背景:许多节肢动物依靠他们的肠道微生物组来消化植物材料,通常氮含量低,但复杂多糖含量高。Detritivores,比如千足虫,过着特别糟糕的饮食,但是他们的微生物组的身份和营养贡献在很大程度上是未知的。在这项研究中,热带千足虫Epiboluspulchripes的后肠微生物群(大,甲烷排放)和温带千足虫Glomerisconnexa(小,非甲烷排放),以相同的饮食为食,使用比较宏基因组学和超转录组学进行了研究。
结果:结果表明,E.pulchripes中的微生物负荷比G.connexa中的微生物负荷高得多,并且更加多样化。这两个物种的微生物群落差异很大,在G.connexa中,拟杆菌主要是E.pulchripes和变形杆菌(Pseudomonadota)的后肠。尽管同样的测序努力,从头组装和分箱回收了282个来自E.pulchripes的宏基因组组装基因组(MAG)和来自G.Connexa的33个,包括90个新的细菌类群(81个在E.pulchripes和9个在G.connexa)。然而,尽管有这种分类差异,大部分功能,包括碳水化合物水解,硫酸盐还原,和氮循环,是两个物种共有的。拟杆菌(Bacteroidetes)的成员是E.pulchripes中复杂碳降解的主要因子,而变形杆菌的成员在G.connexa占主导地位。脱硫细菌的成员是E.pulchripes中潜在的硫酸盐还原细菌。在放线菌群中发现了异化硝酸盐还原的能力(E.pulchripes)和变形杆菌(两种),但只有变形杆菌具有反硝化能力(两种)。相比之下,一些功能只在E.pulchripes中发现。这些包括还原性乙酸生成,在E.pulchripes的脱硫杆菌和Firmicutes(Bacillota)成员中发现。此外,重氮生物仅在E.pulchripes中发现,Firmicutes和Proteobacteria的一些成员表达nifH基因。有趣的是,真菌细胞壁降解糖苷水解酶(GHs)是在两种千足虫物种中表达的最丰富的碳水化合物活性酶(CAZymes)之一。这表明真菌生物质在千足虫饮食中起着重要作用。
结论:总体而言,这些结果为千足虫后肠微生物群落的基因组能力提供了详细的见解,并阐明了这些必需有害微生物的生态生理学。视频摘要。
BACKGROUND: Many arthropods rely on their gut microbiome to digest plant material, which is often low in nitrogen but high in complex polysaccharides. Detritivores, such as millipedes, live on a particularly poor diet, but the identity and nutritional contribution of their microbiome are largely unknown. In this study, the hindgut microbiota of the tropical millipede Epibolus pulchripes (large, methane emitting) and the temperate millipede Glomeris connexa (small, non-methane emitting), fed on an identical diet, were studied using comparative metagenomics and metatranscriptomics.
RESULTS: The results showed that the microbial load in E. pulchripes is much higher and more diverse than in G. connexa. The microbial communities of the two species differed significantly, with Bacteroidota dominating the hindguts of E. pulchripes and Proteobacteria (Pseudomonadota) in G. connexa. Despite equal sequencing effort, de novo assembly and binning recovered 282 metagenome-assembled genomes (MAGs) from E. pulchripes and 33 from G. connexa, including 90 novel bacterial taxa (81 in E. pulchripes and 9 in G. connexa). However, despite this taxonomic divergence, most of the functions, including carbohydrate hydrolysis, sulfate reduction, and nitrogen cycling, were common to the two species. Members of the Bacteroidota (Bacteroidetes) were the primary agents of complex carbon degradation in E. pulchripes, while members of Proteobacteria dominated in G. connexa. Members of Desulfobacterota were the potential sulfate-reducing bacteria in E. pulchripes. The capacity for dissimilatory nitrate reduction was found in Actinobacteriota (E. pulchripes) and Proteobacteria (both species), but only Proteobacteria possessed the capacity for denitrification (both species). In contrast, some functions were only found in E. pulchripes. These include reductive acetogenesis, found in members of Desulfobacterota and Firmicutes (Bacillota) in E. pulchripes. Also, diazotrophs were only found in E. pulchripes, with a few members of the Firmicutes and Proteobacteria expressing the nifH gene. Interestingly, fungal-cell-wall-degrading glycoside hydrolases (GHs) were among the most abundant carbohydrate-active enzymes (CAZymes) expressed in both millipede species, suggesting that fungal biomass plays an important role in the millipede diet.
CONCLUSIONS: Overall, these results provide detailed insights into the genomic capabilities of the microbial community in the hindgut of millipedes and shed light on the ecophysiology of these essential detritivores. Video Abstract.