Depkat-Jakob, PS; Hilgarth, M; Horn, MA; Drake, HL: Effect of Earthworm Feeding Guild on Ingested Dissimilatory Nitrate Reducers and Denitrifiers in the Alimentary Canal of the Earthworm, Applied and Environmental Microbiology, Vol. 76(18), 6205-6214 (2010)
The earthworm gut is an anoxic nitrous oxide (N2O)-emitting microzone in aerated soils. In situ conditions of the gut might stimulate ingested nitrate-reducing soil bacteria linked to this emission. The objective of this study was to determine if dissimilatory nitrate reducers and denitrifiers in the alimentary canal were affected by feeding guilds (epigeic [Lumbricus rubellus], anecic [Lumbricus terrestris], and endogeic [Aporrectodea caliginosa]). Genes and gene transcripts of narG (encodes for a subunit of nitrate reductase and targets both dissimilatory nitrate reducers and denitrifiers) and nosZ (encodes for a subunit of N2O reductase and targets denitrifiers) were detected in guts and soils. Gut derived sequences were similar to those of cultured and uncultured soil bacteria, and also to soil derived sequences obtained in this study. Gut derived narG sequences and narG terminal restriction fragments (TRFs) were mainly affiliated with gram positive organisms (Actinobacteria). The majority of gut and uppermost soil derived narG transcripts affiliated with Mycobacterium (Actinobacteria). In contrast, narG sequences indicative of gram negatives (Proteobacteria) were dominant in mineral soil. Most nosZ sequences and nosZ TRFs were affiliated with Bradyrhizobium (Alphaproteobacteria) and uncultured soil bacteria. TRF profiles indicated that nosZ transcripts were more affected by earthworm feeding guilds than were nosZs, whereas narG transcripts were less affected by earthworm feeding guilds than were narGs. narG and nosZ transcripts were different and less diverse in the earthworm gut than in mineral soil. The collective results indicated that dissimilatory nitrate reducers and denitrifiers in the earthworm gut were soil derived and that ingested narG- and nosZ-containing taxa were not uniformly stimulated in the guts of worms from different feeding guilds
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