Acetogenesis is one of the main reactions of this stage, in this, the intermediary metabolites produced are metabolized to acetate, hydrogen and carbonic gas by the three main groups of bacteria:
Winter y Wolfe, in 1979, demonstrated that A. woodii in syntrophic association with Methanosarcina produce methane and carbon dioxide from fructose, instead of three molecules of acetate.[6]Moorella thermoacetica and Clostridium formiaceticum are able to reduce the carbonic gas to acetate, but they do not have hydrogenases which inhabilite the hydrogen use, so they can produce three molecules of acetate from fructose. Acetic acid is equally a co-metabolite of the organic substrates fermentation (sugars, glycerol, lactic acid, etc.) by diverse groups of microorganisms which produce different acids:
^Marchaim, U. (1992). FAO Agricultural Services Bulletin – 95: Biogas process for sustainable development, FAO – Food and Agriculture Organization of the United Nations, ISSN 1010-1365 (1/9/2003).
^Alexiou, I.E. and Panter, K. (2004). A review of two phase applications to define best practice for the treatment of various waste streams. Anaerobic Digestion 10th World Congress, September 2004. Montreal, Quebec, Canada.
^(in Spanish) Cairó, J.J. and París, J.M. (1988). Microbiología de la
digestión anaerobia, metanogénesis. 4o Seminario de Depuración Anaerobia de Aguas Residuales. Valladolid. F.F. Polanco, P.A. García y S. Hernándo. (Eds.) pp. 41–51.
^Dinopolou, G., Rudd, T. and Lester, J.N. (1987). Anaerobic acidogenesis of a complex wastewater: I. The influence of operational parameters on reactor performance. Biotech. And Bioeng. 31: 958 – 968.
^(in French) Laroche, M. (1983). Metabolisme intermediaire des acides gras volatils en fermentation methanique. These de Docteur – Ingenieur en Sciences Alimentaires_Fermentations. Institut National de la Recherche Agronomique, France.
^Winter, J.U. and Wolfe, R.S. (1979). Complete degradation of carbohydrates to CO2 and methane by syntrophic cultures of Acetobacterium woodii y Methanosarcina barkeri. Arch. Microbiol. 121: 97 – 102.