Functional bacterial and archaeal community structures of major trophic groups in a full-scale anaerobic sludge digester

Functional Bacteria and Archaea community structures of a full-scale anaerobic sludge digester were investigated by using a full-cycle 16S rRNA approach followed by microautoradiography (MAR)–fluorescent in situ hybridization (FISH) technique and micromanipulation. FISH analysis with a comprehensive set of 16S and 23S rRNA-targeted oligonucleotide probes based on 16S rRNA clone libraries revealed that the Gram-positive bacteria represented by probe HGC69A-hybridized Actinobacteria (8.5±1.4% of total 4′, 6-diamidino-2-phenylindole (DAPI)-stained cells) and probe LGC354-hybridized Firmicutes (3.8±0.8%) were the major phylogenetic bacterial phyla, followed by Bacteroidetes (4.0±1.2%) and Chloroflexi (3.7±0.8%). The probe MX825-hybridized Methanosaeta (7.6±0.8%) was the most abundant archaeal group, followed by Methanomicrobiales (2.8±0.6%) and Methanobacteriaceae (2.7±0.4%). The functional community structures (diversity and relative abundance) of major trophic groups were quantitatively analyzed by MAR–FISH. The results revealed that glucose-degrading microbial community had higher abundance (ca. 10.6±4.9% of total DAPI-stained cells) and diversity (at least seven phylogenetic groups) as compared with fatty acid-utilizing microbial communities, which were more specialized to a few phylogenetic groups. Despite the dominance of Betaproteobacteria, members of Chloroflexi, Smithella, Syntrophomonas and Methanosaeta groups dominated the [14C]glucose-, [14C]propionate-, [14C]butyrate- and [14C]acetate-utilizing microorganism community, and accounted for 27.7±4.3%, 29.6±7.0%, 34.5±7.6% and 18.2±9.5%, respectively. In spite of low abundance (ca. 1%), the hitherto unknown metabolic functions of Spirochaeta and candidate phylum of TM7 as well as Synergistes were found to be glucose and acetate utilization, respectively.