Poster Presentations

Session Title: Novel Technologies and Methods: Functional Community Analysis
Presentation Date: Thursday, August 21, 2008
Poster Board Number: 0263

LINKING STRUCTURE AND FUNCTION IN SYNTROPHIC BUTYRATE-DEGRADING CONSORTIA - INTEGRATING CULTIVATION AND RNA STABLE ISOTOPE PROBING

M. Altinbas¹, K. Roest², C.M. Plugge², I. Ozturk¹, A.J.M. Stams², H. Smidt^2
1Istanbul Technical University, Department of Environmental Engineering, Istanbul, Turkey, ²Wageningen University, Laboratory of Microbiology, Wageningen, Netherlands

Butyrate is an important intermediate of organic matter conversion under methanogenic conditions, accounting for up to 60% of methanogenesis in anaerobic bioreactors. The degradation of this intermediate depends on the syntrophic interaction of butyrate-oxidizing bacteria with hydrogen utilizing organisms. However, knowledge with respect to the degradation of butyrate is mostly limited to a few pure cultures, and the structure of butyrate degrading mixed cultures active in anaerobic bioreactors has not yet been characterized by culture-independent approaches. The objective of this study was therefore to elucidate structure-function relationships within syntrophic butyrate-oxidizing consortia, employing complementary culture-dependent and -independent techniques.
A combination of cultivation-based methods with a molecular biological approach was used to reveal the dominant syntrophic butyrate degraders in laboratory-scale UASB reactors. The application of MPN dilution enrichment techniques allowed estimating the numbers of different tropic groups in the reactor biomass, focusing on sulfate-reducers, acetogens and methanogens. Highest dilution cultures that yielded growth were examined to identify the dominant populations using cloning and sequencing of 16S rRNA gene fragments. In addition, active butyrate-degrading microorganisms were identified by using a combined approach of RNA-based DGGE fingerprinting of RT-PCR-amplified 16S rRNA fragments, cloning and sequencing together with RNA-Stable Isotope Probing (SIP) with ¹³C-labeled butyrate and propionate. These analyses indicated that populations most closely related to Syntrophomonas spp. were the dominant, but not the only butyrate-degrading bacteria active in the reactor. In conclusion, this study provided novel leads for the identity of syntrophic butyrate-oxidizing bacteria, and their isolation and further physiological and genomic characterization.