title: Identification of a novel acetate-utilizing bacterium belonging to Synergistes group 4 in anaerobic digester sludge.
abstract: Major acetate-utilizing bacterial and archaeal populations in methanogenic anaerobic digester sludge were identified and quantified by radioisotope- and stable-isotope-based functional analyses, microautoradiography-fluorescence in situ hybridization (MAR-FISH) and stable-isotope probing of 16S rRNA (RNA-SIP) that can directly link 16S rRNA phylogeny with in situ metabolic function. First, MAR-FISH with (14)C-acetate indicated the significant utilization of acetate by only two major groups, unidentified bacterial cells and Methanosaeta-like filamentous archaeal cells, in the digester sludge. To identify the acetate-utilizing unidentified bacteria, RNA-SIP was conducted with (13)C(6)-glucose and (13)C(3)-propionate as sole carbon source, which were followed by phylogenetic analysis of 16S rRNA. We found that bacteria belonging to Synergistes group 4 were commonly detected in both 16S rRNA clone libraries derived from the sludge incubated with (13)C-glucose and (13)C-propionate. To confirm that this bacterial group can utilize acetate, specific FISH probe targeting for Synergistes group 4 was newly designed and applied to the sludge incubated with (14)C-acetate for MAR-FISH. The MAR-FISH result showed that bacteria belonging to Synergistes group 4 significantly took up acetate and their active population size was comparable to that of Methanosaeta in this sludge. In addition, as bacteria belonging to Synergistes group 4 had high K(m) for acetate and maximum utilization rate, they are more competitive for acetate over Methanosaeta at high acetate concentrations (2.5-10  mM). To our knowledge, it is the first time to report the acetate-utilizing activity of uncultured bacteria belonging to Synergistes group 4 and its competitive significance to acetoclastic methanogen, Methanosaeta.
authors.affiliation: Department of Civil and Environmental Engineering, Graduate School of Engineering, Gunma University, Kiryu, Japan.
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Ito
authors.forename: Kazumi
authors.initials: K
authors.lastname: Yoshiguchi
authors.forename: Herto Dwi
authors.initials: HD
authors.lastname: Ariesyady
authors.forename: Satoshi
authors.initials: S
authors.lastname: Okabe
mesh_terms: D000085:Acetates / Q000378:metabolism*; D001105:Archaea / Q000145:classification* / Q000235:genetics / Q000378:metabolism*; D001345:Autoradiography; D001419:Bacteria / Q000145:classification* / Q000235:genetics / Q000378:metabolism*; D019605:Euryarchaeota / Q000235:genetics; D017404:In Situ Hybridization, Fluorescence; D008697:Methane / Q000378:metabolism; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D012722:Sewage / Q000382:microbiology*
chemical_list: D000085:Acetates; D012336:RNA, Ribosomal, 16S; D012722:Sewage; D008697:Methane