Molecular profiling of 16S rRNA genes reveals diet-related differences of microbial communities in soil, gut, and casts of Lumbricus terrestris L. (Oligochaeta: Lumbricidae)

Abstract

Earthworms are important members of the soil macrofauna. They modify soil physical properties, soil organic matter decomposition, and thus regulate carbon and nitrogen cycling in soil. However, their interactions with soil microorganisms are still poorly understood, in particular the effect of gut passage on the community structure of ingested microorganisms. Moreover, it is still unsolved, if earthworms, like many other soil-feeding invertebrates, possess an indigenous gut microbial community. Therefore, we investigated the bacterial and archaeal community structure in soil (with and without additional beech litter), gut, and fresh casts of Lumbricus terrestris, an anecic litter-feeding earthworm, by means of terminal-restriction fragment length polymorphism (T-RFLP) analysis of 16S rRNA gene fragments. Ecological indices of community diversity and similarity, calculated from the T-RFLP profiles, revealed only small differences between the bacterial and archaeal communities in soil, gut, and fresh casts under both feeding conditions, especially in comparison to other soil-feeding invertebrates. However, multivariate statistical analysis combining multidimensional scaling and discriminant function analysis proved that these differences were highly significant, in particular when the earthworms were fed beech litter in addition. Because there were no dominant gut-specific OTUs detectable, the existence of an abundant indigenous earthworm microbial community appears unlikely, at least in the midgut region of L. terrestris.

Structure and Topology of Microbial Communities in the Major Gut Compartments ofMelolontha melolonthaLarvae (Coleoptera: Scarabaeidae)

“…DNA was extracted and purified from gut samples and food plant roots as previously described (20). 16S rRNA genes were amplified using primers 27f and 907r (37) or Ar109f and Ar915r for bacterial and archaeal clone libraries, as described elsewhere in detail (19,20). The apsA gene encoding the ␣ subunit of the adenosine-5Ј-phosphosulfate (APS) reductase of sulfate-reducing bacteria (SRB) was amplified with the primers APS7-F and APS8-R as described elsewhere (22), except that 1 l of a 1:20 dilution of DNA extract was added as a template and a thermal PCR profile with 35 cycles at an annealing temperature of 52°C was used.…”

“…The bacterial species richness of the hindgut lumen and hindgut wall was calculated using Chao1 as a nonparametric estimator (20). T-RFLP profiles were normalized, and the diversity (Shannon-Wiener index), evenness, and community similarity (Morisita) indices were calculated as described elsewhere (19). Differences between samples (in ecological indices, physicochemical parameters, or FISH cell counts) were checked for statistical significance (P Յ 0.05) with nonparametric MannWhitney tests using SYSTAT 10.0 (SPSS Inc., Chicago, Ill.).…”

Differences between Bacterial Communities in the Gut of a Soil-Feeding Termite (Cubitermes niokoloensis) and Its Mounds

“…For this reason, termite mounds are a major functional compartment in tropical soils (2), comparable to the drilosphere created by earthworms, which can modify the activity and diversity of microbial soil communities (25). However, although the relationship between earthworm casts and microorganism structures in soil has been well characterized (10), this relationship has not yet been determined for bacterial communities in termite constructions.…”

Selective recruitment of bacteria during embryogenesis of an earthworm

“…The Lumbricid earthworms (members of the family Lumbricidae), commonly found in North America and Europe, alter soil texture and chemical composition on a large scale due to the combined activity of both worm and bacteria (Darwin, 1889;Furlong et al, 2002;Horn et al, 2003;Ihssen et al, 2003;Edwards, 2004;Egert et al, 2004). The gut community essentially consists of ingested bacteria from the soil, which then shifts in composition in response to the earthworm gut conditions.…”