Acetic acid and hydrogen metabolism during coculture of an acetic acid producing bacterium with methanogenic bacteria

Two microorganisms originally existing as a mixed culture obtained from an anaerobic digester fluid were separated for pure and coculture studies. One of these was motile, Gram-negative, and non-sporeforming, and it required yeast extract for growth and acetic acid production. This isolate produced H2 and did not need H2 and (or) CO2 for growth and acetate formation. The other isolate was a methanogen which resembled Methanobacterium arbophilicum in morphology and substrate specificity. Coculture growth of the two isolates in yeast extract broth (80% N2–20% CO2 gas phase) indicated that the non-methanogen produced up to four to five times more H2 than when grown separately. Although the growth of the non-methanogen was not enhanced by the removal of H2 by the methanogen, the hydrogen produced was essential for the growth of methanogen. Similar results were obtained when the non-methanogen was cocultured with Methanospirillum hungatii GP1. Cultivation of the non-methanogen in the presence of M. hungatii GP1 (under abundance of 80% H2–20% CO2) indicated that the acetate produced was consumed by M. hungatii, without inhibiting the growth of the other culture.