Identification of putative methylotrophic and hydrogenotrophic methanogens within sedimenting material and copepod faecal pellets

In the present study, sedimenting particulate material and faecal pellets from natural and laboratory-reared copepods were examined for the presence of methanogenic Archaea. 16S rRNA gene sequences closely related to Methanogenium, Methanobacterium and Methanolobus spp. were detected, indicating the potential for different methanogenic metabolisms (hydrogenotrophic and methylotrophic methanogenesis) in these samples. The present study represents the first 16S rRNA gene-based identification of methanogens in copepod faecal pellets and importantly the first reported 16S rRNA-based occurrence of potentially hydrogenotrophic methanogens from marine particulate material, where it was previously thought that methylotrophic methanogens dominated methanogenesis. Anaerobic incubation experiments using sedimenting particulate material and copepod faecal pellets demonstrated active methane production and indicated that the associated methanogenic community was viable under the conditions tested.