Evaluation of thermophilic anaerobic microbial consortia using fluorescence in situ hybridization (FISH)

In this study we investigated the development of anaerobic biofilms in differential reactors and suspension cultures in batch reactors under thermophilic (55 degrees C) conditions. FISH, SEM, chemical and chromatographic analysis were used. The differential reactors reached 99.6%, 92.3% and 6.7% of acetic acid, COD and sulfate removal efficiencies, respectively, after 166 h of incubation time. The batch reactor reached 95.6% and 31.8% of acetic acid and sulfate removal efficiencies after 675 h, respectively. FISH results showed that bacterial cells rather than archaeal cells dominated biofilms. These cells, detected with the Bacteria specific probe (EUB338), accounted for 61.1% (+/-3.6) of the DAPI-stained cells and resembled acetate-oxidizing rods and Desulfotomaculum morphologies. Archaeal cells, which hybridized to the Archaea specific probe (ARC915), were also detected in biofilm but they accounted for 36.7% (+/-2.9) of the DAPI-stained cells. These cells were similar to Methanosaeta-like and hydrogenotrophic methanogen rods. In the suspension culture, archaeal cells (58.0%+/-3.8) morphologically similar to Methanosarcina and hydrogenotrophic methanogen rods were predominant over bacterial cells (41.0%+/-4.5), which resembled acetate-oxidizing rods and Desulfotomaculum morphologies. The percentage of sulfate-reducing bacteria cells (SRB) ranged from 12.2% (+/-2.5) to 21.7% (+/-2.8) in the biofilms and from 13.3% (+/-3.6) to 21.7% (+/-4.3) of the DAPI stained cells in suspension culture.