454 pyrosequencing analyses of bacterial and archaeal richness in 21 full-scale biogas digesters

TLDR

The microbial community of 21 full‑scale biogas reactors was examined using 454 pyrosequencing of 16S rRNA gene sequences, covering seven sewage‑sludge and fourteen codigester reactors of mesophilic and thermophilic conditions. Pyrosequencing yielded over 160,000 sequences spanning 11 phyla, 23 classes, and 95 genera, with bacteria more abundant and diverse than archaea; sewage‑sludge reactors were dominated by Actinobacteria, Proteobacteria, Chloroflexi, Spirochetes, and Euryarchaeota, while codigesters were dominated by Firmicutes, acetoclastic methanogens were present only in sewage‑sludge reactors, suggesting acetate‑derived methane in codigesters occurs mainly via syntrophic oxidation, and principal component analysis grouped reactors by substrate and temperature.

Abstract

The microbial community of 21 full-scale biogas reactors was examined using 454 pyrosequencing of 16S rRNA gene sequences. These reactors included seven (six mesophilic and one thermophilic) digesting sewage sludge (SS) and 14 (ten mesophilic and four thermophilic) codigesting (CD) various combinations of wastes from slaughterhouses, restaurants, households, etc. The pyrosequencing generated more than 160000 sequences representing 11 phyla, 23 classes, and 95 genera of Bacteria and Archaea. The bacterial community was always both more abundant and more diverse than the archaeal community. At the phylum level, the foremost populations in the SS reactors included Actinobacteria, Proteobacteria, Chloroflexi, Spirochetes, and Euryarchaeota, while Firmicutes was the most prevalent in the CD reactors. The main bacterial class in all reactors was Clostridia. Acetoclastic methanogens were detected in the SS, but not in the CD reactors. Their absence suggests that methane formation from acetate takes place mainly via syntrophic acetate oxidation in the CD reactors. A principal component analysis of the communities at genus level revealed three clusters: SS reactors, mesophilic CD reactors (including one thermophilic CD and one SS), and thermophilic CD reactors. Thus, the microbial composition was mainly governed by the substrate differences and the process temperature.