A SYNTROPHIC PROPIONATE-OXIDIZING, SULFATE-REDUCING BACTERIUM FROM A FLUIDIZED-BED REACTOR

A mixed-culture HP1 was enriched with propionate/sulfate from a methan ogenic fluidized bed reactor fed with propionate as the sole organic c arbon source in a medium low in sulfate. The mixed-culture contained s train HP1.1 as the only propionate-oxidizer, which was Gram-negative, lemon- or peanut-shaped, 0.95-1.15 x 1.4-2.4 mu m in size, occurred si ngly or in pairs, and did not form endospores. Strain HP1.1 oxidized p ropionate to acetate and carbon dioxide with concomitant reduction of sulfate. Scanning electron microscopy revealed that strain HP1.1 was m orphologically distinct from Syntrophobacter wolinii and Desulfobulbus propionicus. We separated strain HP1.1 from other strains by Percoll gradient centrifugation, and from these cells the total sequence of 16 S rDNA from the PCR-amplified 16S rRNA-gene from DNA was obtained. The phylogenetic analysis revealed that strain HP1.1 was less closely rel ated to Syntrophobacter wolinii than to two recently described, propio nate-oxidizing strains MPOB and KoProp1 within the 6-subclass of the P roteobacteria (Dorner, 1992; Harmsen et al., 1995), while a more dista nt relationship was found to Desulfobulbus propionicus.