Emission of nitrous oxide and dinitrogen by diverse earthworm families from Brazil and resolution of associated denitrifying and nitrate-dissimilating taxa

Abstract

The anoxic earthworm gut augments the activity of ingested microorganisms capable of anaerobiosis. Small earthworms (Lumbricidae) emit denitrification-derived N2O, whereas the large Octochaetus multiporus (Megascolecidae) does not. To examine this paradox, differently sized species of the families Glossoscolecidae (Rhinodrilus, Glossoscolex, Pontoscolex), Megascolecidae (Amynthas, Perionyx), Acanthodrilidae (Dichogaster), and Eudrilidae (Eudrilus) from Brazil were analyzed. Small species and the large Rhinodrilus alatus emitted N2O, whereas the large Glossoscolex paulistus did not, even though its gut could denitrify. N2 and N2O were emitted concomitantly, and R. alatus emitted the highest amount of N2. Denitrifiers and dissimilatory nitrate reducers were analyzed by barcoded amplicon pyrosequencing of narG, nirK, and nosZ. Gene sequences in gut and soil of the large G. paulistus were similar, whereas sequences in gut and soil of the small Amynthas gracilis were different and were also different compared with those of the gut and soil of G. paulistus. However, the denitrifying gut microbiota for both earthworms appeared to be soil-derived and dominated by Rhizobiales. The results demonstrated that (1) the emission of denitrification-derived N2O is widespread in different earthworm families, (2) large earthworms can also emit nitrogenous gases, and (3) ingested members of Rhizobiales are associated with this emission. © 2012 Federation of European Microbiological Societies.