Effect of the Earthworms Lumbricus terrestris and Aporrectodea caliginosa on Bacterial Diversity in Soil

Abstract

Earthworms ingest large amounts of soil and have the potential to radically alter the biomass, activity, and structure of the soil microbial community. In this study, the diversity of eight bacterial groups from fresh soil, gut, and casts of the earthworms Lumbricus terrestris and Aporrectodea caliginosa were studied by single-strand conformation polymorphism (SSCP) analysis using both newly designed 16S rRNA gene-specific primer sets targeting Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, Deltaproteobacteria, Bacteroidetes, Verrucomicrobia, Planctomycetes, and Firmicutes and a conventional universal primer set for SSCP, with RNA and DNA as templates. In parallel, the study of the relative abundance of these taxonomic groups in the same samples was performed using fluorescence in situ hybridization. Bacteroidetes, Alphaproteobacteria, and Betaproteobacteria were predominant in communities from the soil and worm cast samples. Representatives of classes Flavobacteria and Sphingobacteria (Bacteroidetes) and Pseudomonas spp. (low-abundant Gammaproteobacteria) were detected in soil and worm cast samples with conventional and taxon-targeting SSCP and through the sequence analysis of 16S rRNA clone libraries. Physiologically active unclassified Sphingomonadaceae (Alphaproteobacteria) and Alcaligenes spp. (Betaproteobacteria) also maintained their diversities during transit through the earthworm intestine and were found on taxon-targeting SSCP profiles from the soil and worm cast samples. In conclusion, our results suggest that some specific bacterial taxonomic groups maintain their diversity and even increase their relative numbers during transit through the gastrointestinal tract of earthworms.

Diversity of Glycosyl Hydrolases from Cellulose-Depleting Communities Enriched from Casts of Two Earthworm Species

“…(most abundant in both clone libraries), and some other proteobacteria, (ii) bacterivorous protists, (iii) bacteria capable of symbiosis with protists, e.g., Legionellarelated organisms, and (iv) quite surprisingly, highly diverse verrucomicrobia, planctomycetes, stramenopiles, and other microbes probably consuming products from fermentative processes. Previously we observed that cellvibrios were rather diverse in the soil substratum and enigmatic in the casts (54). Their abundance in cultures could indicate an ability to transiently flourish and quickly colonize cellulosic substrates upon their release with the cast.…”

Effect of Earthworm Feeding Guilds on Ingested Dissimilatory Nitrate Reducers and Denitrifiers in the Alimentary Canal of the Earthworm

“…Mycobacteriumrelated narG sequences have been retrieved from soil (14,49), species of Mycobacterium can reduce nitrate to nitrite (73), and mycobacterial species and other Actinobacteria occur in earthworm guts and casts and might be associated with gut walls (9,23,24,37,69). Furthermore, the percentages of Actinobacteriarelated 16S rRNA genes can be higher in earthworm gut and cast than in soil (24,47) (41), but the nitrate reductase encoded by this operon might also dissimilate nitrate (63,73). The detection of Mycobacterium-related narG transcripts in the earthworm gut and wet, uppermost soil suggests that the encoded nitrate reductase is important for the dissimilation and/or assimilation of nitrate.…”

Methanogenic food web in the gut contents of methane-emitting earthwormEudrilus eugeniaefrom Brazil

“…However, the propensity of earthworms to consume and transform their habitat has significant impact on terrestrial ecosystems and soil processes (Darwin, 1881;Lee, 1985;Edwards and Bohlen, 1996;Makeschin, 1997;Brown and James, 2006;Nechitaylo et al, 2010). For example, Lumbricus terrestris can consume the entire annual litter fall (300 g m À 2 ) of forests it inhabits (Satchell, 1967).…”