MICROBIAL COMPOSITION AND CHARACTERIZATION OF PREVALENT METHANOGENS AND ACETOGENS ISOLATED FROM SYNTROPHIC METHANOGENIC GRANULES

The microbial species composition of methanogenic granules developed on an acetate-propionate-butyrate mixture was characterized. The granules contained high numbers of adhesive methanogens (10(12)/g dry weight) and butyrate-, isobutyrate-, and propionate-degrading syntrophic acetogens (10(11)/g dry weight), but low numbers of hydrolytic-fermentative bacteria (10(9)/g dry weight). Prevalent methanogens in the granules included: Methanobacterium formicicum strain T1N and RF, Methanosarcina mazei strain T18, Methanospirillum hungatei strain BD, and a non-filamentous, bamboo-shaped rod species, Methanothrix/Methanosaeta-like strain M7. Prevalent syntrophic acetogens included: a butyrate-degrading Syntrophospora bryantii-like strain BH, a butyrate-isobutyrate degrading non-spore-forming rod, strain IB, a propionate-degrading spore-forming oval-shaped species, strain PT, and a propionate-degrading none-spore-forming sulfate-reducing rod species, strain PW, which was able to grow syntrophically with an H-2-Utilizing methanogen. Sulfate-reducing bacteria did not play a significant role in the metabolism of H-2, formate, acetate and butyrate but they were involved in propionate degradation.