Department of Ecological Microbiology, University of Bayreuth, Bayreuth, Germany.
Department of Ecological Microbiology, University of Bayreuth, Bayreuth, Germany
Appl Environ Microbiol. 2018 May 17;84(11). doi: 10.1128/AEM.00657-18. Print 2018 Jun 1.
Earthworms are a dominant macrofauna in soil ecosystems and have determinative effects on soil fertility and plant growth. These invertebrates feed on ingested material, and gizzard-linked disruption of ingested fungal and bacterial cells is conceived to provide diverse biopolymers in the anoxic alimentary canals of earthworms. Fermentation in the gut is likely important to the utilization of ingested biopolymer-derived compounds by the earthworm. This study therefore examined the fermentative responses of gut content-associated microbes of the model earthworm to (i) microbial cell lysate (to simulate gizzard-disrupted cells) and (ii) dominant biopolymers of such biomass, protein, and RNA. The microbial cell lysate augmented the production of H, CO, and diverse fatty acids (e.g., formate, acetate, propionate, succinate, and butyrate) in anoxic gut content microcosms, indicating that the cell lysate triggered diverse fermentations. Protein and RNA also augmented diverse fermentations in anoxic microcosms of gut contents, each yielding a distinct product profile (e.g., RNA yielded H and succinate, whereas protein did not). The combined product profile of protein and RNA treatments was similar to that of cell lysate treatments, and 16S rRNA-based analyses indicated that many taxa that responded to cell lysate were similar to taxa that responded to protein or RNA. In particular, protein stimulated , , and , whereas RNA stimulated These findings demonstrate the capacity of gut-associated obligate anaerobes and facultative aerobes to catalyze biopolymer-driven fermentations and highlight the potential importance of protein and RNA as substrates linked to the overall turnover dynamics of organic carbon in the alimentary canal of the earthworm. The subsurface lifestyle of earthworms makes them an unnoticed component of the terrestrial biosphere. However, the propensity of these invertebrates to consume their home, i.e., soil and litter, has long-term impacts on soil fertility, plant growth, and the cycling of elements. The alimentary canals of earthworms can contain up to 500 ml anoxic gut content per square meter of soil, and ingested soil may contain 10 or more microbial cells per gram dry weight, considerations that illustrate that enormous numbers of soil microbes are subject to anoxia during gut passage. Feeding introduces diverse sources of biopolymers to the gut, and the gut fermentation of biopolymers could be important to the transformation of matter by the earthworm and its capacity to utilize fermentation-derived fatty acids. Thus, this study examined the capacity of microbes in earthworm gut contents to ferment protein and RNA, dominant biopolymers of cells that become disrupted during gut passage.
蚯蚓是土壤生态系统中的主要大型动物，对土壤肥力和植物生长有决定性影响。这些无脊椎动物以摄入的物质为食，而胃连接的破坏被认为可以在蚯蚓缺氧的消化道中提供各种生物聚合物。肠道中的发酵可能对蚯蚓利用摄入的生物聚合物衍生化合物很重要。因此，本研究检查了模型蚯蚓肠道内容物相关微生物对（i）微生物细胞裂解物（模拟胃破坏细胞）和（ii）这种生物量的主要生物聚合物，即蛋白质和 RNA 的发酵反应。在缺氧的肠道内容物微宇宙中，微生物细胞裂解物增加了 H、CO 和各种脂肪酸（例如甲酸盐、乙酸盐、丙酸盐、琥珀酸盐和丁酸盐）的产生，表明细胞裂解物引发了各种发酵。蛋白质和 RNA 也增加了缺氧微宇宙中肠道内容物的各种发酵，每种都产生了不同的产物谱（例如，RNA 产生 H 和琥珀酸盐，而蛋白质则没有）。蛋白质和 RNA 处理的组合产物谱与细胞裂解物处理的产物谱相似，基于 16S rRNA 的分析表明，对细胞裂解物有反应的许多分类群与对蛋白质或 RNA 有反应的分类群相似。特别是，蛋白质刺激了、和，而 RNA 刺激了。这些发现证明了肠道相关专性厌氧菌和兼性需氧菌催化生物聚合物驱动发酵的能力，并强调了蛋白质和 RNA 作为与蚯蚓消化道有机碳整体周转动态相关的底物的潜在重要性。蚯蚓的地下生活方式使它们成为陆地生物圈中未被注意到的组成部分。然而，这些无脊椎动物消耗其家园（即土壤和凋落物）的倾向对土壤肥力、植物生长和元素循环有长期影响。蚯蚓的肠道内容物每平方米土壤可达 500 毫升缺氧肠道内容物，每克干重摄入的土壤可能含有 10 个或更多的微生物细胞，这表明在肠道通过时，大量的土壤微生物会缺氧。进食会向肠道中引入各种生物聚合物来源，而生物聚合物的肠道发酵对蚯蚓转化物质及其利用发酵衍生脂肪酸的能力可能很重要。因此，本研究检查了蚯蚓肠道内容物中的微生物发酵蛋白质和 RNA 的能力，这是在肠道通过过程中被破坏的细胞的主要生物聚合物。
