Institute of Soil Biology, Biology Centre CAS, České Budějovice, Czech Republic.
SoWa Research Infrastructure, Biology Centre CAS, České Budějovice, Czech Republic.
Appl Environ Microbiol. 2021 Jul 13;87(15):e0061421. doi: 10.1128/AEM.00614-21.
Methanogens represent the final decomposition step in anaerobic degradation of organic matter, occurring in the digestive tracts of various invertebrates. However, factors determining their community structure and activity in distinct gut sections are still debated. In this study, we focused on the tropical millipede species Archispirostreptus gigas (Diplopoda, Spirostreptidae) and Epibolus pulchripes (Diplopoda, Pachybolidae), which release considerable amounts of methane. We aimed to characterize relationships between physicochemical parameters, methane production rates, and methanogen community structure in the two major gut sections, midgut and hindgut. Microsensor measurements revealed that both sections were strictly anoxic, with reducing conditions prevailing in both millipedes. Hydrogen concentration peaked in the anterior hindgut of . In both species, the intestinal pH was significantly higher in the hindgut than in the midgut. An accumulation of acetate and formate in the gut indicated bacterial fermentation activities in the digestive tracts of both species. Phylogenetic analysis of 16S rRNA genes showed a prevalence of spp. (), accompanied by a small fraction of so-far-unclassified "" (), in both species, which suggests that methanogenesis is mostly hydrogenotrophic. We conclude that anoxic conditions, negative redox potential, and bacterial production of hydrogen and formate promote gut colonization by methanogens. The higher activities of methanogens in the hindgut are explained by the higher pH of this compartment and their association with ciliates, which are restricted to this compartment and present an additional source of methanogenic substrates. Methane (CH) is the second most important atmospheric greenhouse gas after CO and is believed to account for 17% of global warming. Methanogens are a diverse group of archaea and can be found in various anoxic habitats, including digestive tracts of plant-feeding animals. Termites, cockroaches, the larvae of scarab beetles, and millipedes are the only arthropods known to host methanogens and emit large amounts of methane. Millipedes are ranked as the third most important detritivores after termites and earthworms, and they are considered keystone species in many terrestrial ecosystems. Both methane-producing and non-methane-emitting species of millipedes have been observed, but what limits their methanogenic potential is not known. In the present study, we show that physicochemical gut conditions and the distribution of symbiotic ciliates are important factors determining CH emission in millipedes. We also found close similarities to other methane-emitting arthropods, which might be associated with their similar plant-feeding habits.
产甲烷菌是有机物质在厌氧降解过程中的最后分解步骤，存在于各种无脊椎动物的消化道中。然而，决定它们在不同肠道部位的群落结构和活性的因素仍存在争议。在这项研究中，我们专注于热带千足虫物种 Archispirostreptus gigas（多足纲，Spirastreptidae 科）和 Epibolus pulchripes（多足纲，Pachybolidae 科），它们释放出大量的甲烷。我们的目的是描述两个主要肠道部位（中肠和后肠）中的理化参数、甲烷产生速率和产甲烷菌群落结构之间的关系。微传感器测量表明，两个部位均严格缺氧，两种千足虫的还原条件均占主导地位。氢浓度在前后肠的交汇处达到峰值。在这两种物种中，肠道 pH 值在后肠显著高于中肠。肠道中乙酸盐和甲酸盐的积累表明两种物种的消化道中都存在细菌发酵活动。16S rRNA 基因的系统发育分析表明，在这两种物种中，产甲烷菌属（Methanobrevibacter）占主导地位（），其次是一小部分迄今尚未分类的“”（），这表明产甲烷作用主要是氢营养型的。我们得出的结论是，缺氧条件、负氧化还原电位以及细菌产生的氢和甲酸盐促进了产甲烷菌在肠道中的定植。后肠中产甲烷菌的活性更高，原因是该部位的 pH 值较高，并且与纤毛虫有关联，纤毛虫仅限于该部位，是产甲烷菌的另一种底物来源。甲烷（CH）是仅次于 CO 的第二大重要大气温室气体，被认为占全球变暖的 17%。产甲烷菌是一组多样化的古菌，存在于各种缺氧环境中，包括食草动物的消化道。已知只有白蚁、蟑螂、甲虫幼虫和千足虫等节肢动物宿主产甲烷菌并大量排放甲烷。千足虫是仅次于白蚁和蚯蚓的第三大重要碎屑分解者，它们被认为是许多陆地生态系统中的关键物种。已观察到产甲烷和不排放甲烷的千足虫，但限制其产甲烷能力的因素尚不清楚。在本研究中，我们表明，肠道的理化条件和共生纤毛虫的分布是决定千足虫 CH 排放的重要因素。我们还发现与其他排放甲烷的节肢动物有密切的相似性，这可能与其相似的食草习性有关。
