Abstract
DNA-based stable-isotope probing was applied to identify the active microorganisms involved in syntrophic butyrate oxidation in paddy field soil. After 14 and 21 days of incubation with [U-(13)C]butyrate, the bacterial Syntrophomonadaceae and the archaeal Methanosarcinaceae and Methanocellales incorporated substantial amounts of (13)C label into their nucleic acids. Unexpectedly, members of the Planctomycetes and Chloroflexi were also labeled with (13)C by yet-unclear mechanisms.