Molecular Characterisation of Euryarchaeotal Community Within an Anaerobic Digester

Two euryarchaeota-specific 16S rRNA gene clone libraries (MT1 and MT2) and two bacterial 16S rRNA gene clone libraries (HW1 and HW2) were constructed using DNA isolated from two sludge samples (sample 1 and sample 2) collected from two separate tanks of commercial biogas plant operating at the methanogenesis stage, each receiving the same feedstock, after heat pretreatment for an hour at 70 °C, located near Holsworthy, Devon, UK. In the euryarchaeotal-based libraries, both samples revealed clone sequenses assigned to Methanomicrobiales and Methanosarcinales of the phylum Euryarchaeota. Although not much difference was observed in the Archaeal diversity, phylogenetic tree analysis demonstrates that 25 % of clone sequences of sample 1 and 42 % of clone sequences of sample 2 formed separate clades from cultured diversity. 16S rRNA gene-based bacterial libraries also revealed the ubiquitous presence of phyla Firmicutes and Proteobacteria. Cellulolytic bacterial clone sequences were abundant in both the samples. Fluorescent in situ hybridisation (FISH) results also revealed the presence of Methanomicrobiales and Methanosarcinales as a dominant group.