Gut wall bacteria of earthworms: a natural selection process

Abstract

Earthworms and microorganisms are interdependent and their interactions regulate the biogeochemistry of terrestrial soils. Investigating earthworm-microorganism interactions, we tested the hypothesis that differences in burrowing and feeding habits of anecic and endogeic earthworms are reflected by the existence of ecological group-specific gut wall bacterial communities. Bacterial community was detected using automated ribosomal intergenic spacer analysis of 16S and 23S genes and ribotype data was used to assess diversity and community composition. Using soil and earthworm samples collected from adjacent wheat-barley and grass-clover fields, we found that the anecic Lumbricus terrestris and L. friendi, the endogeic Aporrectodea caliginosa and A. longa (classically defined as anecic, but now known to possess endogeic characteristics) contain ecological group-specific gut wall-associated bacterial communities. The abundance of specific gut wall-associated bacteria (identified by sequence analysis of ribotype bands), including Proteobacteria, Firmicutes and an actinobacterium, was ecological group dependent. A microcosm study, conducted using A. caliginosa and L. terrestris and five different feeding regimes, indicated that food resource can cause shifts in gut wall-associated bacterial community, but the magnitude of these shifts did not obscure the delineation between ecological group specificity. Using A. caliginosa and A. longa samples collected in six different arable fields, we deduced that, within an ecological group, habitat was a more important determinant of gut wall-associated bacterial community composition than was host species. Hence, we conclude that the selection of bacteria associated with the gut wall of earthworms is a natural selection process and the strongest determinant of this process is in the order ecological group4habitat4species.

Organic matter composition and the protist and nematode communities around anecic earthworm burrows

“…In fact, although soil is a highly heterogeneous environment where competing species may co-occur at small scales (Amarasekare 2003)-the so-called enigma of soil animal diversity (Anderson 1975)-trait differences between cooccurring anecic earthworm species have been found. In particular, A. longa feeds more extensively on highly mineralized SOM than do Lumbricus spp., the latter showing a stronger preference for fresher detritus (Briones et al 2005;Thakuria et al 2010). Also, the burrowing behaviour of A. longa appears somewhat intermediate between that of endogeic earthworms, which dig transient channels below the soil surface, and true anecic earthworms (Bastardie et al 2005).…”

“…Also, the burrowing behaviour of A. longa appears somewhat intermediate between that of endogeic earthworms, which dig transient channels below the soil surface, and true anecic earthworms (Bastardie et al 2005). But it should be noted that A. longa and other anecic species are remarkably flexible in their diet (Schmidt 1999;Thakuria et al 2010;Griffith et al 2013), as they tune their behaviour according to environmental conditions (e.g. availability of surface residues).…”

Elucidating the microbial community associated with the protein preference of sludge-degrading worms

“…Thakuria et al [25] found that differences in substrate composition can result in microbial shifts of the gut wall-associated bacteria. However, the strongest determinant in the selection process of the gut wall-associated bacteria is the ecological group (anecic or endogeic) followed by the habitat the host occupies and lastly the species of earthworm.…”

“…These microbial changes are probably not only due to the worms' removal or consumption of bacteria and the excretion of degradation products, but also due to the type of substrate the worms consume [25]. In turn, these environmental changes could result in optimised growth conditions for specific bacterial species associated with the worms.…”

Enumeration of Gut Bacterial Population in Eisenia fetida Exposed to Chlorpyrifos

“…As they are abundant in number and highly productive species, so they are keystone species in the food web of soil environment (Thakuria et al, 2010). Earthworm burrows and drilosphere act as microhabitats for soil invertebrates like nematodes (Andriuzzi et al, 2016), arthropods (Boivin et al, 2006).…”