| Wüst, PK; Horn, MA; Drake, HL: Clostridiaceae and Enterobacteriaceae as active fermenters in earthworm gut content, ISME Journal, 5, 92-106 (2011) | |
| Abstract: The earthworm gut provides ideal in situ conditions for ingested heterotrophic soil bacteria capable of anaerobiosis. High amounts of mucus- and plant-derived saccharides such as glucose are abundant in the earthworm alimentary canal, and high concentrations of molecular hydrogen (H2) and organic acids in the alimentary canal are indicative of ongoing fermentations. Thus, the central objective of this study was to resolve potential links between fermentations and active fermenters in gut content of the anecic earthworm Lumbricus terrestris by 16S rRNA-based stable isotope probing (SIP) with [13C]glucose as a model substrate. Glucose consumption in anoxic gut content microcosms was rapid and yielded soluble organic compounds (acetate, butyrate, formate, lactate, propionate, succinate, and ethanol) and gases (carbon dioxide and H2), products indicative of diverse fermentations in the alimentary canal. Clostridiaceae and Enterobacteriaceae were utilizers of glucose-derived carbon. Based on the detection of 16S rRNA, active phyla in gut contents included Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria, Firmicutes, Gemmatimonadetes, Nitrospirae, Planctomycetes, Proteobacteria, Tenericutes, and Verrucomicrobia, taxa common to soils. Based on a 16S rRNA gene similarity cutoff of 87.5%, 82 families were detected, 17 of which were novel family-level groups. These findings (a) illustrate the large diversity of soil taxa that might be active during gut passage, (b) demonstrate that Clostridiaceae and Enterobacteriaceae (fermentative subsets of these taxa) are selectively stimulated by glucose and might therefore be capable of consuming mucus- and plant-derived saccharides during gut passage, and (c) indicate that ingested obligate anaerobes and facultative aerobes from soil can concomitantly metabolize the same source of carbon. |
