PDF(Pubmed)
Abstract：
Anaerobic protists frequently harbour methanogenic archaea, which apparently contribute to the hosts\' fermentative metabolism by consuming excess H2. However, the ecological properties of endosymbiotic methanogens remain elusive in many cases. Here we investigated the ecology and genome of the endosymbiotic methanogen of the Cononympha protists in the hindgut of the termite Coptotermes formosanus. Microscopic and 16S rRNA amplicon sequencing analyses revealed that a single species, designated here \"Candidatus Methanobrevibacter cononymphae\", is associated with both Cononympha leidyi and Cononympha koidzumii and that its infection rate in Cononympha cells varied from 0.0% to 99.8% among termite colonies. Fine-scale network analysis indicated that multiple 16S rRNA sequence variants coexisted within a single host cell and that identical variants were present in both Cononympha species and also on the gut wall. Thus, \"Ca. Methanobrevibacter cononymphae\" is a facultative endosymbiont, transmitted vertically with frequent exchanges with the gut environment. Indeed, transmission electron microscopy showed escape or uptake of methanogens from/by a Cononympha cell. The genome of \"Ca. Methanobrevibacter cononymphae\" showed features consistent with its facultative lifestyle: i.e., the genome size (2.7 Mbp) comparable to those of free-living relatives; the pseudogenization of the formate dehydrogenase gene fdhA, unnecessary within the non-formate-producing host cell; the dependence on abundant acetate in the host cell as an essential carbon source; and the presence of a catalase gene, required for colonization on the microoxic gut wall. Our study revealed a versatile endosymbiosis between the methanogen and protists, which may be a strategy responding to changing conditions in the termite gut.
摘要：
厌氧原生生物经常携带产甲烷古细菌，这显然有助于宿主的发酵代谢消耗过量的H2。然而,在许多情况下，内共生产甲烷菌的生态特性仍然难以捉摸。在这里，我们研究了白蚁的后肠中Cononypha原生生物的内共生产甲烷菌的生态学和基因组。显微镜和16SrRNA扩增子测序分析显示，单一物种，此处指定为“念珠菌甲氧菌”，与Cononymphaleidyi和Cononymphakoidzumii有关，并且其在Cononympha细胞中的感染率在白蚁菌落中从0.0％到99.8％不等。精细网络分析表明，多个16SrRNA序列变体共存于单个宿主细胞中，并且在Cononympha物种和肠壁中均存在相同的变体。因此，“Ca。共生体是兼性内生体，垂直传播，与肠道环境频繁交流。的确,透射电子显微镜显示产甲烷菌从Cononympha细胞逃逸或吸收。“Ca的基因组。信烯杆菌“显示出与其兼性生活方式一致的特征：即，基因组大小（2.7Mbp）与自由生活的亲戚相当；甲酸脱氢酶基因fdhA的假基因化，在非产甲酸的宿主细胞内是不必要的；依赖宿主细胞中丰富的乙酸作为必需碳源；以及过氧化氢酶基因的存在，需要在微氧肠壁上定植。我们的研究揭示了产甲烷菌和原生生物之间的多才多艺的内共生关系，这可能是一种应对白蚁肠道条件变化的策略。
