胞转录组分析来揭示多泡泡棘尾虫的代谢情况。观察到淀粉颗粒、内共生细菌和多种形状的多种专门的线粒体相关细胞器（MRO）。这些 MRO 可能已经完全失去了电子传递链（ETC）复合物 I、III、IV 和 V，仅保留了复合物 II 的琥珀酸脱氢酶亚基 A（SDHA）。三羧酸（TCA）循环也不完整。可以推断，缺氧的肠道环境导致了多泡泡棘尾虫的线粒体特化。此外，还鉴定出了碳水化合物活性酶（CAZymes），包括碳水化合物酯酶、具有碳水化合物结合模块的酶、糖苷水解酶和糖基转移酶，这可能构成了多泡泡棘尾虫能够消化碳水化合物和淀粉的证据。这些发现可以提高我们对多泡泡棘尾虫能量代谢和适应机制的认识。
