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The microbial communities in 6 granular sludge samples taken from a lab-scale EGSB reactor operated under different organic loading rates (OLR) at 20 degrees C were studied using PCR-DGGE and RTQ-PCR technique. The results indicate that as the OLR increased from 1.5 kg/(m3 x d) to 10.0 kg/(m3 x d), the microbial communities of archaea and eubacteria in the 6 sludge samples are not changed greatly. The archaea population is highly similar among the 6 samples. The Shannon indexes of archaea population are 5.51, 5.88, 5.47, 5.25, 5.32 and 5.11, respectively. Except the seed sludge, the eubacteria population is similar among the other 5 samples. The Shannon indexes of eubacteria population are 2.97, 5.07, 5.44, 6.38, 6.66 and 5.21, respectively. The dominant archaea in the 6 granular samples are Methanobacterium, Methanocorpusculum, Methanosaeta and Methanospirillum. As the OLR of the reactor increased and the operation time elapsed, Methanocorpusculum parvum and Methanospirillum hungatei, both are hydrotrophic methanogens, become the dominant archaea. The archaea content in the samples decreases slightly at the beginning, but increases later and finally reaches to a level obviously higher than that in the seed sludge.

An anaerobic, mesophilic, syntrophic benzoate-degrading bacterium, designated strain FB(T), was isolated from methanogenic sludge which had been used to treat wastewater from the manufacture of terephthalic acid. Cells were non-motile gram-positive rods that formed spores. The optimum temperature for growth was 35-40 degrees C, and the optimum pH was 7.0-7.2. A co-culture with the hydrogenotrophic methanogen Methanospirillum hungatei converted benzoate to acetate, carbon dioxide, and methane. Butyrate transiently accumulated at a high concentration of 2.5 mM during degradation. Besides benzoate, no other compound tested supported growth of the co-culture. Crotonate supported growth of strain FB(T) in pure culture. Furthermore, the strain degraded benzoate in pure culture with crotonate as co-substrate to produce acetate and butyrate. The strain was not able to utilize sulfate, sulfite, thiosulfate, nitrate, fumarate, or Fe(III) as electron acceptor. The G+C content of the DNA was 46.8 mol%. Strain FB(T) contained MK-7 as the major quinone and C(16:1) as the major fatty acid. 16S rDNA sequence analysis revealed that the strain was a member of the genus Sporotomaculum, even though it exhibited significant differences, such as the capacity for syntrophic growth, to the known member of the genus. Hence, we propose the name Sporotomaculum syntrophicum sp. nov. for strain FB(T). The type strain is strain FB(T) (DSM 14795, JCM 11475).

The pathway of propionate conversion in a syntrophic coculture of Smithella propionica and Methanospirillum hungatei JF1 was investigated by (13)C-NMR spectroscopy. Cocultures produced acetate and butyrate from propionate. [3-(13)C]propionate was converted to [2-(13)C]acetate, with no [1-(13)C]acetate formed. Butyrate from [3-(13)C]propionate was labeled at the C2 and C4 positions in a ratio of about 1:1.5. Double-labeled propionate (2,3-(13)C) yielded not only double-labeled acetate but also single-labeled acetate at the C1 or C2 position. Most butyrate formed from [2,3-(13)C]propionate was also double labeled in either the C1 and C2 atoms or the C3 and C4 atoms in a ratio of about 1:1.5. Smaller amounts of single-labeled butyrate and other combinations were also produced. 1-(13)C-labeled propionate yielded both [1-(13)C]acetate and [2-(13)C]acetate. When (13)C-labeled bicarbonate was present, label was not incorporated into acetate, propionate, or butyrate. In each of the incubations described above, (13)C was never recovered in bicarbonate or methane. These results indicate that S. propionica does not degrade propionate via the methyl-malonyl-coenzyme A (CoA) pathway or any other of the known pathways, such as the acryloyl-CoA pathway or the reductive carboxylation pathway. Our results strongly suggest that propionate is dismutated to acetate and butyrate via a six-carbon intermediate.